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1 Unit I
1
INTRODUCTION TO JAVA
PROGRAMMING
Unit Structure
1.0 Objectives
1.1 Introduction
1.2 History
1.3 Java Architecture and its components
1.3.1 The Java Virtual Machine
1.3.1.1 JVM Components
1.3.2 Java Runtime Environment
1.3.3 Java Development Kit
1.4 The Java API
1.5 Java Platform
1.6 Lambda Expressions
1.7 Methods References
1.8 Type Annotations
1.9 Method Parameter Reflection
1.10 Setting the path environment variable
1.11 Java Compiler and Interpreter
1.12 Java class file
1.13 Java Programs
1.14 Java Applications
1.15 Whitespace and case sensitivity
1.16 Identifiers and keywords
1.17 Comments
1.18 Braces and code block
1.19 Variables and variable name
1.20 Summary
1.21 List of References
1.22 Bibliography
1.23 Model Questions
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2 1.0 OBJECTIVES
In this chapter, you will be going to learn following topics:
Introduction to java programming and its various features
Java architecture
JVM Components
Different Java platforms
How to write and execute a java program?
Different terms used in java language like variables, keywords,
identifiers
1.1 INTRODUCTION
What is Java?
Java is a programming language and platform. Java is High -level,
object -oriented programming language developed by sun microsystems. It
is simple programming language. Java Language is used to developed
Standalone Applications, Web Applications, Enterprise Applications and
Mobile Applications. Java Provides a runtime En vironment (JRE) and
Java API, that’s why it is called as a platform.
Features of Java language:
1) Simple: Java was designed to be a very easy to learn and understand
and use effectively. If you understand the basic concepts of object -
oriented programming, learning java will be easier.
2) Object - Oriented: Java is purely an object -oriented programming
language. In Java, everything is an object which has some data and its
own behavior.
Following are some basic concepts of OOPs:
Class: Class is col lection of objects. You can create multiple objects
of a class. It represents properties and methods that are common to all
objects of one type.
Object: Any entity that has state and behaviors is called as an object.
Object can be defined as instance of a class.
Inheritance: Inheritance is a mechanism in java which allows one
class to inherit properties and behavior of another class (parent class).
Polymorphism: If one task is performed in many different ways, it is
called as polymorphism. In java method o verloading and method
overriding is used to implement polymorphism.
Abstraction: Hiding internal details and showing only functionality
is known as abstraction. For example, we don’t know the internal
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3 Encapsulation: B inding or wrapping code and data together into a
single unit are known as encapsulation. For example, capsule
wrapped it with so many medicines.
3) Robust: Java is robust because it provides strong memory management
and automatic garbage collection. Java Virt ual machine is responsible
to manage allocation and deal location of memory for objects. It will
automatically free the memory for such objects which have not been
used in java application. It also provides compile time and run -time
error checking mechanis m.
4) Platform Independent: Java code is not complied into platform
specific machines. Java Code can be executed on multiple platforms
like Windows, Linux, Mac/OS etc.
5) Secured: We can develop secured and virus free applications. Java is
secured because java programs always get executed inside java virtual
machine which has no interaction with OS.
6) Architecture -Neutral: Java has no implementation dependent features.
In java size of the primitive data type is fixed. Once byte code is
generated it can be execut ed on 32 -bit architecture as well as 64 -bit
architecture.
7) Portable: Java is writing once and run anywhere language. Java byte
code generated after compilation can be executed on any machine.
8) High - Performance: Java is an interpreted language. It faster tha n other
traditional interpreted languages.
9) Distributed: Java is distributed because it supports creating distributed
applications. Using RMI and EJB you can create distributed
applications in java.
10) Multi -Threaded: Java multi -threading allows you to creat e multiple
threads to executed simultaneously. With this feature we can divide
program in multiple threads that will execute different tasks at once.
11) Dynamic: Java support dynamic loading of classes.
1.2 HISTORY
Java language was Initially developed by James Gosling, Patrick,
Chris Wart hand Mike Sheridan at Sun Microsystems in 1991.This
language was initially called “Oak” but was renamed “Java” in 1995.
Initially it was developed to create software to be embedde d in various
electronic devices like microwave ovens, remote controls, set -top boxes
etc. munotes.in
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4 Sun micro system releases first version JDK 1.0 in Jan 1996. It
provides Write once and run anywhere functionality. After first release
they have added various new f eatures in each new release version. Second
version JDK 1.1 was released in Feb 1997.
On 13 November 2006 Sun Micro system released some part of
Java Virtual Machine(JVM) as free and open source software, under the
General Public License. On May 8, 2007 , Sun finished the process of
making all of its JVM Code available under free and open source
distribution term, except small portion of the code to which sun did not
have copyright. In 2010 java was acquired by Oracle Corporation. Later
on, Oracle Corpora tion keeps on releasing new versions by adding many
new features in each version. Oracle released current version JDK SE 16
on 16 march, 2021.
1.3 JAVA ARCHITECTURE AND ITS COMPONENTS
Java Architecture includes components JVM, JRE and JDK. It
combines the pr ocess of compilation and Interpretation. It defines all the
processes involves in creating a java program. Architecture explains all
steps like creating program, how program is compiled and how it is
executed.
Java architecture performs following steps:
1) In Java, Program execution is a two -step process which include
Compilation and Interpretation.
2) In first Step, Java compiler converts the source code into byte code.
3) In second step, JVM converts byte code into machine code.
4) Then machine code is executed by O perating System.
Fig. Java Architecture
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5 Components of Java Architecture
Java Architecture includes three main components:
1) Java Virtual Machine (JVM)
2) Java Runtime Environment (JRE)
3) Java Development Kit (JDK)
1.3.1 The Java Virtual Machine
Java virtual machine is a part of Java Runtime Environment. The
primary function of JVM is to execute the java bytecode. It is a
specification that provides java runtime environment in which java
bytecode is executed. JVM is respon sible to load java code in memory and
calls main method present in java code and then execute that method.
Java language provides a feature of Write Once Run Anywhere.
Which means we can write code once and execute it anywhere and on any
operating system. Java program executes on any platform only because of
Java Virtual Machine.
1.3.1.1 JavaVirtual Machine Components
JVM performs following operations:
Loads java byte code, verifies code, execute code, provides
runtime Environment
Fig. JVM Architecture
1) Class Loader: Class Loader is used to loads the .class files into
memory. Whenever we execute the java program, class loader loads it
first.
There are three built in class loader are available in Java.
1) Bootstrap Class Loader: Bootstrap class loader is super class of
Extension Class Loader. It loads all the packages included in Java
Standard Edition like java.lang package, java.io package, java.util
package, java.net package and so on.
2) Extension Cla ss Loader: Extension classloader is subclass of
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6 loads all jar files present in the $JAVA_HOME/jre/lib/ext
directory.
3) Application Class Loader: Application Classloader is subclass of
the Extension Classloader. It loads files from classpath. By default,
classpath is set to a current working directory. You can able to
modify classpathby using -cp or -classpath command.
2) Method Area: Method Area stores the all the class level data such as
runtime constant pool, fields, method data and code for methods. There
is only one method area par JVM.
3) Heap: Heap memory created when JVM Start up. It stores all the
objects created during program execution and their corresponding
instance variable. It is the run -time data area from which memory for
all class instances and array is allocated. There is only one heap area
par JVM.
4) Stack: Java Stack memory stores Stack frames, local variable, method
calls, partial results. Whenever a new thread is created in the JVM, a
separate JVM stack is also created at the same time for that thread. A
new frame is created whenever a method is invoked and it is deleted
when method invocation process is completed.
5) Program Counter (PC) Registers: Program Counter Register stores
address of the currently executing JVM Instruction. JVM Support
Multiple threads, so each thread has it own PC register. Once the
instruction is executed PC register is updated with new instru ction.
6) Native Method Stack: It contains all the native methods used in
application. These methods are written any other language than java
like c, c++ etc. For each thread separate native Method Stack is created.
7) Execution Engine: Once the bytecode has b een loaded into memory,
next step is to execute the program. Execution engine is responsible to
execute the program. Before executing program, bytecode need to be
converted into machine language instructions. The JVM uses
interpreter or JIT Compiler to co nverts byte code into machine
language instructions.
8) Execution engine includes:
Interpreter: The interpreter read and executes byte code instructions
line by line.
Just-In-Time Compiler: it is used to improved performance. JIT
complies the parts of the bytecode that have similar functionality at the
same time. It reduces amount of time needed for compilation.
Garbage Collector: The Garbage Collector collects and remove
unused objects from th e heap area. It is the process of automatically munotes.in
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7 destroying unused objects and making runtime memory available to use
for some other objects.
9) Java Native Interface: Java Native Interface(JNI) provides an
interface to communicate with another application wr itten in another
language like c, c++ etc. Java provides execution of native code
through JNI.
10) Native Libraries: Java Native Libraries provides a collection of
libraries which are written in other programming languages needed by
execution engine.
1.3.2 Java Ru ntime Environment (JRE)
Java Runtime Environment is a set of software tools which are
used for developing Java applications. It is used to provide a runtime
environment where we can execute our java program. JRE is part of JDK
means it get install automati cally along with JDK. JRE includes JVM, set
of libraries, plugins and applet support. JRE initiates JVM for its
execution.
1.3.3 Java Development Kit (JDK)
We need JDK for execution of java programs and for developing
java applications. Java Development Kit is a software development
environment which is used to developed Java applications. It includes
JRE, a compiler, an interpreter, aa debugger and other tools like document
generator etc.
1.4 THE JAVA API
Java API (Application Programming Interface) provides a large
collection of packages. Each package includes a large collection of classes
and interfaces along with their methods.
Java API Packages:
java.io Provides Classes for system input and output through data
streams and the file system.
java.net Provides classes for implementing networking application.
java.util It contains date and time facilities and collection
framework and classes.
java.awt Provides a large list of classes for creating user interfaces
and for painting graphics and images.
java.sql Provides classes and interface required for accessing and
processing data stored in data based
javax.swing Provides a set of lightweight components required for
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8 Java.math Provides classes and interfaces for performing arbitrary -
precision integer arithmetic and arbitrary -precision decimal
arithmetic..
1.5 JAVA PLATFORM
Java platforms is a collection of programs that helps programmer
to develop and run java programs written in java programming language.
It is hardware and software environment in which programs runs. Java
platform includes an JVM, a compiler and set of libraries called as API.
Java Platforms:
1) Java SE (Standa rd Edition): It is a java programming platform.
It includes java programming APIs like java.io, java.net,
java.util,java.math, etc.
2) Java EE (Enterprise Edition): It is an enterprise platform which
is usedto developed web applications and enterprise applications.it
includes java technologies like Servlet, JSP, Web Services, EJB
etc.
3) Java ME (Micro Edition): Java micro edition used to develop
mobile applications.
1.6 LAMBDA EXPRESSIONS
Lambda Expression is an anonymous method (unnamed method).
Lambda expression is used to implement a method defined by functional
interface. Lambda expression is treated as function.
Lambda expression provides an implementation of fun ctional
interface. Functional interface is an interface which has only one abstract
method. A method which includes only declaration not any
implementation is called as abstract method. Functional interface is also
known as Single Abstract Method (SAM) int erface.
Syntax for creating functional interface:
interface interface_name
{
Return_typemethod_name(); //abstract method
}
Example:
1) interface Draw
{
void circle();
} munotes.in
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9 2) interface Addition
{
add(int a, int b);
}
Lambda Expression Syntax:
(argument list) ->{ body }
-> This operator is called as lambda operator or arrow operator. This
operator divides lambda expression in two parts, left side includes
parameters required by lambda expression and right side include body,
which specifies actions of the lambda expression. Body part includes
expressions or statements for lambda expression.
Examples:1) () -> 123.14
This lambda expression returns constant value 123.14.
2) () -> 12*6
Program:
interface Area
{
void findArea();
}
public class LambdaEx pressionDemo1
{
public static void main(String arg[])
{
Area obj1;
int r = 3;
//Lambda Expression without any argument
obj1 = () ->System.out.println("Circle Area:" + (3.14*r*r));
obj1.findArea();
int side = 5;
obj1 = () ->System.out.prin tln("Square Area: " +( side*side));
obj1.findArea();
}
}
Output:
Circle Area:28.259999999999998
Square Area: 25
Lambda expression with parameter:
1) (n) -> n*n
2) (r) -> 3.14*r*r
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10 Program:
interface Calculate
{
int display(int p, int q);
}
public class LambdaExpressionDemo2
{
public static void main(String arg[])
{
Calculate obj1;
obj1 = (a,b) -> (a+b); //lambda expression with argument
System.out.println("Addition: " + obj1.display(10,20));
obj1 = (h,w) -> (h*w);
System.ou t.print("Rectangle Area:" + obj1.display(5,4));
}
}
Output:
Addition: 30
Rectangle Area:20
1.7 METHOD REFERENCES
Lambda Expression is used to create anonymous methods. Method
references is similar to lambda expression. Sometimes, a lambda
expression only calls an existing method. When you want to refer existing
method by name then you can use method references. Method reference
provides a way to refer to a method without executing. Whenever you are
using a lambda expression just to refer a method, you can replace that
lambda expression with method reference.
Types of method references:
1) Method reference to a static method:
You can refer a static method created in class.
To create static method reference use following syntax:
Class_name :: m ethodName
Program:
interface Calculate //functional interface
{
void cube(int a); //abstract method munotes.in
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11 }
class StaticReference
{
public static void display(int b)
{
System.out.println("Cube: " + (b*b*b));
}
public static void main(String arg[])
{
Calculate c = StaticReference :: display;
c.cube(5);
}
}
Output:
Cube: 125
2) Method Reference to anInstance Method
To create instance method reference use following syntax:
Object_reference :: methodName
This syntax is similar to static method r eference, except it uses a
object reference instead of class name.
Program:
interface Calculate
{
void square(int a);
}
class InstanceReference
{
public void display(int b)
{
System.out.println("Square: " + (b*b));
}
public static void main(String arg[])
{
InstanceReference instance =new InstanceReference();
Calculate c = instance :: display;
c.square(15);
}
}
Output:
Square: 225
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12 3) Method Reference to a constructor
Constructor: Constructor is a one kind of function in java which has
same name as the class name. It does not have any return type.
Constructor will get called automatically after creating an object (instance)
of a class. Constructor is mostly used to initialized object of class. Every
time you will create object of a class, th e constructor will get executed.
Syntax: class_name() {}
Example of creating constructor:
Class Demo
{
Demo() //constructor
{
//Statements
}
}
Similarly, you are creating references to a method, you can also
create a reference to a constructor.
Syntax for creating reference to a constructor:
Class_name :: new
Program:
interface Calculate
{
void display();
}
public class MyConstructor
{
MyConstructor()
{
System.out.println("Creating reference to a constructor");
}
public static void main(String arg[])
{
Calculate c = MyConstructor :: new;
c.display();
}
}
Output:
Creating reference to a constructor
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13 1.8 TYPE ANNOTATIONS
Java Annotations are used to provide supplementary information
about your program. Java Annotat ions represents a metadate or
information attached with class, interface, methods, instance variables and
constructor etc. Annotations can be used by compiler to detect errors or
suppress warnings. Annotations can be applied while declaring methods,
fields , classes, constructor and other program elements.
All the annotations in java start with ‘@’ symbol. Annotations do
not change action or execution of a compiled program. Annotations are
not considered as comments as they change the way the compiler treat s a
program.
Types of Java Annotations:
1) Marker Annotation: The purpose of market annotation is to mark a
declaration . Marker annotation do not contain any members or do not
consist of any data. Marker interface in java does not consists of any
method, for declaring this interface we can use marker annotation.
@Override and @Deprecated are the examples of Marker Annotati on
Example of declaring marker Annotation:
@TestAnnotation()
@interface MyAnnotation{}
2) Single Value Annotation:
Single Value Annotation contain only one value. They allow
shorthand form of specifying the value to of the member. While using this
annotat ion, we only need to specify the value for that member and also do
not need to specify the name of the member.
Example:
@TestAnotation(name = “amit”)
@MyAnnotation(value= 10)
3) Multi Value Annotation:
Multi value Annotation consists of multiple data memb ers, values and
pairs.
Example of declaring Multi value annotation:
1) @interfaceMyAnnotation
{
int id();
String name();
String class();
}
2) // you can also provide default value to each member
@interface MyAnnotation2
{
int id() default 101; munotes.in
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14 String name() “Pranali”;
}
3) @TestAnnotaion(id = 1, name= “shruti”, class = “SYIT”)
4) @Author(name= “balguru swami” , date = “28/8/2021”)
Predefined Java Annotations used in java code:
1) @Deprecated: The @Deprecated Annotation is marker annotation
that indicat es the element is deprecated and should no longer be
used. The compiler generated a warning whenever program uses a
method, class and field with @Deprecated annotation.
2) @Override: the @override annotation informs the compiler that
element is meant to override an element declared in a superclass.
3) @SuppressWarnings: The @SuppressWarnings annotation
instruct the compiler to suppress warning that are generated while
program executes. The java langua ge specification lists two
categories of warnings: Deprecation and Unchecked.
Example: To suppress particular category of warning, we use
@SupressWarning(“Deprecation”)
To suppress multiple category of warnings, we use
@SupressWarning({“Deprecation”, “ Unchecked”})
4) @Safevarargs: This annotation asserts that the annotated method
or constructor does not perform unsafe operations on its varargs
(variable number of argument).
5) @Functional Interface: This annotation is introduced in JDK SE
8, indicates that the type declaration is intended to be a functional
interface.
Predefined Java annotation applied to other Annotation:
1) @Retention: Retention annotation specifies how the marked
annotation is stored:
@RetentionPolicy.SOURCE : The marked annotation is
retained only in the source level and is ignored by the
compiler.
@RetentionPolicy.CLASS : The marked annotation is
retained by the compiler at compile time, but it is ignored
by JVM.
@RetentionPolicy.RUNTIME : The marked annotation is
retained by the JVM so that it can be used by the runtime
environment.
2) @Documented: Documented annotation indicated that whenever
the specified annotation is used those elements should be
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15 3) @Terget: Target annotation marks another annotation to restrict
what kind of java elements the annotation can be applied to. It
specifies one of the following element types as its value:
@ElementType.ANNOTATION_TYPE
@ElementType.CONSTRUCTOR
@ElementType.FIELD
@ElementType.LOCAL_VARIABLE
@ElementType.METHOD
@ElementType.PACKAGE
@ElementType.PARAMETER
@ElementType.TYPE
4) @Inherited: This annotation indicates that the annotation type can
be inherited from the super class
5) @Repeatable: repeatable annotation indicates that the marked
annotation can be applied more than once to the same declaration
or type use.
1.9 METHOD PARAMETER REFLECTION
Method contains executable code which may be invoked, once you
called method. By default, .class file generated after compilation does not
store formal parameter names of any method or constructor. Method
Parameter Reflection provides you feature in which you can able to store
names of formal parameters. The java.lang.reflect package provides you
all classes required for method parameter reflection. Method and
Parameter class are main ly used to store and read formal parameter.
Method class:
The java.lang.reflect.Method class provides APIs to access
information about a method’s modifiers, return type, parameter,
annotations and thrown exception. It is also used to invoked methods.
Reflected method can be a class method or instance method.
Method Class Methods
Method Description
int getModifiers() Returns java language modifiers for the
executable represented by objects.
String getName() Return the name of the method
represented by this method object.
Annotation[][]
getParameterAnnotations() It returns array of array of annotations
that represents the annotations of the
formal parameter, in declaration order,
of the executable represented by object.
ClassgetReturnType() It returns a class object that represents
the formal return type of the method
represented by this Method Object munotes.in
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16 int getParameterCount() Returns a number of formal parameters
for the executable represented by this
object.
Class[]
getParameterTypes() Returns an array of Class objects that
represents the formal parameter types, in
declaration order, of the executable
represented by object.
Parameter Class:
It is used to obtain information about method parameters, including
its name, and modifier. To store formal parameter names in a particular
.class file, and thus enable the reflection API to retrieve formal parameter
names, compile the source file with the -parameters option to the javac
compiler.
Parameter Class Methods:
Method Description
int getModifiers() Get the modifier flags for the parameter
represented by this parameter object.
String getName() Return the name of the parameter.
Type
getParameterizedType() Return a type object that identifies the
parameterized type for the parameter
represented by this parameter object.
ClassgetType() Return a class object that identifies the
declared type for the parameter represented
by this parameter object.
booleanisNamePresent() Return true if the parameter has a name
according to class file.
booleanisImplicit() Return true if this parameter is implicitly
declared in source code.
booleanisSynthetic() Return true is this parameter is neither
implicitly nor explicitly declared in source
code.
Program:
Calculate.java
public class Calculate
{
int add(int a, int b, int c)
{
return (a+b+c);
}
int sub(int a, int b)
{ munotes.in
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17 return (a -b);
}
}
Compile this class with following command:
javac -parameters Calculate.java
MethodReflection.java
import java.lang.reflect.*;
public class MethodReflection
{
public static void main(String arg[])
{
Calculate c = new Calculate();
Class obj1 = c.getClass(); //creating instance of Class
// returns array of methods from calculate class
Method[] m1 = obj1.getDeclaredMethods();
for(Method m2 :m1)
{
System.out.print(m2.getName()); //returns name of method
Parameter p[] = m2.getParameters(); // returns parameter
od each method
for(Parameter p2: p)
{
System.out.print(" " + p2.getParameterizedType());
System.ou t.print(" " +p2.getName());
}
System.out.println();
System.out.println(" no of parameter : " +
m2.getParameterCount());
System.out.println(" Return Type : " +
m2.getReturnType());
}
}
}
Command to compile and execute the program
Compile: javac MethodReflection.java
Execute: java MethodReflection
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18 1.10 SETTING THE PATH ENVIRONMENT VARIABLE
The Path is the system variable that your operating system uses to
locate needed executables from the command line. If you have saved your
java file in JDK/bin directory, the path is not required to be set. If you
save your java files in other directory then you need to set path of JDK.
There are two ways to set the JDK path:
1) Temporary: It will be valid till your command prompt is open.
Steps to s et temporary path of JDK:
Open the command prompt.
Copy the path of JDK/bin Directory
Write the command in command prompt: set path = copied_path
Example: Set path=” C: \Program Files \Java \jdk1.8.0_261 \bin”
2) Permanent:
Steps to set Permanent path of JDK in Windows 10 and Windows 8:
1) Open My Computer properties.
2) Click on Advanced System Setting
3) Click on Environment Variable options.
4) In system variable section, click on new option.
5) Specify variable name as Path and in place of variable value specify
path of java bin folder, then click OK.
1.11 JAVA COMPILER AND INTERPRETER
Java program execution is a two -step process i.e., Compilation and
interpretation.
Java Compiler: Compiler Translate the source code written by
programmer into byte code. The bytecode generated after compilationis
save with .class file extension. File name is same as a class name.
Compiler also responsible to check source code for errors. It cannot f ix
errors if present in program; it generates error message and programmer
have to solve that all errors. If your program is having no errors then
compiler convert it into byte code.
Java Interpreter:
Java Interpreter is a computer program, which impleme nts the
JVM specification and helps to actually execute the java bytecode. After
compilation compiler generates bytecode (.class file), interpreter takes this munotes.in
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19 byte code and translate it into machine code. Then interpreter executes
instruction available in machine code line by line.
1.12 JAVA CLASS FILE
Java class file contains bytecode. It is saved with .class extension.
This file automatically gets generated after successful compilation of the
program. It has a same name as the class name. This file is execu ted on
Java Virtual Machine. If your java program contains more than one class,
then in such cases after compilation we get same number of .class files as
the number of classes present in java program. It is saved in same
directory where your java file is stored.
1.13 JAVA PROGRAMS
Structure of java program:
Java source code file saved with .java extension. Source code
includes one class definition. We can also include multiple classes t single
source code file. Class includes one or more methods. All the me thods
need to be defined inside the class. Within the curly braces of the method,
you can write instructions that method should be performed. Method
includes collection of statements. Every Java program must have at least
one class and one main method in e ach program.
class Example
{
public static void main(String arg[])
{
System.out.print("we are learning java programming");
}
}
Program should be saved with Example.java file name.
Parameters use in above java program:
class: class is inbuild keyword use to declare class in java. Class keyword
followed with class_name.
public: It is a access specifier which represents the visibility of main
method. Public means accessible everywhere.
static: It is defined keyword in java. If you declared any method as a static
in java, then this method should be called without creating any object of
the class. Main method is executed by JVM, so there is no need to create
any class object to called main method.
void: It is one return type. Void means not returning any value.
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20 main(): main is starting point of program execution. Java program
execution starts from main method.
String arg[]: It is argument to the method. Main method must be array of
string. This will be use to read command line argument.
System.out.print(): It is used to print statement on output screen. System
is a class, out is an object. Print method is used to print statement.
Java program will be executed on command prompt.
Command used to compile java program:
C:\>javac classname.java
example: javacExample.java
This javac compiler create a file with name Example.class stored
in save location where you have saved java file. It is the byte code version
of original program. This byte code is latter on executed by Java Virtual
Machine.
command use to execute the java program:
c:\>java classname
example: java Example
when you run this program, following output is displayed.
Output:
we are learning java programming
1.14 JAVA APPLICATIONS
There ar e four different types of applications we can developed using
java language.
1) Standalone Application: Standalone Application also called as
desktop application or windows -based application. This kind of
software we need to install on every system where you w ant to use
that software. Examples of standalone applications are office suite,
media player and all other programming software like turbo++
compiler, python etc. AWT and SWING in java used to developed
standalone applications.
2) Web Application: Like standalone applications which need to be
install on machine, Web Applications we can be access through
internet. It is installed on the server and users can used it through
internet. Currently, Servlet, JSP, Struts Framework, Spring
Framework, Hibern ate Framework etc.
3) Enterprise Application: An Application that is distributed in
nature are called as enterprise application. Examples of enterprise
applications are banking application, Skype, call center and
customer support application, Health Informat ion Management
system etc. Technologies used to develop Enterprise Application munotes.in
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21 include Java Persistence API, Java Transaction API, Java
Enterprise Bean, Java Mail etc.
4) Mobile Application: An Applications which is created for mobile
devices are called as Mo bile Application. It will work only on
smart phones.
1.15 WHITESPACE AND CASE SENSITIVITY
Whitespace: Java is free form language. There is no need to follow any
special indentation while writing program like you are doing in python
programming language. This means you can write entire java program in
one line. Whitespace in java includes a space, tab and new line.
Case Sensitivity: Java is case sensitive language. In java program add
variable will be different from ADD variable. If you are using some
inbuild methods in program then it needs to use in same defined format.
Example: int add;
int ADD;
Both will be considered as completely different variables.
1.16 IDENTIFIERS AND KEYWORDS
Identifiers: Identifier is a sequence of one or more characters. Identifiers
are used to name things, like variables, methods and classes. An Identifier
is descriptive sequence of uppercase and lowercase letters, numbers, and
underscore sign and dollar -sign.
Rules for defining Identifiers:
You can use combination uppercase and lower -case letters, numbers,
dollar -sign and underscore sign for creating variable name. No other
special characters are allowed to use while creating identifiers.
Identifier name must not be sta rt with digit. Example “111add” will
not be consider as valid identifier.
Identifiers are case sensitive.
Identifier name should be start with either alphabet, underscore sign or
dollar -sign.
Inbuild keywords in java cannot be used as an identifiers.
Exam ple: varaible1, $add, _test2;
This allare the valid identifiers in java language.
Example: 1test, lower -case, ok/cancel;
This all are invalid identifiers in java. Wecannot able to use dash
or any other special character while creating identifiers. munotes.in
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22 Keywords: Keywords are the reserved words in java. Keywords cannot be
used as identifiers, means you cannot use it as variable name, method
name and class name. The keywords const and goto are reserved but
currently not in use. The keyword strictfp is adde d in JDK 1.2 version.
The keyword assert is added in JDK 1.4 version. Enum keyword is added
in JDK 5.0.
abstract continue for new switch
assert default goto package synchronized
boolean do if private this
break double implements protected throw
byte else import public throws
case enum instanceof return transient
catch extends int short try
char final interface static void
class finally long strictfp volatile
const float native super while
Java reserved other four names like null, true, false and var. you may not
use these words as variable, class and method name.
Example: class Example2
{
public static void main(String arg[])
{
int x=10;
int y=20;
int z= x+y;
System.out.print("Addition:" + z);
}
}
Output:
Addition: 30
In this example, Example2, arg, x,y and z are called as identifiers
which are user defined.
Class, public, static, void, main, String is called as keywords which
are predefined in java.
1.17 COMMENTS
Comments are statements in java which are not executed by java
compiler and interpreter. Comments are used to make the program more
readable by adding details of the code. You can add small description
about your program in comments section. You can use comments to
provide description about variab le, methods, class and any other
statement. munotes.in
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23 There are three types of comments in java:
1) Single Line Comment: Single Line comment is use to add single
line description for your code. It is easy to use. Single Line comment start
with two forwordslashes (//). Any statement written in front of this slash is
not executed by compiler.
Syntax: // this is single line comment
2) Multi Line Comment: Multi Line comment is use to comment
multiple lines of code. It is mostly used to provide explanation about
particular m ethod or your program. Multi line comments start with /* and
ends with */. The statements written inside these comments are ignore by
the compiler and interpreter.
Syntax: /* This is multiline comment
This part is not executed.
This will be used to provide description about the program.
*/
Example: class Comment Example
{
public static void main(String arg[])
{
/* In this example, we will learn how to create variables and
How to display value of variable on output screen. */
double a =4.6755; // we have created variable here
System.out.print("Variable a:" + a);
}
}
3) Documentation Comment: This type of comment is used
produced an HTML file that documents your program. These comments
are usually used to write a code for project or software application, since it
helps to generate documentation page for reference, which can be used for
getting information about present methods, classes and arguments etc.
Documentation comments start with /** and ends with */.
Syntax:
/** Comment start
*You can used various tag to specify a parameters or method or heading
*we can use various HTML tags here.
*
*/ munotes.in
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24
1.18 BRACES AND CODE BLOCK
Curly Braces {}: Used to defined values of during array initialization. It is
also used to defined block of code for classes, interface. Method and
constructor bodies also enclosed in curly braces. Braces are used to group
statements in an if statement, a loop and other c ontrol statements.
Example: class Example3
{
//statements
}
Brackets []: It is used to declare array type. It is also used to access
individual elements from array list. And dereferencing array values.
Parentheses (): It is used to declare method an d constructor. It is used to
provide parameters in method definition and invocation. It is also used to
defined order of operation in expression.
1.19 VARIABLES AND VARIABLE NAME
Variable is the basic unit of storage in java program. It is like a
container which holds value while java program is executed. A variable is
the name given to a memory location. A variable is assigned with data
type. A value stored in variable can be changed during program execution.
A variable can be defined b y the combination of an identifier, a type and
an option initializer. All the variables have a scope, which defines their
visibility and the lifetime.
Syntax for Variable Declaration:
Type identifier; // variable declaration only
Type identifier = valu e; // variable with initialization
Here, type defines what type of data is stored in this variable. It defines
data type of variable. Identifier is the name of the variable. You can
initialize variable by assigning equal sign after name of variable.
Few Examples of variable declaration:
int a, b, c; // declaring three int variables
int d=3, e; // declaring two int variable and initializing one int variable d
double d=3.14; // declaring and initializing double variable
char c=’a’; //declaring and initia lizing char variable
There are three types of variables you can create in java.
1) Local variable: The variable declare inside the body of method or
constructor is called local variable. Scope of local variable exists only
within the block where it is decla red. We can access variable only munotes.in
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25 within same block. You cannot able to use local variable outside of
that method.
2) Instance Variable: Variable which is declare inside the class and
outside the method is called as instance variable. Instance variables are
created when an object of class is created and destroyed when object
get destroyed. Value of instance variable is instance specific. You can
use access specifier to defined scope of instance variable. According to
defined access specifier visibility and lifet ime of this variable get
changed.
3) Static Variable: A variable that is declared with static keyword is
called static variable. This variable is also declared inside the class.
For static variable, memory allocated only once when class is loaded
in the me mory. Like instance variable static variable is not instance
specific. Static variable is created when you want to share same value
among all objects of the class. Means Value of static variable is similar
for all objects of class.
Programs:
1) Write a java program to find out area of triangle.
class Triangle
{
public static void main(String arg[])
{
Double pi= 3.14, r = 3, area;
area = 3.14*r*r;
System.out.print("Area of Triangle" + area);
}
}
Output:
Area of Triangle: 28.26
2) Program to calculate simple Interest
public class SimpleInterest
{
public static void main(String args[])
{
float p =2000, r = 6, t =3, sinterest;
//simple interest formula (principal* rate of interest * time
period)/100
sinterest = (p * r * t) / 100;
System.out.print("Simple Interest is: " +sinterest);
}
} munotes.in
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26 Output:
Simple Interest is: 360.0
1.20 SUMMARY
In this chapter, we learn introduction to java language, features of
java, Java virtual machine, Java Runtime Environment, Java Development
Kit, Lambda Expression, Method References, Writing and executing java
programs, identifiers, keywords, java API and variables with examples.
1.21 LIST OF REFERENCES
Java, A Beginner’s Guide, Eighth Edition, Herbert Schildt, McGraw Hill
Publisher
Java: The Complete Refe rence, Eleventh Edition, Herbert Schildt,
McGraw Hill Publisher
1.22 BIBLIOGRAPHY
https://www.javatpoint.com/java -tutorial
https://www.geeksforgeeks.org/java
https://www.beginnersbook.com/java -tutorial -for-beginners -with-
examples/
http://www.programiz.com/java -programmi ng/
https://docs.oracle.com/javase/tutorial/
1.23 MODEL QUESTIONS
1) Which component is used to compile, debug and execute java program?
a) JVM
b) JRE
c) JDK
d) JIT
2) Which component is responsible for converting bytecode into machine
specific code?
a) JVM
b) JRE
c) JDK
d) JIT
3) What is extension of java byte code?
a) .txt
b) .class
c) .java
d) .js munotes.in
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27
4) JRE stand for?
a) Java Runnable Environment
b) Java Runtime Environment
c) Java Runtime Extension
d) None of the above
5) ____ are the reserved words in java?
a) Keywords
b) Variables
c) Identifiers
d) All of the above
6) _____ is a sequence of one and more characters?
a) Identifiers
b) Keywords
c) Variables
d) Literals
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2
DATA TYPES
Unit Structure
2.0 Objective
2.1 Introduction
2.2 Primitive Data Types
2.3 Object Reference Types
2.4 Strings
2.5 Auto Boxing and Unboxing
2.6 Operators and Properties of Operators
2.6.1 Arithmetic Operators
2.6.2 Assignment Operators
2.6.3 Increment and Decrement Operators
2.6.4 Relational Operators
2.6.5 Logical Operators
2.6.6 Bitwise Operators
2.6.7 Conditional Operator
2.7 Summary
2.8 List of References
2.9 Bibliography
2.10 Model Questions
2.0 OBJECTIVE
In this chapter, you will be going to learn following topics:
Primitive data types supported in java.
Creating string in java using String class and diffe rent methods of
string class.
How to convert primitive type to object type.
Use of different types operators available in java.
2.1 INTRODUCTION
Data types and Operator are the main fundamental elements of java
Programming. In this chapter we will learn different data types supported munotes.in
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29 in java language. Java is strongly type language, which means that you
must need to declare variable before they can be used. This declaration
includes variable’s type and name. Data types defines type of value stored
in variable.
Another concept we will going to learn in this chapter is operators
and types of operators supported in java. Java provide a rich set of
operators. Java supports all basic operators and some additional operators
for handing special condition.
2.2 PRIMITIVE DATA TYPES
Data Types: When you define a variable in java, you must need to defined
what kind of value that variable will stored. This wi ll be defined with the
help of data types. Based on this information compiler will decide how
much space to allocate in the memory for the variable.
Java programming language defines eight primitive data types: byte,
short. int, float, double, char, bool ean. A primitive type is predefined in
java language. Primitive types are the most basic data types available in
java. Size of these primitive data type is fixed; it does change from one
operating system to another. This primitive type can be placed into f our
group.
Integers: This group includes byte, short, int and long, which represents
whole numbers. All these integers support signed, positive and negative
values.
Floating - point numbers: This group include float and double data type,
which represents numbers with fractional value. Floating point numbers
are used when evaluating expression that require fractional precision.
Character: this group include char data type.
Boolean: This group include Boolean data type, which includes binary
value like true/false.
Data Type Size Default value
byte 1 byte 0
short 2 byte 0
int 4 byte 0
long 8 byte 0
float 4 byte 0.0f
double 8 byte 0.0d
char 2 byte \u0000 munotes.in
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30 boolean 1 bit false
Fig. Primitive Data Types
byte:
It is a smallest integer type. The Byte data type is 8 bits (1 byte)
signed two’s complement integer. It has value range lies between -128 to
127. Its default value is zero.
Syntax of declaring byte variable:
byte variable1 ;
short:
It is a signed 16 bits (2 byte) two’s complement integer. It has value
range lies between -32,768 to 32,767. Its default value is zero.
Syntax:
short t, s;
int:
The int data type is 32 bits (4 bytes) signed two’s complement
integer. It has the value range lies between - (2 31)to (231 -1). Its default
value is zero. It is most commonly used data type.
Syntax:
int a, b;
int c=2;
long:
The long data type is 64 bits (8 byte) signed two’s complement
integer. It has value range lies between – (263) to (263-1). Its default value
is zero.
Example:
class DataTypesExample1
{
public static void main(String arg[])
{
byte b = -100;
short num = 150;
int a = 1;
long l = 4562455555555L;
System.out.println("Byte Value :" + b);
System.out.prin tln("Integer Value:" + a );
System.out.println(" Int value: " + a );
System.out.println("Long value: " + l );
}
}
Output:
Byte Value : -100
Integer Value:1
Int value: 1 munotes.in
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31 Long value: 4562455555555
float:
The float data type is single precision 32 bits (4 byte) floating point.
It is useful for storing smaller precision but not suited for large degree of
precision. Its default value is 0.0f.
Syntax:
Float f = 3.14f, a;
double :
The double data type is double precision 64 bits (8 byte) floating
point. I t is useful for storing floating point values with large precision. Its
default value is 0.0d.
Syntax:
double d = 45.78521457;
char:
The char is 16 bits (2 byte) Unicode character. It has the value range
lie between 0 to 65,535. This data type is used to stored characters.
Unicode defines a fully international character set that can represents
all of the characters that are available in all human languages. Its default
value is ‘ \u0000’.
Syntax:
char c = ‘g’;
Boolean:
The Boolean data type is used to stored logical value. It stores only
two possible values: true and false. It represents only one bit of
information. Values of Boolean variable can not be converted into any
other type. Its default value is false.
Example:
class Da taTypesExample2
{
public static void main(String arg[])
{
float f = 22.14f;
double d = 12.11122452;
char c='g';
boolean flag = true;
System.out.println("float value:" + f);
System.out.println("double value:" +d);
System.out.println("Char value:"+ c);
System.out.println("boolean value:"+ flag);
} munotes.in
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32 }
Output:
float value:22.14
double value:12.11122452
Char value:g
booleanvalue:true
2.3 OBJECT REFERENCE TYPES
In java, not - primitive data type is also known as object reference
type. Java object refer ence type holds the references of dynamically
created class objects and provide a means to access those objects stored in
memory. For example, if you have created class Example and you have
created its object d, then d is called as object reference type. All the
reference types are subclass of type java.lang.Object. Object reference
type includes class, Annotation, Array, Enumeration and Interface. Like
primitive data type it is not predefined.
Reference
Type Description
Class Class is a collection of objects. You can create multiple
objects of class.
Annotation It provides a way to associate metadate with program
elements.
Array It provides a data structure that stores the elements of
similar type.
Enumeration A reference to a set of objects that re presents a related
set of choices.
Interface It is implemented by java classes. interface provides you
collection of abstract methods.
Fig. Object Reference Types
2.4 STRINGS
Java String is an object that represents a sequence of characters.
String class is used to create string object in java. It is defined in java.lang
package. Java string is immutable. Once string is created, you cannot able
to change its value.
There are two ways to create string in java:
1) Using String Literal
Examples: String name = “Amit”;
String address = “thane”;
munotes.in
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33 2) Using new keyword
Examples: String s1 = new String(“Welcome”);
String s2 = new String(“we are learning java programming”);
Program:
class StringExample
{
public static void main(String arg[])
{
//creating string using string literal
String name = "Kunal";
System.out.println("Name: " + name);
//creating string using new keyword
String s = new String("java is easy to learn ");
System.out.println(s);
}
}
Output:
Name: Kunal
Java is easy to learn
String class also provides you lots of methods to perform different
operations on string.
List of Methods:
Method Description
toUpperCase(String str) Convert the given string in uppercase.
toLowerCase(String str) Convert the given string in lowercase.
startWith(String prefix) Test if given string starts with specified
prefix. True or false result.
endsWith(String Suffix) Test if given string ends with specified
suffix . Return true or false result.
charAt(int index) Return the character value for specified
index number.
length() Return the length of this string.
substring(int beginindex) Return new string that is substring of the
given string.
replace() Used to replace all the occurrences of old
char in this string with new char.
contains(CharSequence s) Return true or false after matching specified munotes.in
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34 character sequence in given string.
indexOf(int ch) Return the index value of specified char.
equals(String str) Compares the given string with this
specified string. Return true or false result.
trim() Use to remove leading and trailing
whitespaces in this string.
valueOf(int value)
valueOf(float value)
valueOf(double value)
valueOf(long value) Used to convert gi ven type to string.
concat(String str) Concatenates specified string at the end of
this string.
Example:
class StringMethods
{
public static void main(String arg[])
{
String s="java programming";
String s1= " PYTHON";
System.out.pr intln("Upper Case : " + s.toUpperCase());
System.out.println("Lowercase : " +s1.toLowerCase());
System.out.println("Trim : " + s.trim());
System.out.println( "Start With : " + s.startsWith("Sa"));
System.out.println("Ends with: " + s.endsWith("g "));
System.out.println("Char at: " + s.charAt(3));
System.out.println( "length: " + s.length());
System.out.println("substring : " +s.substring(2,4));
String r=s.replace("java","python");
System.out.println(r);
System.out.println("Contains: " + r.contains("java"));
int index1=s.indexOf("a");
System.out.println("Index OF : " + index1);
int index2=s.lastIndexOf('g');
System.out.println("last Index of: " + index1);
String str1 = "Hello";
String str2 = "Javatpoint";
// Concatenating one string munotes.in
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35 String str4 = str1.concat("javatpoint");
System.out.println(str4);
}
}
Output:
Upper Case : JAVA PROGRAMMING
Lowercase : python
Trim : java programming
Start With : false
Ends with: true
Char at: a
length: 16
substring :va
python programming
Contains: false
Index OF : 1
last Index of: 1
Hellojavatpoint
2.5 AUTOBOXING AND UNBOXING
Autoboxing:
The Automatic conversion of primitive type into its corresponding
wrapper class type is called Autoboxing. For example, converting an int to
an Integer. Converting an float to Float type.
Unboxing:
The automatic conversion of object of wrapper type into its
corresponding primitive type is called as unboxing. For example,
converting Integer object into int type, Double object into double type.
List of primitive type and their corresponding wrapper type:
Primitive Type (Data Types) Wrapper Type (Classes)
byte Byte
short Short
int Int
long Long
float Float
double Double
char Char
boolean Boolean
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36
Example:
class AutoboxingEx
{
public static void main(String arg[])
{
int a=20;
Integer n1 = new Integer(a); // autoboxing
Integer n2 = a; //autoboxing
System.out.println("n1 : " +n1);
System.out.println( "n2: " + n2);
Integer n3 = new Integer(50); //unboxing
int b = n3;
System.out.print("b: " +b);
}
}
Output:
n1 : 20
n2: 20
b: 50
2.6 OPERATORS AND PROPERTIES OF OPERATORS
Operators are used to performed some mathematical and logical
operations. Java provides a rich set of operators. All basic operators are
classified into four types; relational, arithmetic, logical and bitwise. It also
provides you some additional operators like conditional operator,
assignment operator and increment and decrement operator.
2.6.1 Arithmetic Operators
Arithmetic operators are used to perform operations like addition,
subtraction, multiplication and division. These are the basic mathematical
operator.
List of arithmetic operators:
Operators Description
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulus division
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37
Example:
class ArithmeticOperator
{
public static void main(String arg[])
{
double a=20, b=4;
System.out.println("Addition: " + (a+b));
System.out.println("Subtraction: " + (a -b));
System.out.println("Multiplication: " + (a*b));
System.out.println("Division: " + (a/b));
System.out.println("Modulus: " + (a%b));
}
}
Output:
Addition: 24.0
Subtraction: 16.0
Multiplication: 80.0
Division: 5.0
Modulus: 0.0
2.6.2 Assignment Operators
Assignment operator is one of the most common operators; you are
using in java program. It is used to assign value on its right to the operand
(variable) on its left.
Symbol: =
Example: int a = 4;
double d = 3.2;
Compound Assignment Operators:
Operat or Description
+= Addition Assignment: It work by adding the current value
of the variable on left to the value on the right and then
assign result to the operand on the left.
-= Subtraction Assignment: It work by subtracting the
current value of the variable on left to the value on the right
and then assign result to the operand on the left. munotes.in
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38 /= Division Assignment: It work by dividing the current value
of the variable on left to the value on the right and then
assign result to the operand on the left.
*= Multiplication Assignment: It work by multiplying the
current value of the variable on left to the value on the r ight
and then assign result to the operand on the left.
%= Modulus Assignment: It work by dividing the current
value of the variable on left to the value on the right and
then assign remainder to the operand on the left.
Program:
class AssignmentOperator
{
public static void main(String arg[])
{
int num = 60; // simple asignment operator
double a=20, b=30;
a += 10; // it is similar to the expression a= a+10
b -= 5; // it is similar to b= b -5;
System.out.println(" As signment operator: " + num);
System.out.println("Addition Assignment: " + a);
System.out.println("Subtraction Assignment: " + b);
}
}
Output:
Assignment operator: 60
Addition Assignment: 30.0
Subtraction Assignment: 25.0
2.6.3 Increment and Decrement Operators
Increment operator is used to increase value of operand by one.
Decrement operator is used to decrease value of operand by one. Both
operators required only one operand.These operators can be used in either
prefix and pos tfix form. In prefix form, the operand is incremented and
decremented before the value is obtain for used in the expression. In
postfix form, the operand is incremented and decremented after the value
is obtain for used in the expression.
Operator Descrip tion
++ Increment Operator
-- Decrement Operator
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39 Program:
class Operator
{
public static void main(String arg[])
{
int num1 = 20, num2 = 10;
System.out.println(num1++); // num1++ is post -increment
System.out.println(++num1); // ++num1is pri -increment
System.out.println(num2 --); //it is post -decrement
System.out.println( --num2); // it is pri -decrement
}
}
Output:
20
22
10
18
Relational Operators
Relational operators are used to determine relationship between two
variables, like value of one operand is greater then, equal to or less than
another operand. The relational operator generates true and false result.
Operator Description
== Equal to
!= Not equal to
> Greater than
< Less than
>= Greater than and equal to
<= Less than and equal to
Fig. Relational Operators
Program:
class Relationaloperator
{
public static void main(String arg[])
{
int a=10, b=30, c=20;
System.out.println("a System.out.println("a>b :" + (a>b));
System.out.println("a==b :" +(a==b));
System.out.println(" a!=b : " + (a!=b));
}
} munotes.in
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40 Output:
aa>b :false
a==b :false
a!=b : true
2.6.4 Logical Operators
Logical operators are used to perform logical AND, OR and NOT
operation. Its function is similar to AND gate, OR gate and NOT gate in
digital electronics. Logical AND gate return true result if both the
expressions are true. Logical OR gate return true result if either one
expression is true. Logical Not r eturn true if expression is false and vice
versa.
Operator Description
&& Logical AND
|| Logical OR
! Logical NOT
Fig. Logical Operators
Program:
class LogicalOperator
{
public static void main(String arg[])
{
int a=10, b=30, c=20;
System.out.println("Logical AND: " + (a System.out.println("Logical OR: " + (a>c || a System.out.println("Logical OR: " + (a>c && a System.out.print("Logical NOT:" + !(a>b));
}
}
Output:
Logical AND: true
Logical OR: true
Logical OR: false
Logical NOT:true
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41 2.6.5 Bitwise Operators
Bitwise operators operate on binary value. It returns result by
performing manipulation on individual bit of a number. In Bitwise OR
operation, it performs bit by bit OR operation of input value and it return 1
if either of the bits is 1 otherwise it returns 0.
In bitwise AND operation, it performs bit by bit AND operation of
input value and it return 0 if either of the bits is 0 otherwise it returns 1.
In bitwise XOR operation, it performs bit by bit XOR operation of
input value and it return 1 if corresponding bits different, else it gives zero
if bits are same. Bitwise Complement operator returns one’s complement
of input value.
Operator Description
& Bitwise AND
| Bitwise inclusive OR
^ Bitwise Exclusive OR
~ Bitwise Complement
Program:
class BitwiseOperator
{
public static void main(String arg[])
{
int a=5, b=12;
System.out.println("Bitwise AND: " + (a&b) );
System.out.println("Bitwise Inclusive OR: " + (a|b) );
System.out.println(" Bitwise Exclusive OR: " + (a^b));
System.out.print("Bitwise Complement:" + (~a));
}
}
Output:
Bitwise AND: 4
Bitwise Inclusive OR: 13
Bitwise Exclusive OR: 9
Bitwise Complement: -6
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42 2.6.6 Conditional Operator
Operator Description
&& Logical or Conditional AND
|| Logical or Conditional OR
?: Ternary operator
Ternary operator is similar to If -then-else statement in java. A
ternary operator evaluates the test condition and execute the block of code
based on result of the condition.
Syntax: condition ? expression1 : expression2
It first checks the test condition and execute expression1 if
condition is true, else it execute expression2.
Program:
class TernaryOperator
{
public static void main(String args[])
{
int marks=40;
String result = (marks>40) ? "PASS" : "FAIL";
System.out.print(result);
}
}
Output:
FAIL
2.7 SUMMARY
In this chapter, we learn primitive data types, object reference types,
creating string in java and different methods of string clas s, converting
primitive date type to object type and vice -versa, operators and their
different types.
2.8 LIST OF REFERENCES
Java, A Beginner’s Guide, Eighth Edition, Herbert Schildt, McGraw Hill
Publisher
Java: The Complete Reference, Eleventh Edition, Herbert Schildt,
McGraw Hill Publisher munotes.in
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43 2.9 BIBLIOGRAPHY
https://www.javatpoint.com/java -tutorial
https://www.geeksforgeeks.org/java
https://www.beginnersbook.com/java -tutorial -for-beginners -with-
examples/
http://www.programiz.com/java -programming/
https://docs.oracle.com/javase/tutorial/
2.10 MODEL QUESTIONS
1) How many primitive types are there in java?
a) 5
b) 6
c) 7
d) 8
2) Size of int type in java?
a) 8 bit
b) b) 4 bit
c) 16 bit
d) d) 32 bit
3) The smallest integer type is ___ and its size is ___ bits.
a) short, 16
b) byte, 16
c) short, 8
d) byte, 8
4) which of the following is a symbol of assignment operator?
a) ==
b) =
c) !
d) ~
5) Size of double data type in java?
a) 4 byte
b) 8 byte
c) 2 byte
d) 1 byte
6) What is the range of byte data type in java?
a) - 128 to 127
b) -128 to 128
c) -127 to 128
d) -127 to 127
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44 7) Increment operator increases value of operand by which value?
a) 2
b) 3
c) 1
d) 4
8) Which of the following is not conditional operator?
a) &&
b) ||
c) ?:
d) ~
9) What is the size of short data type in java?
a) -128 to 127
b) -32768 to 32767
c) – (231) to (231-1)
d) None of this
10) In java, byte, short, int and long all of these are ____ integers.
a) Signed
b) Unsigned
c) Both of the above
d) None of the above
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45Unit II
3
CONTROL STATEMENTS
Unit Structure
3.1 Introduction
3.2 Java Control Statements
3.2.1. Decision -Making statements
3.2.2. If Statement
3.2.3. if -else statement
3.2.4.if -else-if ladder
3.2.5. Nested if -statement
3.3. Switch Statement
3.4.Jump Statements
3.4.1. Java for loop
3.4.2. Java for -each loop
3.4.3. Java while loop
3.4.4. Java do -while loop
3.4.5. Jump Statements
3.4.5.1. Java break statement
3.4.5.2. Java continue statement
3.5. Summary
3.6. List of References
3.7. Questions
3.1. INTRODUCTION
Java compiler executes the code through and through. The
assertions in the code are executed by the request where they show up.
Nonetheless, Java gives proclamations that can be utilized to control the
progression of Java code. Such proc lamations are called control stream
explanations. It is one of the crucial components of Java, which gives a
smooth progression of program.
3.2. JAVA CONTROL STATEMENTS
In Java, program is a bunch of articulations and which are executed
consecutively all together in which they show up. In that assertions, somemunotes.in
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46estimation have need of executing for certain conditions and for that we
need to give control to that assertions. All in all, Control explanations are
utilized to furnish the progression of execu tion with condition. In this unit,
we will gain proficiency with the control structure exhaustively. Java
provides three types of control flow statements.
Decision Making statements
if statements
switch statement
Loop statements
do while loop
while loop
for loop
for-each loop
Jump statements
break statement
continue statement
3.2.1. Decision -Making statements:
As the name recommends, dynamic proclamations choose which
articulation to execute and when. Dynamic articulations assess the
Boolean articulation and control the program stream contingent on the
consequence of the condition gave. There are two sorts of dynamic
explanations in Java, i.e., If articulation and switch proclamation.
3.2.2. If Statement
In Java, the "if" articulation is util ized to assess a condition. The
control of the program is redirected relying on the particular condition.
The state of the If articulation gives a Boolean worth, either obvious or
bogus. In Java, there are four kinds of if -proclamations given underneath.
Simple if statement
if-else statement
if-else-if ladder
Nested if -statement
Let's understand the if -statements one by one.
Simple if statement:
It is the most basic statement among all control flow statements in
Java. It evaluates a Boolean expression and enables the program to enter a
block of code if the expression evaluates to true.munotes.in
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47
Syntax of if statement is given below.
if(condition) {
statement 1;//executes when condition istrue
}
Statement -a;
In proclamation block, there might be single explanation or various
articulations. Assuming the condition is valid, articulation square will be
executed. Assuming the condition is bogus, proclamation square will
preclude and articulation a will be executed. Consider the accompanying
model wher ein we have utilized the if articulation in the java code.
1)Student.java
public class Student {
public static void main(String[] args) {
intx=10;
inty=12;
if(x+y >20)
{
System.out.println( "x+yisgreater than 20");
}
}
}
Output:
x + y is greater than 20munotes.in
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483.2.3. if -else statement
Theif-else statement is an extension to the if -statement, which
uses another block of code, i.e., else block. The else block is executed if
the condition of the if -block is evaluated as false.
Following figure shows the flow of statement.
Syntax:
if(condition) {
statement 1;//executes when condition istrue
}
else{
statement 2;//executes when condition isfalse
}
Statement -a;
If the condition is true then True -statement block will be
executed. If the condition is false then False -statement block will
beexecuted. In both cases the statement -a will always executed.
Consider the following example.
1)Student .java
public class Student {
public static void main(String[] args) {
intx=10;
inty=12;
if(x+y <10)munotes.in
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49{
System.out.println( "x+yislessthan 10");
}
else{
System.out.println( "x+yisgreater than 20");
}
}
}
Output:
x+ y is greater than 20
2) write a program to check whether the number is divisible by 2 or
not.
import java.io.*;
classdivisorDemo
{
public static void main(String[ ] args)
{
int a =11;
if(a%2==0)
{
System.out.println(a +" is divisible by 2");
}
else
{
System.out.println(a+" is not divisible by 2");
}
}
}
Output:
11 is not divisible by 2
3.2.4. if-else-if ladder
The if -else-if explanation contains the if -articulation followed by
different else -if proclamations. At the end of the day, we can say that it is
the chain of if -else articulations that make a choice tree where the program
might enter in the square of code where the condition is valid. We can
likewise characterize an else explanation toward the finish of the chain.
Syntax of if -else-if statement is given below.
if(condition 1)
{munotes.in
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50statement 1;//executes when condition 1istrue
}
elseif(condition 2)
{
statement 2;//executes when condition 2istrue
}
else{
statement 2;//executes when alltheconditions arefalse
}
Consider the following example.
1)Student.java
public class Student {
public static void main(String[] args) {
String city="Delhi";
if(city =="Meerut")
{
System.out.println("city ismeerut");
}
elseif(city =="Noida")
{
System.out.println( "city isnoida");
}
elseif(city =="Agra")
{
System.out.println("city isagra");
}
else
{
System.out.println(city);
}
}
}
Output:
Delhi
3.2.5. Nested if -statement
In nested if -statements, the if statement can contain a iforif-
elsestatement inside another if or else -if statement.munotes.in
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51
Syntax of Nested if -statement is given below.
if(condition 1){
statement 1;//executes when condition 1istrue
if(condition 2){
statement 2;//executes when condition 2istrue
}
else{
statement 2;//executes when condition 2isfalse
}
}
statement 4;
If the condition1 is true then it will be goes for condition2. If the
condition2 is true then statement block1 will be executed otherwise
statement2 will be executed. If the condition1 is false then statement
block3 will be executed. In both cases the statement4 will always
executed.
Consider the following example.
1)Student.java
public class Student {
public static void main(String[] args) {
String address ="Delhi, India" ;
if(address.endsWith( "India" ))
{munotes.in
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52if(address.contains( "Meerut" ))
{
System.out.println( "Your cityisMeerut" );
}
elseif(address.contains( "Noida" ))
{
System.out.println( "Your cityisNoida" );
}
else
{
System.out.println(address.split( ",")[0]);
}
}
Else
{
System.out.println( "You arenotliving inIndia" );
}
}
}
Output:
Delhi
3.3. SWITCH STATEMENT:
In Java, Switch articulations are like if -else-if explanations. The
switch explanation contains various squares of code called cases and a
solitary case is executed dependent on the variable which is being
exchanged. The switch proclamation is simpler to u se rather than if -else-if
explanations. It likewise improves the intelligibility of the program.
Focuses to be noted with regards to switch proclamation:
The case factors can be int, short, byte, roast, or list. String type is
likewise upheld since rend ition 7 of Java
Cases can't be copy
Default explanation is executed when any of the case doesn't
coordinate with the worth of articulation. It is discretionary.
Break explanation ends the switch block when the condition is fulfilled.
It is discretionary, if not utilized, next case is executed.
While utilizing switch proclamations, we should see that the case
articulation will be of a similar kind as the variable. Nonetheless, it will
likewise be a consistent worth.munotes.in
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53The syntax to use t he switch statement is given below.
switch (expression){
casevalue1:
statement block1;
break ;
casevalue 2:
statement block 2;
break ;
casevalue 3:
statement block 3;
break ;
.
.
.
casevalueN:
statementN;
break ;
default :
default statement;
}
The condition is byte, short, character or a number. value1,value -
2,value -3,… are steady and is called as marks. Every one of these qualities
be inimitable or special with the assertion. Proclamation block1,
Articulation block2, Explanation block3,..are rundown of explanations
which contain one articulation or more than one proclamations. Case mark
is consistently end with ":" (colon).
Consider the following example t o understand the flow of the
switch statement.
1)Student.java
public class Student implements Cloneable
{
public static void main(String[] args)
{
intnum =2;
switch (num)
{
case0:
System.out.println( "number is0");
break ;munotes.in
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54case1:
System.out.println( "number is1");
break ;
default :
System.out.println(num);
}
}
}
Output:
2
While utilizing switch articulations, we should see that the case
articulation will be of a similar kind as the variable. Be that as it may, it
will likewise be a steady worth. The switch allows just int, string, and
Enum type factors to be utilized.
Program: write a program for bank account to perform following
operations.
-Check balance
-withdraw amount
-deposit amount
1)For example:
import java.io.*;
classbankac
{
public static void main(String args[]) throws Exception
{
intbal=20000;
intch=Integer.parseInt(args[0]);
System.out.println("Menu");
System.out.println("1:check balance");
System.out.println("2:withdraw amount... plz enter choiceand amount");
System.out.println("3:deposit amount... plz enter choiceand amount");
System.out.println("4:exit");
switch(ch)
{
case 1:
System.out.println("Balance is:"+bal);
break;
case 2:
int w=Integer.parseInt(args[1]);
if(w>bal)munotes.in
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55{
System.out.println("Not su fficient balance");
}
bal=bal -w;
System.out.println("Balance is"+bal);
break;
case 3:
int d=Integer.parseInt(args[1]);
bal=bal+d;
System.out.println("Balance is"+bal);
break;
default:
break;
}
}
}
Output:
Menu
1:check balance
2:withdraw amount... plz enter choice and amount
3:deposit amount... plz enter choice and amount
4:exit
Balance is:20000
3.4. LOOP STATEMENTS
In programming, now and again we need to execute the square of
code more than once while some condition assesses to valid. Be that as it
may, circle explanations are utilized to execute the arrangement of
guidelines in a rehashed request. The execution of the arrangement of
directions relies on a specific condition.
In Java, we have three kinds of circles that execute also.
Notwithstanding, there are contrasts in their grammar and condition really
looking at time.
for loop
while loop
do-while loop
Let's u nderstand the loop statements one by one.munotes.in
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563.4.1. Java for loop
In Java, for circle is like C and C++. It empowers us to introduce
the circle variable, actually look at the condition, and addition/decrement
in a solitary line of code. We utilize the for circle just when we precisely
know the occasions, we need to execute the square of code.
for(initialization, condition, increment/decrement)
{
//block ofstatements
}
The flow chart for the for -loop is given below.
Consider the following ex ample to understand the proper
functioning of the for loop in java.
1)Calculation.java
public class Calculattion
{
public static void main(String[] args)
{
//TODO Auto -generated method stub
intsum=0;
for(intj=1;j<=10;j++)
{
sum=sum+j;
}
System.out.println( "The sumoffirst10natural numbers is"+sum);
}
}
Output:
The sum of first 10 natural numbers is 55
3.4.2. Java for -each loop
Java gives an improved to circle to navigate the information
structures like exhibit or assortment. In the for -each circle, we don't havemunotes.in
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57to refresh the circle variable. The linguistic structure to utilize the for -each
circle in java is given beneath.
for(data_type var:array_name/collection_name)
{
//statements
}
Consider the following example to understand the functioning of the for -
each loop in Java.
1)Calculation.java
public class Calculation
{
public static void main(String[] args)
{
//TODO Auto -generated method stub
String[] names ={"Java" ,"C","C++" ,"Python" ,"JavaScript" };
System.out.println( "Printing thecontent ofthearray names: \n");
for(String name:names)
{
System.out.println(name);
}
}
}
Output:
Printing the content of the array names:
Java
C
C++
Python
JavaScript
3.4.3. Java while loop
The while circle is likewise used to emphasize over the quantity of
explanations on numerous occasions. Notwithstanding, in the event that
we don't have the foggiest idea about the quantity of emphasess ahead of
time, it is prescribed to utilize some time circle. Not at all like for circle,
the instatement and addition/decrement doesn't occur inside the circle
proclamation in while circle.
It is otherwise called the passage controlled circle since the
condition is checked toward the beginning of the circl e. On the off chance
that the condition is valid, the circle body will be executed; any other way,
the assertions after the circle will be executed.munotes.in
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58The grammar of the while circle is given underneath.
while (condition)
{
//looping statements
}
The flow chart for the while loop is given in the following image.
Consider the following example.
Calculation .java
public class Calculation {
public static void main(String[] args) {
//TODO Auto -generated method stub
inti=0;
System.out.println( "Printing thelistoffirst10even numbers \n");
while (i<=10)
{
System.out.println(i);
i=i+2;
}
}
}munotes.in
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59Output:
Printing the list of first 10 even numbers
0
2
4
6
8
10
3.4.4. Java do -while loop
The do -while circle really takes a look at the condition toward the
finish of the circle subsequent to executing the circle explanations. At the
point when the quantity of cycle isn't known and we need to execute the
circle once, we can utilize do -while ci rcle.
It is otherwise called the exit -controlled circle since the condition
isn't checked ahead of time. The sentence structure of the do -while circle
is given beneath.
do
{
//statements
}while (condition);
The flow chart of the do-while loop is given in the following image.
Consider the following example to understand the functioning of
the do -while loop in Java.munotes.in
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601)Calculation.java
public class Calculation
{
public static void main(String[] args)
{
//TODO Auto -generated method stub
inti=0;
System.out.println("Printing thelistoffirst10even numbers \n");
do
{
System.out.println(i);
i=i+2;
}while (i<=10);
}
}
Output:
Printing the list of first 10 even numbers
0
2
4
6
8
10
3.4.5. Jump Statements
Hop articulations are utilized to move the control of the program to
the particular assertions. At the end of the day, bounce articulations move
the execution control to the next piece of the program. There are two kinds
of hop proclamations in Java, i.e., break and proceed.
3.4.5.1. Java break statement
As the name recommends, the break proclamation is utilized to
break the current progression of the program and move the con trol to the
following assertion outside a circle or switch explanation. Be that as it
may, it breaks just the inward circle on account of the settled circle.
The break articulation can't be utilized autonomously in the Java
program, i.e., it must be comp osed inside the circle or switch explanation.
The break statement example with for loop
Consider the following example in which we have used the break
statement with the for loop.
1)BreakExample.java
public class Break Example
{munotes.in
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61public static void main(String[] args)
{
//TODO Auto -generated method stub
for(inti=0;i<=10;i++)
{
System.out.println(i);
if(i==6){
break ;
}
}
}
}
Output:
0
1
2
3
4
5
6
break statement example with labeled for loop
1)Calculation.java
public class Calculation {
public static void main(String[] args)
{
//TODO Auto -generated method stub
a:
for(inti=0;i<=10;i++) {
b:
for(intj=0;j<=15;j++) {
c:
for(intk=0;k<=20;k++) {
System.out.println(k);
if(k== 5){
break a;
}
}
}
}
}
}munotes.in
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62Output:
0
1
2
3
4
5
3.4.5.2. Java continue statement
Unlike break statement, the continue statement doesn't break the
loop, whereas, it skips the specific part of the loop and jumps to the next
iteration of the loop immediately.
Consider the following example to understand the functioning of
the continue statement in Java.
public class Continue Example
{
public static void main(String[] args)
{
//TODO Auto -generated method stub
for(inti=0;i<=2;i++) {
for(intj=i;j<=5;j++) {
if(j==4)
{
continue ;
}
System.out.println(j);
}
}
}
}
Output:
0
1
2
3munotes.in
Page 63
635
1
2
3
5
2
3
5
3.5. SUMMARY:
In this Chapter, we covered control flow statement
InDecision -Making statements, we learned if, if -else,if -else-if ladder,
Nested if -statement, Switch Statement
In this chapter we study about Looping statement like for loop, for -
each loop, while loop, do -while loop, also jump statement break
statement, continue statement.
3.6. LIST OF REFERENCES
1. Java 2: The Complete Reference, Fifth Edition, Herbert Schildt, Tata
McGraw Hill.
2. An Introduction to Object oriented Programming with JAVA, C
THOMAS WU3. www.javatpoint.com
3.7. QUESTION
1)What mean by Decision control statement?
2)Explain If Else statement with suitable example.
3)Explain Nested if statement with suitable example.
4)Explain loop control statement
5) What is mean by switch control statement with example.
6) Explain loop control statement with example.
munotes.in
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64 4
CLASSES
Unit Structure
4.1 Objective
4.2 C lass
4.2.1 Creating “main” in a separate class
4.2.2 Methods with parameters
4.2.3 Methods with a Return Type
4.2.4 Method Overloading
4.2.5 Passing Objects as Parameters
4.2.6 Passing Values to methods and Constructor:
4.2.7 Abstract Classes
4.2.8 Extending the class:
4.3 Summary
4.4 List of reference s
4.5 Questions
4.1 OBJECTIVE
In this lesson of Java Tutorial, you will learn...
How to create class
How to create method
How to create constructor
4.2 CLASS
Definition: A class is a collection of objects of similar type. Once a class
is defined, any number of objects can be produced which belong to that
class.
Class Declaration
classclassname
{
…
ClassBody
…
}
Objects are instances of the Class. Classes and Objects are v ery much
related to each other. Without objects you can't use a class. munotes.in
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65 A general class declaration:
class name1
{
//public variable declaration
voidmethodname()
{
//body of method…
//Anything
}
}
Now following example shows the use of method.
class Demo
{
privateintx,y,z;
public void input()
{
x=10;
y=15;
}
public void sum()
{
z=x+y;
}
public void print_data()
{
System.out.println(“Answer is =” +z);
}
public static void main(String args[])
{
Demo object=new Demo();
object.input();
object.sum();
object.print_data();
}
}
In program,
Demo object=new Demo();
object.input();
object.sum();
object.print_data();
In the first line we created an object. munotes.in
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66 The three methods are called by using the dot operator. When we call a
method the code inside its block is executed.
The dot operator is used to call methods or access them.
4.2.1 Creating “main” in a separate class
We can create the main method in a separate class, but during compilation
you need to make sure that you compile the class with the “main”
method.
class Demo
{
privateintx,y,z;
public void input() {
x=10;
y=15;
}
public void sum()
{
z=x+y;
}
public void print_data()
{
System.out.println(“Answer is =” +z);
}
}
classSumDemo
{
public static void main(String args[])
{
Demo object=new Demo();
object.input();
object.sum();
object.print_data();
}
}
Use of dot operator
We can access the variables by using dot operator.
Following program shows the use of dot operator.
classDotDemo
{
intx,y,z; munotes.in
Page 67
67 public void sum(){
z=x+y;
}
public void show(){
System.out.println("The Answer is "+z);
}
}
class Demo1
{
public static void main(String args[]){
DotDemo object=new DotDemo();
DotDemo object2=new DotDemo();
object.x=10;
object.y=15;
object2.x=5;
object2.y=10;
object.sum();
object.show();
object2.sum();
object2.show();
}}
output :
C:\cc>javac Demo1.java
C:\cc>java Demo1
The Answer is 25
The Answer is 15
Instance Variable
All variables are also known as instance variable. This is because
of the fact that each instance or object has its own copy of values for the
variables. Hence other use of the “dot” operator is to initialize the value of
variable for that instance.
4.2.2 Methods with parameters
Following program shows the method with passing parameter.
classprg
{
int n,n2,sum;
public void take(intx,int y)
{
n=x;
n2=y; munotes.in
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68 }
public void sum()
{
sum=n+n2;
}
public void print()
{
System.out.println("The Sum is"+sum);
}
}
class prg1
{
public static void main(String args[])
{
prgobj=new prg();
obj.take(10,15);
obj.sum();
obj.print();
}
}
4.2.3 Methods with a Return Type
At the point when technique return some worth that is the sort of
that strategy. For Instance: a few techniques are with boundary yet that
strategy didn't return any worth that implies kind of technique is void.
Furthermore, in the event that s trategy return whole number worth, the
sort of technique is a whole number.
Following program shows the method with their return type.
class Demo1
{
int n,n2;
public void take( intx,int y)
{
n=x;
n=y;
}
publicintprocess()
{
return (n+n2);
}
} munotes.in
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69 Class prg
{
public static void main(String args[])
{
int sum;
Demo1 obj=new Demo1();
obj.take(15,25);
sum=obj.process();
System.out.println("The sum is"+sum);
}
}
Output:
The sum is25
4.2.4 Method Overloading
Method overloading means method name will be same but each
method should be different parameter list.
class prg1
{
int x=5,y=5,z=0;
public void sum()
{
z=x+y;
System.out.println("Sum is "+z);
}
public void sum(inta,int b)
{
x=a;
y=b;
z=x+y;
System.out.println("Sum is "+z);
}
Public intsum(int a)
{
x=a;
z=x+y;
return z;
}
}
class Demo
{ munotes.in
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70 public static void main(String args[])
{
prg1obj=new prg1();
obj.sum();
obj.sum(10,12);
System.out.println(+obj.sum(15));
}
}
Output:
sum is 10
sum is 22
27
4.2.5 Passing Objects as Parameters
Objects can even be passed as parameters.
class para123
{
int n,n2,sum,mul;
public void take(intx,int y)
{
n=x;
n2=y;
}
public void sum()
{
sum=n+n2;
System.out.println("The Sum is"+sum);
}
public void take2(para123 obj)
{
n=obj.n;
n2=obj.n2;
}
public void multi()
{
mul=n*n2;
System.out.println("Product is"+mul);
}
}
classDemoPara
{ munotes.in
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71 public static void main(String args[])
{
para123ob=new para123();
ob.take(3,7);
ob.sum();
ob.take2(ob);
ob.multi();
}
}
Output:
C:\cc>javac DemoPara.java
C:\cc>java DemoPara
The Sum is10
Product is21
We have defined a method “take2” that declares an object named
obj as parameter. We have passed ob to our method. The method “take2”
automatically gets 3,7 as values for n and n2.
4.2.6 Passing Values to methods and Constructor:
These are two differ ent ways of supplying values to methods.
Classified under these two titles -
1.Pass by Value
2.Pass by Address or Reference
Pass by Value -When we pass a data type like int, float or any other
datatype to a method or some constant values like(15,10). They are all
passed by value. A copy of variable’s value is passed to the receiving
method and hence any changes made to the values do not affect the actual
variables.
class Demopbv
{
int n,n2;
public void get(intx,int y)
{
x=x*x; //Changing the values of pass ed arguments
y=y*y; //Changing the values of passed arguments
}
}
class Demo345
{
public static void main(String args[])
{ munotes.in
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72 inta,b;
a=1;
b=2;
System.out.println("Initial Values of a & b "+a+" "+b);
Demopbvobj=new Demopbv();
obj.get(a,b);
System.out.println( "Final Values "+a+" "+b);
}
}
Output:
C:\cc>javac Demo345.java
C:\cc>java Demo345
Initial Values of a & b 1 2
Final Values 1 2
Pass by Reference
Objects are always passed by reference. When we pass a value by
reference, the reference o r the memory address of the variables is passed.
Thus any changes made to the argument causes a change in the values
which we pass.
Demonstrating Pass by Reference ---
class Pass_by_ Ref
{
int n,n2;
public void get(inta,int b)
{
n=a;
n2=b;
}
public void doub leit(pass_by_ref temp)
{
temp.n=temp.n*2;
temp.n2=temp.n2*2;
}
}
class apply7
{
public static void main(String args[])
{
int x=5,y=10;
pass_by_refobj=new pass_by_ref();
obj.get(x,y); //Pass by Value munotes.in
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73 System.out.println("Initial Values are -- ");
System.out.println(+obj.n);
System.out.println(+obj.n2);
obj.doubleit(obj); //Pass by Reference
System.out.println("Final Values are");
System.out.println(+obj.n);
System.out.println(+obj.n2);
}
}
4.2.7 Abstract Classes
Definition: An abstract class is a class that is declared as abstract. It may
or may not include abstract methods. Abstract classes cannot be
instantiated, but they can be subclass. An abstract method is a method that
is declared without an implementation (without braces, and followed by a
semicolon), like this:
abstract void studtest (introllno, double test fees);
If a class includes abstract methods, the class itself must be declared
abstract, as in:
public abstract class Graphic Object
{
// declare fields
// declare non -abstract methods
abstract void draw();
}
When an abstract class is subclass, the subclass usually provides
implementations for all of the abstract methods in its parent class.
However, if it does not, the subclass must also be declared abstract.
For example: In an object -oriented drawing application, you can draw
circles, rectangles, lines, Bezier curves, and many other graphic objects.
These objects all have certain states (for example: position, orientation,
line color, fill color) and behaviors (for example: move To, rot ate, resize,
draw) in common. Some of these states and behaviors are the same for all
graphic objects —for example: position, fill color, and move To. Others
require different implementations —for example, resize or draw. All
Graphic Objects must know how to draw or resize themselves; they just
differ in how they do it. This is a perfect situation for an abstract super
class. You can take advantage of the similarities and declare all the
graphic objects to inherit from the same abstract parent object —for
exam ple, Graphic Object, as shown in the following figure. munotes.in
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74
How to implement above diagram concept with source code:
abstract class Graphic Object
{
int x, y;
...
Voidmove To (intnew X, intnew Y)
{
...
}
abstract void draw();
abstract void resize();
}
Each non -abstract subclass of Graphic Object, such as Circle and
Rectangle, must provide implementations for the draw and resize
methods:
class Circle extends Graphic Object {
void draw() {
...
}
void resize( ) {
...
}
}
class Rectangle extends Graphic Object {
void draw() {
...
}
void resize() {
...
}
}
Abstract classes are those which can be used for creation of
objects. However their methods and constructors can be used by the child
or extended class. The n eed for abstract classes is that you can generalize
the super class from which child classes can share its methods. The
subclass of an abstract class which can create an object is called as
"concrete class". munotes.in
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75 For example:
abstract class A
{
abstract void method1();
void method2()
{
System.out.println("this is real method");
}
}
class B extends A
{
void method1()
{
System.out.println("B is execution of method1");
}
}
class demo
{
public static void main(String arg[])
{
B b=new B();
b.method1() ;
b.method2();
}
}
4.2.8 Extending the class:
Inheritance allows to subclass or child class to access all methods and
variables of parent class.
Syntax:
Class subclass name extends super class name
{
Varables;
Methods;
…..
}
For example: calculate area an d volume by using In hertance.
class data
{
int l;
int b; munotes.in
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76 data(int c, int d)
{
l=c;
b=d;
}
int area( )
{
return(l*b);
}
}
class data2 extends data
{
int h;
data2(intc,int d, int a)
{
super(c,d);
h=a;
}
int volume()
{
return(l*b*h);
}
}
class DataDemo
{
public static void main(String args[])
{
data2 d1=new data2(10,20,30);
int area1=d1.area(); //superclass method
int volume1=d1.volume( );// subclass method
System.out.println("Area="+area1);
System.out.println("Volume="+volume1);
}
}
Output:
C:\cc>javac da taDemo.java
C:\cc>java dataDemo
Area=200
Volume=6000
"Is A" - is a subclass of a super class (ex: extends)
"Has A" - has a reference to (ex: variable, ref to object). munotes.in
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77 o Access Control –
Away to limit the access others have to your code.
Same package - can access each others’ variables and
methods, except for private members.
Outside package - can access public classes. Next, can
access members that are public. Also, can access protected
members if the class is a subclass of that class.
Same package - use package keyword in first line of source file, or
no package keyword and in same directory.
o Keywords -
1. public - outside of package access.
2. [no keyword] - same package access only.
3. protected - same package access. Access if clas s is a
subclass of, even if in another package.
4. private - same class access only.
4.3 SUMMARY:
In this unit, we learn the concept of class and how to create method
and how to pass parameters by value and by reference and method
overloading with example. In this unit, we also learn the concept of
inheritance.
4.4 LIST OF REFERENCES
1. Java 2: The C omplete Reference, Fifth Edition, Herbert Schildt, Tata
McGraw Hill.
2. An Introduction to Object oriented Programming with JAVA, C
THOMAS WU
3. www.javatpoint.com
4.5. QUESTION
1. Explain class in detail with suitable example.
2. Explain Methods with a Return Type with suitable example.
3. What is method overloading explain with suitable example.
4. Write a short note on abstract class.
munotes.in
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785
CONSTRUCTORS
Unit Structure
5.1. Introduction
5.1.1. Rules for creating constructor
5.1.2. Default Constructor
5.1.3. Java Parameterized Constructor
5.1.4. Constructor Overloading
5.1.5. Copy Constructor
5.1.6. Super Keyword
5.1.7. Static keyword
5.1.8. Understanding the problem without static variable
5.1.9. Java static method
5.2. Garbage Collection
5.2.1. Two types of garbage collection
5.3. Summary
5.4 List of References
5.5 Questions
5.1. INTRODUCTION
In Java, a constructor is a block of codes similar to the method. It
is called when an instance of the class is created. At the time of calling
constructor, memory for the object is allocated in the memory.
It is a special type of method which is used to initialize the object.
Every time an o bject is created using the new() keyword, at least
one constructor is called.
It calls a default constructor if there is no constructor available in
the class. In such case, Java compiler provides a default constructor by
default.
There are two types of co nstructors in Java:
1) Default constructor
2) Parameterized constructor.
Note: It is called constructor because it constructs the values at the time of
object creation. It is not necessary to write a constructor for a class. It is
because java compiler creates a default constructor if your class doesn't
have any.munotes.in
Page 79
795.1.1. Rules for cr eating constructor
There are two rules defined for the constructor.
1.Constructor name must be the same as its class name
2.A Constructor must have no explicit return type
3.A Java constructor cannot be abstract, static, final, and
synchronized
5.1.2. Default C onstructor
A constructor is called "Default Constructor" when it doesn't have any
parameter.
Syntax of default constructor:
(){}
Example of default constructor
1.Java Default Constructor
//Java Program tocreate andcalladefault constructo r
class Bike1{
//creating adefault constructor
Bike1(){System.out.println("Bike iscreated");}
//main method
public static void main(String args[]){
//calling adefault constructor
Bike1 b=new Bike1();
}
}
Output:
Bike is created
2.Example of default constructor that displays the default values
//Let us see another example of default constructor
//which displays the default values
class Student3{
int id;
String name;
//method to display the value of id and name
void displ ay(){System.out.println(id+" "+name);}
public static void main(String args[]){
//creating objects
Student3 s1=new Student3();
Student3 s2=new Student3();
//displaying values of the objectmunotes.in
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80s1.display();
s2.display();
}
}
Output:
0n u l l
0n u l l
In the above class, you are not creating any constructor so compiler
provides you a default constructor. Here 0 and null values are provided by
default constructor.
5.1.3. Java Parameterized Constructor
A constructor which has a specific number of parameters is called
a parameterized constructor. The parameterized constructor is used to
provide different values to distinct objects. However, you can provide the
same values also.
Example of parameterized constructor
In this example, we have created t he constructor of Student class that have
two parameters. We can have any number of parameters in the
constructor.
//Java Program to demonstrate the use of the parameterized constructor.
class Student4{
int id;
String name;
//creating a par ameterized constructor
Student4(inti,String n){
id = i;
name = n;
}
//method to display the values
void display(){System.out.println(id+" "+name);}
public static void main(String args[]){
//creating objects and passing values
Student4 s1 = new Student4(111,"Karan");
Student4 s2 = new Student4(222,"Aryan");
//calling method to display the values of object
s1.display();
s2.display();munotes.in
Page 81
81}
}
Output:
111 Karan
222 Aryan
5.1.4. Constructor Overloading in Java
In Java, a constructor is just like a method but without return type.
It can also be overloaded like Java methods.
Constructor overloading in Java is a technique of having more than
one constructor with different parameter lists. They are arranged in aw a y
that each constructor performs a different task. They are differentiated by
the compiler by the number of parameters in the list and their types.
Example of Constructor Overloading
//Java program to overload constructors
class Student5{
int id;
String name;
int age;
//creating two arg constructor
Student5(inti,String n){
id = i;
name = n;
}
//creating three arg constructor
Student5(inti, Stringn, int a){
id = i;
name = n;
age=a;
}
void display(){System.out.println(id+" "+name+" "+age);}
public static void main(String args[]){
Student5 s1 = new Student5(111,"Karan");
Student5 s2 = new Student5(222,"Aryan",25);
s1.display();
s2.display();
}
}munotes.in
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82Output:
111 K aran 0
222 Aryan 25
5.1.5. Copy Constructor
There is no copy constructor in Java. However, we can copy the values
from one object to another like copy constructor in C++.
There are many ways to copy the values of one object into another in
Java. They are:
By constructor
By assigning the values of one object into another
By clone() method of Object class
In this example, we are going to copy the values of one object into
another using Java constructor.
//Java program to initialize the values from one object to another object.
class Student6{
int id;
String name;
//constructor to initialize integer and string
Student6(inti,String n){
id = i;
name = n;
}
//constructor to initialize another object
Student6(Student6 s){
id = s.id;
name =s.name;
}
void display(){System.out.println(id+" "+name);}
public static void main(String args[]){
Student6 s1 = new Student6(111,"Karan");
Student6 s2 = new Student6(s1);
s1.display();
s2.display();
}
}
Output:
111 Karan
111 Karanmunotes.in
Page 83
835.1.6. Super Keyword
The super keyword in Java is a reference variable which is used to
refer immediate parent class object.
Whenever you create the instance of subclass, an instance of parent
class is created implicitly which is referred by super reference variable.
Usage of Java super Keyword
1.super can be used to refer immediate parent class instance variable.
2.super can be used to invoke immediate parent class method.
3.super() can be used to invoke immediate parent class constructor.
super is used to refer immediate parent class instance variable.
We can use super keyword to access the data member or field of
parent class. It is used if parent class and child class have same fields.
class Animal{
String color="white";
}
class Dog extends Animal{
String color="black";
voidprintColor(){
System.out.println(color);//prints color of Dog class
System.out.println(super.color);//prints color of Animal class
}
}
class TestSuper1{
public static void main(String args[]){
Dog d=new Dog();
d.printColor();
}}
Output:
black
white
In the above example, Animal and Dog both classes have a
common property color. If we print color property, it will print the color of
current class by default. To access the parent property, we need to use
super keyword.
5.1.7.static keyword
The static keyword in Java is used for memory management
mainly. We can apply static keyword with variables, methods, blocks and
nested classes. The static keyword belongs to the class than an instance of
the class.munotes.in
Page 84
84The static can be:
1.Variable (also known as a class variable)
2.Method (also known as a class method)
3.Block
4.Nested class
1) Java static variable
If you declare any variable as static, it is known as a static variable.
The static variable can be used to refer to the common property of
all objects (which is not unique for each object), for example, the
company name of employees, college name of students, etc.
The static variable gets memory only once in the class area at the
time of class loading.
Advantages of static variable
It makes your program memory efficient (i.e., it saves memory).
6.1.8. Understanding the problem without static variable
class Student{
introllno;
String name;
String college="ITS";
}
Suppose there are 500 students in my college, now all instance data
members will get memory each time when the object is created. All
students have its unique rollno and name, so instance data member is good
in such case. Here, "c ollege" refers to the common property of all objects.
If we make it static, this field will get the memory only once.
1)Example of static variable
//Java Program to demonstrate the use of static variable
class Student{
introllno;//instance variable
String name;
static String college ="ITS";//static variable
//constructor
Student(int r, String n){
rollno = r;
name = n;
}
//method to display the valuesmunotes.in
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85void display (){System.out.println(rollno+" "+name+" "+college);}
}
//Test class to show the values of objects
public class TestStaticVariable1{
public static void main(String args[]){
Student s1 = new Student(111,"Karan");
Student s2 = new Student(222,"Aryan");
//we can change the college of all objects by the single line of code
//Student.college="BBDIT";
s1.display();
s2.display();
}
}
Output:
111 Karan ITS
222 Aryan ITS
2)Program of counter by static variable
As we have mentioned above, static variable will get the memory
only once, if any object changes the value of the static variable, it will
retain its value.
//Java Program to illustrate the use of static variable which
//is shared with all objects.
class Counter2{
staticint count=0;//will get memory only once and retain its value
Counter2(){
count++;//incrementing the value of static variable
System.out.println(count);
}
public static void main(String args[]){
//creating objects
Counter2 c1=new Counter2();
Counter2 c2=new Counter2();
Counter2 c3=new Counter2();
}
}munotes.in
Page 86
86Output:
1
2
3
5.1.9. Java static method
If you apply static keyword with any method, it is known as static method.
A static method belongs to the class rather than the object of a
class.
A static method can be invoked without the need for creating an
instance of a class.
A static method can access static data member and can change the
value of it.
Example of static method
//Java Program to demonstrate the use of a static method.
class Student{
introllno;
String name;
static St ring college = "ITS";
//static method to change the value of static variable
static void change(){
college = "BBDIT";
}
//constructor to initialize the variable
Student(int r, String n){
rollno = r;
name = n;
}
//method to display values
void display(){System.out.println(rollno+" "+name+" "+college);}
}
//Test class to create and display the values of object
public class TestStaticMethod{
public static void main(String args[]){
Student.change();/ /calling change method
//creating objects
Student s1 = new Student(111,"Karan");munotes.in
Page 87
87Student s2 = new Student(222,"Aryan");
Student s3 = new Student(333,"Sonoo");
//calling display method
s1.display();
s2.display();
s3.displ ay();
}
}
Output:
111 Karan BBDIT
222 Aryan BBDIT
333 Sonoo BBDIT
5.2. GARBAGE COLLECTION
Java applications obtain objects in memory as needed. It is the task
of garbage collection (GC) in the Java virtual machine (JVM) to
automatically determine what memory is no longer being used by a Java
application and to recycle this memory for other uses. Because memory is
automatically reclaimed in the JVM ,Java application developers are not
burdened with having to explicitly free memory objects that are not being
used. The GC operation is based on the premise that most objects used in
the Java code are short -lived and can be reclaimed shortly after their
creation. Because unreferenced obj ects are automatically removed from
the heap memory, GC makes Java memory -efficient.
Garbage collection frees the programmer from manually dealing
with memory deallocation. As a result, certain categories of application
program bugs are eliminated or subs tantially reduced by GC:
Dangling pointer bugs, which occur when a piece of memory is freed
while there are still pointers to it, and one of those pointers is
dereferenced. By then the memory may have been reassigned to
another use with unpredictable resul ts.
Double free bugs, which occur when the program tries to free a
region of memory that has already been freed and perhaps already
been allocated again.
Certain kinds of memory leaks, in which a program fails to free
memory occupied by objects that have b ecome unreachable, which
can lead to memory exhaustion.munotes.in
Page 88
885.2.1. Two types of garbage collection
A minor or incremental garbage collection is said to have
occurred when unreachable objects in the young generation heap
memory are removed.
Am a j o ro r full garbage collection is said to have occurred when
the objects that survived the minor garbage collection and copied
into the old generation or permanent generation heap memory are
removed. When compared to young generation, garbage collection
happens l ess frequently in old generation.
To free up memory, the JVM must stop the application from
running for at least a short time and execute GC. This process is called
“stop-the-world .” This means all the threads, except for the GC threads,
will stop executi ng until the GC threads are executed and objects are freed
up by the garbage collector.
Modern GC implementations try to minimize blocking “stop -the-
world” stalls by doing as much work as possible on the background (i.e.
using a separate thread), for exam ple marking unreachable garbage
instances while the application process continues to run.
Garbage collection consumes CPU resources for deciding which memory
to free. Various garbage collectors have been developed over time to
reduce the application pause s that occur during garbage collection and at
the same time to improve on the performance hit associated with garbage
collection.
The traditional Oracle HotSpot JVM has four ways of performing the
GC activity:
Serial where just one thread executed the GC
Parallel where multiple minor threads are executed simultaneously
each executing a part of GC
Concurrent Mark Sweep (CMS), which is similar to parallel, also
allows the execution of some application threads and reduces the
frequency of stop -the-world GC
G1which is also run in parallel and concurrently but functions
differently than CMS
Many JVMs, such as Oracle HotSpot, JRockit, OpenJDK, IBM J9,
and SAP JVM, use stop -the-world GC techniques. Modern JVMs like
Azul Zing use Continuously Concurrent Compactin g Collector (C4) ,
which eliminates the stop -the-world GC pauses that limit scalability in the
case of conventional JVMs.munotes.in
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895.3. SUMMARY
In this chapter we study about constructor, Rules for creating
constructor, Default Constructor, Constructor Overloading, Copy
Constructor.
Also we study about Super Keyword, static keyword, static
method, Last point of this chapter is Garbage Collection and types of
Garbage Collection
5.4 LIST OF REFERENCES
1. Java 2: The Complete Reference, Fifth Edition, He rbert Schildt, Tata
McGraw Hill.
2. An Introduction to Object oriented Programming with JAVA, C
THOMAS WU
3. www.javatpoint.com
5.5 QUESTIONS
1. Write a short note on constructor.
2. Explain default contractors with suitable Example.
3. Explain Parameterized constructor with suitable example.
4. Explain static keyword.
5. write a short note on garbage collection
munotes.in
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90Unit III
6
INHERITANCE
Unit Structure
6.0 Objective
6.1. Introduction
6.1.1. Why use inheritance in java
6.1.2. Terms used in Inheritance
6.1.3. Types of inheritance in java
6.2. Types of inheritance in java
6.2.1. Single Inheritance
6.3. Multilevel Inheritance
6.4. Hierarchical Inheritance
6.5. Multiple inheritance is not supported in java
6.6. Abstract class in Java
6.6.1. Ways to achieve Abstraction
6.7. Abstract class having constructor, data member and methods
6.8. Interface in Java
6.9. The relationship between classes and interfaces
6.10. Multiple inheritance in Java by interface
6.11. Interface inheritance
6.12. Default Method in Interface
6.13. Static Method in Interface
6.14. Difference between abstract class and interface
6.15. Summary
6.16 Questions
6.17 References
6.0 OBJECTIVE
To understand the concept of Inheritance, Types of Inheritance,
Abstract class, Difference between abstract class and interface, etc…
6.1.INTRODUCTION INHERITANCE
Inheritance in Java is amechanism in which one object acquires all the
properties and behaviors of a parent object. It is an important part
ofOOPs (Object Oriented programming system).munotes.in
Page 91
91The idea behind inheritance in Java is that you can create
newclasses that are built upon existing classes. When you inherit from an
existing class, you can reuse methods and fields of the parent class.
Moreover, you can add new methods and fields in your current class also.
Inheritance represents the IS-A relationship which is also known
as aparent -child relationship.
6.1.1. Why use inheritance in java
oForMethod Overriding (soruntime polymorphism can be
achieved).
oFor Code Reusability.
6.1.2. Terms used in Inheritance
oClass: A class is a group of objects which have common
properties. It is a template or blueprint from which objects are
created.
oSub Class/Child Class: Subclass is a class which inherits the
other class. It is also called a derived class, extended class, or child
class.
oSuper Class/Parent Class: Superclass is the class from where a
subclass inherits the features. It is also called a base class or a
parent class.
oReusability: As the name specifies, reusability is a mechanism
which facilitates you to reuse the fields and methods of the existing
class when you create a new class. You can use the same fields and
methods already defined in the previous class.
6.1.3.The syntax of Java Inheritance
class Subclass -name extends Superclass -name
{
//methods andfields
}
Theextends keyword indicates that you are making a new class that
derives from an existing class. The meaning of "extends" is to increase the
functionality.
In the terminology of Java, a class which is inherited is called a parent or
superclass, and the new class is called child or subclass.munotes.in
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92Java Inheritance Example
As displayed in the above figure, Programmer is the subclass and
Employee is the superclass. The relationship between the two classes
isProgrammer IS -A Employee . It means that Programmer is a type of
Employee.
class Employee{
float salary= 40000 ;
}
class Programmer extends Employee{
intbonus= 10000 ;
public static void main(String args[]){
Programmer p=newProgrammer();
System.out.println( "Programmer salary is:"+p.salary);
System.out.println( "Bonus ofProgrammer is:"+p.bonus);
}
}
Output:
Programmer salary is:40000.0
Bonus of programmer is:10000
In the above example, Programmer object can access the field of own
class as well as of Employee class i.e. code reusability.munotes.in
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936.2. TYPES OF INHERITANCE IN JAVA
On the basis of class, there can be three types of inheritance in
java: single, multilevel and hierarchical.
In java programming, multiple and hybrid inheritance is supported
through interface only. We will learn about interfaces later.
When one class inherits multiple classes, it is known as multiple
inheritance. For Example:
6.2.1. Single Inheritance Example
When a class inherits another class, it is known as a single
inheritance . In the example given below, Dog class inherits the Animal
class, so there is the single inheritance.
File: TestInheritance.java
class Animal{
void eat(){System.out.println( "eating..." );}
}
class Dog extends Animal{
void bark(){System.out.println( "barking..." );}munotes.in
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94}
class TestInheritance{
public static void main(String args[]){
Dog d=newDog();
d.bark();
d.eat();
}}
Output:
barking...
eating...
6.3. MULTILEVEL INHERITANCE EXAMPLE
When there is a chain of inheritance, it is known as multilevel
inheritance . As you can see in the example given below, BabyDog class
inherits the Dog class which again inherits the Animal class, so there is a
multilevel inheritance.
File: TestInheritance2.java
class Animal{
void eat(){System.out.println( "eating..." );}
}
class Dog extends Animal{
void bark(){ System.out.println( "barking..." );}
}
class BabyDog extends Dog{
void weep(){System.out.println( "weeping..." );}
}
class TestInheritance2{
public static void main(String args[]){
BabyDog d=newBabyDog();
d.weep();
d.bark();
d.eat();
}}
Output:
weeping...
barking...
eating...munotes.in
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956.4. HIERARCHICAL INHERITANCE
When two or more classes inherits a single class, it is known
ashierarchical inheritance . In the example given below, Dog and Cat
classes inherits the Animal class, so there is hierarchical inheritance.
File: TestInheritance3.java
class Animal{
void eat(){System.out.println( "eating..." );}
}
class Dog extends Animal{
void bark(){System.out.println( "barking..." );}
}
class Catextends Animal{
void meow(){System.out.println( "meowing..." );}
}
class TestInheritance3{
public static void main(String args[]){
Catc=newCat();
c.meow();
c.eat();
//c.bark();//C.T.Error
}}
Output:
meowing...
eating...
6.5. MULTIPLE INHERITANCE IS NOT SUPPORTED
IN JAVA
To reduce the complexity and simplify the language, multiple
inheritance is not supported in java.
Consider a scenario where A, B, and C are three classes. The C class
inherits A and B classes. If A and B classes have the same method an dy o u
call it from child class object, there will be ambiguity to call the method of
A or B class.
Since compile -time errors are better than runtime errors, Java renders
compile -time error if you inherit 2 classes. So whether you have same
method or different, there will be compile time error.
class A{
void msg(){System.out.println( "Hello" );}munotes.in
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96}
class B{
void msg(){System.out.println( "Welcome" );}
}
class Cextends A,B{ //suppose ifitwere
public static void main(String args[]){
Cobj=newC();
obj.msg(); //Now which msg() method would beinvoked?
}
}
Output:
Compile Time Error
6.6. ABSTRACT CLASS IN JAVA
A class which is declared with the abstract keyword is known as an
abstract class in Java.I tc a nh a v ea b s t r a c ta n dn o n -abstract methods
(method with the body).
Before learning the Java abstract class, let's understand the
abstraction in Java first.
Abstraction is a process of hiding t he implementation details and showing
only functionality to the user.
Another way, it shows only essential things to the user and hides
the internal details, for example, sending SMS where you type the text and
send the message. You don't know the interna lp r o c e s s i n ga b o u tt h e
message delivery.
Abstraction lets you focus on what the object does instead of how
it does it.
6.6.1. Ways to achieve Abstraction
There are two ways to achieve abstraction in java
1.Abstract class (0 to 100%)
2.Interface (100%)
Aclass which is declared as abstract is known as an abstract
class. It can have abstract and non -abstract methods. It needs to be
extended and its method implemented. It cannot be instantiated.
oAn abstract class must be declared with an abstract keyword.
oItcan have abstract and non -abstract methods.
oIt cannot be instantiated.
oIt can have constructors and static methods also.munotes.in
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97oIt can have final methods which will force the subclass not to
change the body of the method.
Example of abstract class
abstract classA{}
A method which is declared as abstract and does not have
implementation is known as an abstract method.
Example of abstract method
abstract void printStatus(); //nomethod body andabstract
Example of Abstract class that has an abstract method
In this example, Bike is an abstract class that contains only one
abstract method run. Its implementation is provided by the Honda class.
abstract class Bike{
abstract void run();
}
class Honda4 extends Bike{
void run(){System.out.println( "runnin gsafely" );}
public static void main(String args[]){
Bike obj=newHonda4();
obj.run();
}
}
Output:
running safely
example of Abstract class in java
File: TestBank.java
abstract class Bank{
abstract intgetRateOfInterest();
}
class SBIextends Bank{
intgetRateOfInterest(){ return 7;}
}
class PNB extends Bank{
intgetRateOfInterest(){ return 8;}
}
class TestBank{
public static void main(String args[]){
Bank b;
b=newSBI();munotes.in
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98System.out.println( "Rate ofInterest is:"+b.getRateOfInterest()+ "%");
b=newPNB();
System.out.println( "Rate ofInterest is:"+b.getRateOfInterest()+ "%");
}}
Output:
Rate of Interest is: 7 %
Rate of Interest is: 8 %
6.7. ABSTRACT CLASS HAV ING CONSTRUCTOR,
DATA MEMBER AND METHODS
An abstract class can have a data member, abstract method,
method body (non -abstract method), constructor, and even main() method.
File: TestAbstraction2.java
//Example ofanabstract class thathasabstract andnon-abstract methods
abstract class Bike{
Bike(){System.out.println( "bike iscreated" );}
abstract void run();
void changeGear(){System.out.println( "gear changed" );}
}
//Creating aChild class which inherits Abstract class
class Honda extends Bike{
void run(){System.out.println( "running safely.." );}
}
//Creating aTest class which calls abstract andnon-abstract methods
class TestAbstraction2{
public static void main (String args[]){
Bike obj=newHonda();
obj.run();
obj.changeGear();
}
}
Output:
bike is created
running safely..
gear changed
6.8. INTERFACE IN JAVA
Aninterface in Java is a blueprint of a class. It has static
constants and abstract methods.munotes.in
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99The interface in Java is a mechanism to achieve abstraction .T h e r e
can be only abstract methods in the Java interface, not method body. It is
used to achieve abstraction and multiple inheritance in Java.
In other words, you can say that interfaces can have abstract
methods and variables. It cannot have a method body.
Java Interface also represents the IS -A relationship .
It cannot be instantiated just like the abstract class.
we can have default and static methods in an interface.
we can have private methods in an interface.
Why use Java interface?
There are mainly three reasons to use interface. They are given below.
oIt is used to achieve abstraction.
oBy interface, we can support the functionality of multiple
inheritance.
oIt can be used to achieve loose coupling.
How to declare an interface?
An interface is declared by using the interface keyword. It provides
total abstraction; means all the methods in an interface are declared with
the empty body, and all the fields are public, static and final by default. A
class that implements an interface must implement all the methods
declared in the interface.
Syntax:
interface {
//declare constant fields
//declare methods thatabstract
//bydefault.
}
6.9. THE RELATIONSHIP BETWEEN CLASSES AND
INTERFACES
As shown in the figure given below, a class extends another class,
an interface extends another interface, but a class implements an
interfa ce.
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100Java Interface Example
In this example, the Printable interface has only one method, and its
implementation is provided in the A6 class.
interface printable{
void print();
}
class A6implements printable{
public void print(){System.out.println( "Hello" );}
public static void main(String args[]){
A6obj=newA6();
obj.print();
}
}
Output:
Hello
Java Interface Example: Bank
Let's see another example of java interface which provides the
implementation of Bank interface.
File: TestInterface2.java
interface Bank{
float rateOfInterest();
}
class SBIimplements Bank{
public float rateOfInterest(){ return 9.15f;}
}
class PNB implements Bank{
public float rateOfInterest(){ return 9.7f;}
}
class TestInterface2{
public static void main(String[] args){
Bank b=newSBI();
System.out.println( "ROI: "+b.rateOfInterest());
}}
Output:
ROI: 9.15munotes.in
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1016.10MULTIPLE INHERITANCE IN JAVA BY
INTERFACE
If a class implements multiple interfaces, or an interface extends multiple
interfaces, it is known as multiple inheritance.
interface Printable{
void print();
}
interface Showable{
void show();
}
class A7implements Printable,Showable{
public void print(){System.out.println( "Hello" );}
public void show(){System.out.println( "Welcome" );}
public static void main(String args[]){
A7obj=newA7();
obj.print();
obj.show();
}
}
Output:
Hello
Welcome
6.11. INTERFACE INHERITANCE
A class implements an interface, but one interface extends another
interface.
interface Printable{
void print();
}munotes.in
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102interface Showable extends Printable{
void show();
}
class TestInterface4 implements Showable{
public void print(){System.out.println( "Hello" );}
public void show(){System.out.println( "Welcome" );}
public static void main(String args[]){
TestInterface4 obj=newTestInterface4();
obj.print();
obj.show();
}
}
Output:
Hello
Welcome
6.12. DEFAULT METHOD IN INTERFACE
We can have method body in interface. But we need to make it
default method. Let's see an example:
File: TestInterfaceDefault.java
interface Drawable{
void draw();
default void msg(){System.out.println( "default method" );}
}
class Rectangle implements Drawable{
public void draw(){System.out.println( "drawing rectangle" );}
}
class TestInterfaceDefault{
public static void main(String args[]){
Drawable d=newRectangle();
d.draw();
d.msg();
}}
Output:
drawing rectangle
default methodmunotes.in
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1036.13. STATIC METHOD IN INTERFACE
We can have static method in interface. Let's see an example:
File: TestInterfaceStatic.java
interface Drawable{
void draw();
static intcube( intx){return x*x*x;}
}
class Rectangle implements Drawable{
public void draw(){System.out.println( "drawing rectangle" );}
}
class TestInterfaceStatic{
public static void main(String args[]){
Drawable d=newRectangle();
d.draw();
System.out.println(Drawable.cube( 3));
}}
Output:
drawing rectangle
27
6.14.DIFFERENCE BETWEEN ABSTRACT CLASS AND
INTERFACE
Abstract class and interface both are used to achieve abstraction
where we can declare the abstract methods. Abstract class and interface
both can't be instantiated.
But there are many differences between abstract class and interface
that are given below.
Abstract class Interface
1) Abstract class can have abstract
and non -abstract methods.Interface can have only
abstract methods. Since Java 8, it
can have default and static
methods also.
2) Abstract class doesn't support
multiple inheritance .Interface supports multiple
inheritance .
3) Abstract class can have final,
non-final, static and non -static
variables .Interface has only static and final
variables .munotes.in
Page 104
1044) Abstract class can provide the
implementation of interface .Interface can't provide the
implementation of abstract class .
5) The abstract keyword is used to
declare abstract class.Theinterface keyword is used to
declare interface.
6) An abstract class can extend
another Java class and implement
multiple Java interfaces.Aninterface can extend another
Java interface only.
7) An abstract class can be
extended using keyword "extends".Aninterface can be implemented
using keyword "implements".
8) A Java abstract class can have
class members like private,
protected, etc.Members of a Java interface are
public by default.
9)Example:
public abstract class Shape{
public abstract void draw();
}Example:
public interface Drawable {
void draw();
}
Simply, abstract class achieves partial abstraction (0 to 100%) whereas
interface achieves fully abstraction (100%).
6.15. SUMMARY:
In this chapter we discuss the detailed concept of Inheritance, types
of inheritance, Super keyword, Abstract classes, how to use interfaces,
Static Method in Interface ,Static Method in Interface ,Difference between
abstract class and interface ,etc..
6.16. QUESTIONS:
1)Explain the term used in Inheritance.
2)What are the types of Inheritance?
3)Explain multiple inheritances with satiable example.
4)Why mu ltiple inheritances is not supported in java.
5)Write a short note on abstract class.
6)Write a Difference between abstract class and interface .
6.17 REFERENCE:
1) Java ™: The Complete Reference, Seventh Edition
2)www.javatpoint.com
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1057
PACKAGES
Unit Structure
7.0Objective
7.1 Introduction
7.2Creating Packages
7.3Default Packages
7.4Importing Packages
7.5Using A Package
7.6Summary
7.7List of References
7.8 Bibliography
7.9 Model Questions
7.0 OBJECTIVE
In this chapter, you will be going to learn:
Concept of package
Built -In packages available
Creating and using user defined packages
7.1 INTRODUCTION
Package in java is a mechanism to encapsulate a group of classes,
sub packages and interfaces. Package in java can be categorized in two
forms, built-in package and user defined package. Packages are used for:
Preventing naming conflicts.
Making searching, usage of classes, interfaces, enumerations and
annotations easier.
Package provides access protection.
7.2 CREATING PACKAGES
The package k eyword is used to create a package in java. We can
add multiple classes and interfaces to a created package by using package
name at the top of the program and saving it in package directory.munotes.in
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106Example:
1)//SAVE AS Addition.java
package mypack;
public class Addition
{
public void add(double a,double b)
{
System.out.println("Addition :" + (a+b));
}
}
Compiling Java Package:
Syntax: javac -d directory javafilename
javac -d . Addition.java
Here, -d specifies the destination where to put the generated class file. To
keep the package in the same directory , use .(dot).
2) // save as Factorial.java
package mypack;
import java.util.*;
public class Factorial
{
int i,fact=1;
public void fact(int number)
{
for(i=1;i<=number;i++)
{
fact=fact*i;
}
System.out.println("Factorial of "+number+" is: "+fact);
}
}
Compiling Java Package:
javac -d .Factorial.javamunotes.in
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1077.3DEFAULT PACKAGES
Package Description
java.ioProvides system input and output through data stream,
serialization and the file system. Example, Input Stream,
Output Stream, Print Writer, Writer etc.
java.langProvides classes that are fundamental to the design of the
java programming language. Example, Object, System,
Runnable etc.
java.sqlProvides the API for accessing and processing data stored
in a data source. Example, Statement, ResultSet, Drier
Manager etc.
java.time The main API for Dates, times, instances and durations.
java.util Contains collection Framework.
java.applet Contains classe s for creating applet
java.awtContains the classes for implementing the components for
graphical user interface.
java.netContains the classes for supporting networking
operations.
7.4IMPORTING PACKAGES
There are two ways to access the package from outside the package.
1) Using packagename.*
Syntax: import packagename.*
Using this syntax, all the classes and interfaces of this package will
be accessible but not subpackage.
Example: import mypack.*;
2) Using packagename.classname
Syntax import packagename.classname
If you import package.classname then only declared class of this
package will be accessible.
Example: import mypack.Factorial;
import mypack.addition;munotes.in
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1087.5USING A PACKAGE
Example:
import java.util.Scanner;
import mypack.Factorial;
import mypack.Addition;
class TestPackage
{
public static void main(String arg[])
{
Factorial f=new Factorial();
System.out.println("enter number to find out factorial ");
Scanner sc=new Scanner(System.in);
int n=sc.nextInt ();
f.fact(n);
System.out.println("Enter 2 numbers: ");
Addition a=new Addition();
double p=sc.nextDouble();
double q=sc.nextDouble();
a.add(p,q);
}
}
Output:
enter number to find out factorial
5
Factorial of 5 is: 120
Enter 2 numbers:
5
6
Addition :11.0munotes.in
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1097.6SUMMARY
In this chapter, we learn concept of package, built in collection of
packages available in java language, creating and accessing user defined
packages.
7.7LIST OF REFERENCES
Java, A Beginner’s Guide, Eighth Edition, Herbert Schildt, McGraw Hill
Publisher
Java: The Complete Reference, Eleventh Edition, Herbert Schildt,
McGraw Hill Publisher
7.8BIBLIOGRAPHY
https://www.javatpoint.com/java -tutorial
https://www.geeksforgeeks.org/java
https://www.beginnersbook.com/java -tutorial -for-beginners -with-
examples/
http://www.programiz.com/java -programming/
https://docs.oracle.com/javase/tutorial/
7.9 MODEL QUESTIONS
1.Which of these keywords is used t o define packages in Java?
a) pkg
b) Pkg
c) package
d) Package
2.Which of these is a mechanism for naming and visibility control of a
class and its content?
a) Object
b) Packages
c) Interfaces
d) None of the Mentioned.
3.Which of these access specifiers can be used for a class so that its
members can be accessed by a different class in the different package?
a) Public
b) Protected
c) Private
d) No Modifiermunotes.in
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1104.Which of the following is the correct way of importing an entire
package ‘pkg’?
a) import p ackage.;
b) Import package;
c) import package.*;
d) Import package.*;
5.What is the maximum number of Java Class files that can be kept inside
a single Java Package?
a)8
b)64
c)128
d)Unlimited
6.When importing a package, the Class is actually importing ____.
a)Classes or Interfaces from the package
b)Constants
c)Methods
d)None of the above
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111Unit IV
8
ENUMERATIONS, ARRAYS
Unit Structure :
8.0 Introduction
8.1 Objectives
8.2 Java Array
8.2.0 Advantages
8.2.1 Disadvantages
8.3 Types of Array in java
8.3.0 Single Dimensional Array in Java
8.3.1 Multidimensional Array in Java
8.4 Java -The Vec tor Class
8.5 Sample Questions
8.0 INTRODUCTION
An array is a data structure supported by all the programming
languages that stores multiple values of the same type in a fixed length
structure. Vector implements a dynamic array. It is similar to Array L ist.
In this chapter we will cover about Enumerations, Arrays . We
will discuss about Vector. Then we will cover Operations with Array and
Vector supported in Java. At the end we will discuss program of array and
vector in Java language.
8.1 OBJECTIVES
After going through this unit, you should be able to:
Know theory behind Array and Vector
Write Array Program with its different Types
Write Vector Program with its different Methods
8.2 JAVA ARRAY
An array isacollection ofsimilar type ofelements thathave a
contiguous memory location.
Java array is an object which contains elements of a similar data
type.munotes.in
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112It is a data structure where we store similar elements.
We can store only a fixed set of elements in a Java array.
Array in java isindex -based, thefirst element of thearray isstored
at the 0index.
8.2.0Advantages
Code Optimization: Itmakes thecode optimized, wecanretrieve or
sortthedata Efficiently.
Random access: Wecangetanydata located atanindex position.
8.2.1Disadvantages
SizeLimit: Wecan store only thefixed sizeof elements inthearray.
Itdoesn't grow its size at runtime. To solve this problem, collection
framework is used in Java which grows automatically.
8.3 TYPES OF ARRAY IN JAVA
There aretwo ty pesof array.
Single Dimensional Array
Multidimensional Array
8.3.0 Single Dimensional Array in Java
Syntax to Declare an Array in Java
1.dataType[] arr;
2.dataType []arr;
3.dataType arr[];
Instantiation of an Array in Java
1.array RefVar= newdatatype[siz e];
Example of Java Array
Let's seethesimple example ofjava array, where wearegoing to
declare, instantiate, initialize and traverse an array.
class Testarray{
public static void main(String args[]){
inta[]=newint[5];//declaration andinstantiatio n
a[0]=10;//initialization a
[1]=20;
a[2]=70;
a[3]=90;
a[4]=10;
//traversing arraymunotes.in
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113for(inti=0;iSystem.out.println(a[i]);
}}
Output:
10
20
70
90
10
Declaration, Instantiation and Initialization of Java A rray
Wecandeclare, instantiate andinitialize thejava array together by:
inta[]={33,3,4,5,6};//declaration, instantiation and initialization Let's see
the simple example toprint this array.
//Java Program toillustrate theuseofdeclaration, instan tiation
//and initialization of Java array in asingle line
class Testarray1{
public static void main(String args[]){
inta[]={33,3,4,5,6};//declaration, instantiation andinitialization
//printing array
for(inti=0;iSystem.out.println(a[i]);
}}
Output:
33
3
4
5
6
8.3.1 Multidimensional Array in Java
In such case, data isstored inrowandcolumn based index (also known as
matrix form).
Syntax to Declare Multidimensional Array in Java
1.dataTyp e[][] arrayRefVar;
2.dataType [][]arrayRefVar;
3.dataType arrayRefVar[][];
4.dataType []arrayRefVar[];munotes.in
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114Example to instantiate Multidimensional Array in Java
int[][]arr=new int [3][3];//3 rowand3 column
Example to initialize Multidimensional Array in Jav a
arr[0][0]=1;
arr[0][1]=2;
arr[0][2]=3;
arr[1][0]=4;
arr[1][1]=5;
arr[1][2]=6;
arr[2][0]=7;
arr[2][1]=8;
arr[2][2]=9;
Example of Multidimensional Java Array
Let's see the simple example to declare, instantiate, initialize and print the
2Dimensional array.
//Java Program toillustrate theuseof multidimensional array
class Testarray3
{
public static void main(String args[])
{
//declaring andinitializing 2Darray
intarr[][]={{1,2,3},{2,4,5},{4,4,5}};
//printing 2Darray
for(inti=0;i<3;i++){
for(intj=0;j<3;j++){
System.out.print(arr[i][j]+" ");
}
System.out.println();
}
}}
Output:
1 23
2 45
4 45
8.4 JAVA -VECTOR CLASS
Vector implements adynamic array. Itissimilar toArray Lis t,but
with twodifferences −
Vector issynchronized.munotes.in
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115Vector contains many legacy methods that are not part of the
collections framework.
Vector proves tobevery useful ifyoudon't know thesize ofthearray
inadvance oryoujustneed onethatcan change sizes over the lifetime of
aprogram.
Following is the list of constructors provided by thevector class.
Sr.No. Constructor & Description
1 Vector( )
This constructor creates a default vector, which has aninitial
sizeof10.
2 Vector(int size)
This constructor accepts anargument that equals tothe
required size, and creates avector whose initial capacity is
specified bysize.
3 Vector(Collection c)
This constructor creates a vector thatcontains the elements of
collection c.
4 Vector(int size, intincr)
This constructor cr eates a vector whose initial capacity is
specified by size and whose increment is specified by incr.
The increment specifies the number of elements to allocate
each time that a vector is resized upward.
Apart from themethods inherited from itsparent classes, Vector
defines thefollowing methods
−
Sr.No. Constructor & Description
1 void add(int index, Object element)
Inserts thespecified element at thespecified position inthis
Vector.
2 boolean add(Object o)
Appends thespecified element to theendofthisVector.
3 boolean addAll(Collection c)
Appends all of the elements in the specified Collection to the
end of this Vector, in the order that they are returned by the
specified Collection's Iterator.
4 boolean addAll(int index, Collection c)
Inserts alloftheelements ininthespecified Collection into
thisVector atthespecified position.munotes.in
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1165 void addElement(Object obj)
Adds thespecified component totheend ofthis vector,
increasing itssizeby one.
6 intcapacity()
Returns thecurrent capacity ofthisvector.
7 void clear()
Removes alloftheelements from thisvector.
8 Object clone()
Returns aclone ofthisvector.
9 boolean contains(Object elem)
Tests ifthespecified object is acomponent in thisvector.
10 boolean containsAll(Collection c)
Returns true ifthis vector contains alloftheelements in
thespecified Collection.
11 void copy Into(Object[] anArray)
Copies thecomponents ofthisvector intothespecified array.
12 Object elementAt(int index)
Returns thecomponent at the specified index.
13 Enumeration elements()
Returns anenumeration ofthecomponents ofthisvector.
14 void ensure Capacity(int minCapacity)
Increases the capacity of this vector, if necessary, to ensure
that it can hold atleast thenumber ofcomponents specified
bythe minimum capacity argument.
15 boolean equals(Object o)
Compares thespecified Object with thisvector forequality.
16 Object firstElement()
Returns thefirst component (the item at index 0)ofthis
vector.
17 Object get(int index)
Returns theelement atthespecified position inthisvector.
18 inthash Code()
Returns thehash code value for this vector.
19 intindex Of(Object elem)
Searches forthefirst occurence ofthegiven argument,
testing forequality using theequals method.munotes.in
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11720 intindex Of(Object elem, intindex)
Searches forthefirst occurence ofthegiven argument,
beginning thesearch atindex, andtesting forequality using
theequals method.
21 void insert Element At(Object obj,intindex)
Inserts thespecified object asacomponent inthisvector at
thespecified index.
22 boolean is Empty()
Tests ifthisvector hasnocomponents.
23 Object lastElement()
Returns thelast component of thevector.
24 intlastIndexOf(Object elem)
Returns theindex ofthelast occurrence ofthespecified
object inthisvector.
25 intlastIndex Of(Object elem, intindex)
Searches backwards forthespecified object, starting from
thespecified index, andreturns an index toit.
26 Object remove(int index)
Removes theelement atthespecified position inthisvector.
27 boolean remove (Object o)
Removes thefirst occurrence ofthespecified element in
this vector, Ifthevector does notcontain theelement, itis
unchanged.
28 boolean remove All(Collection c)
Removes from this vector allofitselements that are
contained inthespecified Collection.
29 void remove AllElements()
Removes allcomponents from thisvector andsetsitssizeto
zero.
30 boolean remove Element(Object obj)
Removes the first (lowest -indexed) occurrence ofthe
argument from thisvector.
31 void remove Element At(intindex)
remove Element At(int index).
32 protected void remove Range (int from Index, intto
Index)
Removes from this List alloftheelements whose index
isbetween from Index, inclusive and toIndex, exclusive.munotes.in
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11833 boolean retainAll(Collection c)
Retains only theelements inthisvector thatarecontained in
thespecified Collection.
34 Object set(int index, Object element)
Replaces the element atthe specified position inthis
vector with thespecified element.
35 void setElement At(Object obj,intindex)
Sets thecomponent atthespecified index ofthis vector
tobethe
36 specified object.
37 void setSize(intnewSize)
Setsthesizeofthis vector.
38 intsize()
Returns thenumber ofcomponents inthisvector.
39 ListsubList(intfrom Index, inttoIndex)
Returns aview oftheportion ofthis List between from
Index, inclusive, andtoIndex, exclusive.
40 Object[] toArray()
Returns anarray containing alloftheelements inthis
vector inthecorrect order.
41 Object[] toArray(Object[] a)
Returns an array containing all of the elements in this vector
in the correct order; the runtime type of the returned array is
that of the specified array.
42 String toString()
Returns astring representation ofthis vector, containing
theString representation of each element.
Example
The following program illustrates several ofthemethods supported by
this
collection –
import java.util.*;
public class VectorDemo
{
public static void main(String args[]){
// initi al size is 3, increment is 2
Vector v =new Vector(3,2);
System.out.println("Initial size: "+ v.size());munotes.in
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119System.out.println("Initial capacity: "+ v.capacity());
v.addElement(newInteger(1));
v.addElement(newInteger(2));
v.addElement(newInteger(3));
v.addElem ent(newInteger(4));
System.out.println("Capacity after four additions: "+
v.capacity());
v.addElement(newDouble(5.45));
System.out.println("Current capacity: "+ v.capacity());
v.addElement(newDouble(6.08));
v.addElement(newInteger(7));
System.out.println(" Current capacity: "+ v.capacity());
v.addElement(newFloat(9.4));
v.addElement(newInteger(10));
System.out.println("Current capacity: "+ v.capacity());
v.addElement(newInteger(11));
v.addElement(newInteger(12));
System.out.println("First element:
"+(Integer )v.firstElement());
System.out.println("Last element:
"+(Integer)v.lastElement());
if(v.contains(newInteger(3))) System.out.println("Vector
contains 3.");
// enumerate the elements in the vector.
Enumeration vEnum = v.elements();
System.out.println(" \nElements in vector:");
while(vEnum.hasMoreElements())
System.out.print(vEnum.nextElement()+" ");
System.out.println();
}
}
This willproduce thefollowing result –
Output :
Initial size: 0
Initial capacity: 3
Capacity after four additions: 5 Current capa city: 5
Current capacity: 7
Current capacity: 9
First element: 1
Last element: 12
Vector contains 3.munotes.in
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120Elements in vector:
12345 . 4 56 . 0 879 . 41 01 11 2
8.5 SAMPLE QUESTIONS
Q1. What is the need of Array ? Explain
Q2.What is Array ? Explain with Examp le.
Q3.What is Array ? what are the Types of Array ?
Q4.What are the Advantages of Vector Class over Java Array ?
Q5. What is vector ? Explain with Example.
Q6. Explain various methods vectors.
Q7. What is the difference between Array and Vector ?
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1219
MULTITHREADING
Unit Structure :
9.0 Introduction
9.1 Objectives
9.2 Multithreading in Java
9.2.0 Advantages of Java Multithreading
9.3 Multitasking
9.4 What is Thread in java
9.5 Java Thread class
9.6 Life cycle ofaThread (Thread States)
9.7 Thread class
9.8 Synchronization in Java
9.9 Mutual Exclusive
9.10 Sample Questions
9.0 INTRODUCTION
A thread is single sequence of execution that can run
independently in an application. This unit covers the very important
concept of multithreading in pr ogramming. Uses of thread in programs
are good in terms of resource utilization of the system on which
application is running. Multithreaded programming is very useful in
network and Internet applications development. In this unit you will learn
what is m ultithreading, how thread works, how to write programs in Java
using multithreading. Also, in this unit will be explained about thread -
properties, synchronization, and interthread communication.
9.1 OBJECTIVES
After going through this unit, you will be a ble to:
describe the concept of multithreading;
explain the Java thread model;
create and use threads in program;
describe how to set the thread priorities;
use the concept of synchronization in programming, and
use inter -thread communication in programs.munotes.in
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1229.2 MULTITHREADING IN JAVA
Multithreading in java isaprocess ofexecuting multiple threads
simultaneously.
Thread isbasically alightweight sub-process, asmallest unit of
processing. Multiprocessing andmultithreading, both are used toachieve
multitasking.
But we use multithreading than multiprocessing because threads
share a common memory area. They don't allocate separate memory area
sosaves memory, andcontext -switching between thethreads takes less
time than process.
Java Multithreading ismostly used ingames, animation etc.
9.2.0 Advantages of Java Multithreading
1)Itdoesn't block theuser because threads areindependent and you can
perform multiple operations atsame time.
2)You canperform many operations together soitsaves time.
3)Threads areindependent soitdoesn't affect other threads if
exception occur inasingle thread.
9.3 MULTITASKING
Multitasking is a process of executing multiple tasks
simultaneously. We use multitasking to utilize the CPU. Multitasking can
be achieved by two ways:
Process -based Multitasking(Multiprocessing)
Thread -based Multitasking(Multithreading)
1)Process -based Multitasking (Multiprocessing)
Each process have itsown address inmemory i.e.each process
allocates separate memory area.
Process isheavyw eight.
Cost ofcommunication between theprocess ishigh.
Switching from oneprocess toanother require some time forsaving
andloading registers, memory maps, updating lists etc.
2)Thread -based Multitasking (Multithreading)
Threads share thesame address space.
Thread islightweight.
Cost ofcommunication between thethread islow.munotes.in
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1239.4 WHAT IS THREAD IN JAVA
Athread isalightweight sub process, asmallest unit of
processing. Itisaseparate path ofexecution.
Threads are independent, if there occur s exception in one thread, it
doesn't affect other threads. Itshares a common memory area.
9.5 JAVA THREAD CLASS
Thread class is the main class on which java's multithreading system is
based. Thread class provide constructors and methods to create an d
perform operations on a thread. Thread class extends Object class and
implements Runnable interface.
Java Thread Methods
S.N. Modifie ra n d
TypeMethod Description
1 void start() Itisused tostart the
execution ofthethread.
2 void run() Itisused toperform action for
athread.
3 static void sleep() It sleeps a thread forthe
specified amount of time.munotes.in
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1244 static Thread current
Thread()Itreturns areference to
thecurrently executing thread
object.
5 void join() Itwaits for athread todie.
6 int getPriority() Itreturns thepriority ofthe
thread.
7 void setPriority() Itchanges thepriority of the
thread.
8 String getName() Itreturns thename ofthe
thread.
9 void setName() Itchanges thename ofthe
thread.
10 long getId() Itreturns theidofthethread.
11 boolean isAlive() Ittests if thethread is alive.
12 static void yield() It causes the currently
executing thread objectto
temporarily pause and allow
other threads toexecute.
13 void suspend() It is used to suspend the
thread.
14 void resume() It is used to resume the
suspended thread.
15 void stop() It is used to stop the thread.
16 void destroy() It is used to destroy the thread
group and all of its subgroups.
17 boolean isDaemon() It tests if the thread is a
daemon thread.
18 void set
Daemon()It marks the thread as daemon
or user thread.
19 void interrupt() It interrupts the thread.
20 boolean is
interrupted()It tests whether the thread has
been interrupted.
21 static boolean interrupted() It tests whet her the current
thread has been interrupted.
22 static int active
Count()It returns the number of active
threads in the current thread's
thread group.munotes.in
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12523 void check
Access()It determines if the currently
running thread has permission
to modify the thread.
24 static boolean hold Lock() It returns true if and only if
the current thread holds the
monitor lock on the specified
object.
25 static void dump
Stack()It is used to print a stack trace
of the curr ent thread to the
standard error stream.
26 Stack Trace
Elemen t[]get Stack
Trace()It returns an array of stack
trace elements representing
the stack dump of the thread.
27 static int enumerate() It is used to copy every active
thread's thread group and its
subgroup into the specified
array.
28 Thread. State getState() It is used to return the state of
the thread.
29 Thread Group get Thread
Group( )It is used to return the thread
group to which this thread
belongs
30 String toString() It is used to return a string
representation of this thread,
including the thread's name,
priority, and thread group.
31 void notify() It is used to give the
notification for only one
thread which is waiting for a
particular object.
32 void notify All() It is used to give the
notification to all waiting
threads of a particular object.
9.6 LIFE CYCLE OF A THREAD ( THREAD STATES )
Athread can beinone ofthefive states. According tosun,
there isonly 4states inthread life cycle in java new, run nable, non -
runnable and terminated. There is no running state.
Butforbetter understanding thethreads, weareexplaining it in the
5 states.munotes.in
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126The life cycle of the thread in java is controlled by JVM. The java
thread states are as follows:
1.New
2.Runnable
3.Running
4.Non-Runnable (Blocked)
5.Terminated
1)New
Thethread isinnew state ifyoucreate aninstance ofThread class
butbefore theinvocation ofstart() method.
2)Runnable
Thethread isinrunnable state after invocation ofstart() method, but
thethrea dscheduler hasnotselected ittobetherunning thread.
3)Running
Thethread isinrunning state ifthethread scheduler hasselected it.
4)Non-Runnable (Blocked)
This isthestate when thethread isstill alive, but is currently not
eligible torun.
5)Term inated
Athread is interminated ordead state when itsrun() method exits.
How to create thread
There aretwoways tocreate a thread:
1.Byextending Thread class
2.Byimplementing Runnable interface.
9.7 THREAD CLASS
Thread class provide constructors and methods tocreate and
perform operations onathread. Thread class extends Object class and
implements Runnable interface.munotes.in
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127Commonly used Constructors ofThread class:
Thread()
Thread(String name)
Thread(Runnable r)
Thread(Runnable r,String name)
Commonl yused methods ofThread class:
1.public void run(): isused toperform action fora thread.
2.public void start(): starts the execution of the thread.JVM calls the
run() method onthethread.
3.public void sleep (long miliseconds): Causes the currently
executi ngthread to sleep (temporarily cease execution) for the
specified number of milliseconds.
4.public void join(): waits forathread todie.
5.public void join(long miliseconds): waits forathread todieforthe
specified miliseconds.
6.public intgetPriority() :returns thepriority ofthethread.
7.public intsetPriority(int priority): changes thepriority ofthe
thread.
8.public String getName(): returns thename ofthethread.
9.public void setName(String name): changes thename ofthe
thread.
10.public Thread curren tThread(): returns the reference of currently
executing thread.
11.public intgetId(): returns theidofthethread.
12.public Thread.State getState(): returns thestate ofthethread.
13.public boolean isAlive(): tests ifthethread is alive.
14.public void yield(): causes the currently executing thread
object totemporarily pause and allow other threads to execute.
15.public void suspend(): isused tosuspend thethread (depricated).
16.public void resume(): isused toresume the suspended
thread(depricated).
17.public void stop(): isused to stop thethread (depricated).
18.public boolean is Daemon(): tests ifthethread is adaemon thread.
19.public void setDaemon (boolean b):marks thethread asdaemon
oruserthread.
20.public void interrupt(): interrupts thethread.
21.public boole anisInterrupted(): tests ifthethread has been
interrupted.munotes.in
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12822.public static boolean interrupted(): tests ifthecurrent thread
hasbeeninterrupted.
1) Java Thread Example by extending Thread class
class Multi extends Thread
{
public void run()
{
System .out.println("thread is running...");
}
public static void main(String args[])
{
Multi t1=newMulti();
t1.start();
}
}
Output: thread isrunning...
9.8 SYNCHRONIZATION IN JAVA
Synchronization injava isthecapability tocontrol theaccess of
multiple threads toanyshared resource .
Java Synchronization isbetter option where we want toallow
only onethread toaccess theshared resource.
Why use Synchronization ?
Thesynchronization ismainly used to
1.Toprevent thread interference.
2.Topreven tconsistency problem.
Types ofSynchronization
There aretwotypes of synchronization
1.Process Synchronization
2.Thread Synchronization
Here, wewilldiscuss only thread synchronization.
Thread Synchronization
There aretwotypes ofthread synchronization mutual exclusive andinter-
thread communication.
Mutual Exclusive
Synchronized method.
Synchronized block.
static synchronization.
Cooperation (Inter -thread communication injava)munotes.in
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1299.9 MUTUAL EXCLUSIVE
Mutual Exclusive helps keep threads from interfering with oneanother
while sharing data. This canbedone bythree ways in java:
bysynchronized method
bysynchronized block
bystatic synchronization
class Table{
void printTable( intn){//method not synchronized
for(inti=1;i<=5;i++){
System.out.println (n*i);
try{
Thread.sleep(400);
}
catch (Exception e)
{
System.out.println(e);
}}}}
class MyThread1 extends Thread{
Table t;
MyThread1(Table t){
this.t=t;
}
public void run(){
t.printTable(5);
}}
class MyThread2 extends Thread{
Table t;
MyThread2(Table t){
this.t=t;
}
public void run(){
t.printTable(100);
}
}
class TestSynchronization1{
public static void main(String args[]){
Table obj=newTable();//only oneobject
MyThread1 t1=newMyThread1(obj);
MyThread2 t2=newMyThread2(obj);munotes.in
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130t1.start();
t2.start();
}}
Output:
5
100
10
200
15
300
20
400
25
500
9.10 SAMPLE QUESTIONS
Q1. How does multithreading take place on a computer with a single
CPU?
Q2.State the advantages of multithreading.
Q3.Explain how a thread is created by extending the Thread class.
Q4.Explain Lifecycle of Thread.
Q5.Explain the need of synchronized method
Q6. List And Explain Various Methods of Thread
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13110
EXCEPTIONS
Unit Structure :
10.0 Introduction
10.1 Objectives
10.2 Exception Handling in Java
10.3 Hierarchy of Java Exception classes
10.4 Types of Exception
10.5 Common scenarios where exceptions may occur
10.6 Java Exception Handling Keyword s
10.7 Java try block
10.8 Java catch block
10.9 Java finally block
10.10 Java throw exception
10.11 Java throws keyword
10.12 Difference between throw and throws in Java
10.13 Sample Questions
10.0 INTRODUCTION
During programming in languages like c, c++ you might have
observed that even after successful compilation some errors are detected
at runtime. For handling these kinds of errors there is no support from
programming languages like c, c++. Some error handling mechanisms
like returning special val ues and setting flags are used to determine that
there is some problem at runtime. In C++ programming language there is
a very basic provision for exception handling. Basically exception
handlings provide a safe escape route from problem or clean -up of err or
handling code. In Java exception handling is the only semantic way to
report error .In Java exception is an object, which describes error
condition, occurs in a section of code. In this unit we will discuss how
exceptions are handled in Java, you will a lso learn to create your own
exception classes in this unit.
10.1 OBJECTIVES
After going through this unit you will be able to:
describe exception;
explain causes of exceptions;
writing programs with exceptions handling;munotes.in
Page 132
132use built –in exceptions;
create y our own exception classes.
10.2 EXCEPTION HANDLING IN JAVA
The exception handling injava isone ofthe powerful
mechanism tohandle theruntime errors sothat normal flow of the
application canbe maintained.
Inthis page, wewill learn about java exception, itstype and
thedifference between checked andunchecked exceptions.
What is exception
Dictionary Meaning: Exception isanabnormal condition.
Injava, exception isanevent that disrupts thenormal flow ofthe
program. Itisanobject which isthrown atruntime.
What is exception handling
Exception Handling isamechanism tohandle runtime errors such as
Class NotFound, IO,SQL, Remote etc.
Advantage of Exception Handling
The core advantage of exception handling is to maintain the
normal flow of the application . Exception normally disrupts the normal
flow of the application that is why weuseexception handling. Let's take a
scenario:
1.statement 1;
2.statement 2;
3.statement 3;
4.statement 4;
5.statement 5;//exception occurs
6.statement 6;
7.statement 7;
8.statement 8;
9.statement 9;
10.statement 10;
Suppose there is 10 statements in your program and there occurs
an exception at statement 5, rest of the code will not be executed i.e.
statement 6 to 10 will not run. If we perform exception handling, rest of
the st atement will be executed. That is why we useexception handling in
java.munotes.in
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13310.3 HIERARCHY OF JAVA EXCEPTION CLASSES
10.4 TYPE OF EXCEPTION
There are mainly two types of exceptions: checked and unchecked
where error is considered as unchecked excep tion. The sun micro system
says there are three types of exceptions:
1.Checked Exception
2.Unchecked Exception
3.Error
Difference between checked andunchecked exceptions
1)Checked Exception
The classes that extend Throwable class except Runtime
Exception and Er ror are known aschecked exceptions e.g. IOmunotes.in
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134Exception, SQL Exception etc. Checked exceptions arechecked at
compile -time.
2)Unchecked Exception
The classes that extend Runtime Exception are known as
unchecked exceptions e.g. Arithmetic Exception, Null Point erException,
Array Index OutOfBounds Exception etc.Unchecked exceptions are not
checked at compile -time rather they are checked at runtime.
3)Error
Error isirrecoverable e.g.out of Memory Error, Virtua Machine
Error, Assertion Error etc.
10.5 COMMOM SCENARIOS WHERE EXCEPTION
MAY OCCUR
There aregiven some scenarios where unchecked exceptions
canoccur. They areasfollows:
1)Scenario where Arithmetic Exception occurs
Ifwedivide anynumber by zero, there occurs anArithmetic Exception.
1.inta=10/0;//ArithmeticException
2)Scenario where Null Pointer Exception occurs
Ifwehave null value inanyvariable, performing anyoperation
bythevariable occurs anNull Pointer Exception.
1. String s=null;
2. System.out.println (s.length());//Null Pointer Exception
3)Scenario where Number Format Exception occurs
The wrong formatting ofany value, may occur Number
Format Exception. Suppose Ihave a string variable that have characters,
converting this variable into digit will occur Number Format Exception.
1.String s="abc";
2.inti=Integer.parseInt(s);//Number Format Exception
4)Scenario where Array Index OutOfBounds Exception occurs
Ifyou areinser ting any value in the wrong index, it would result
Array Index OutOfBounds Exception as shown below:
1.inta[]=newint[5];
2.a[10]=50; //Array Index OutOfBounds Exceptionmunotes.in
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13510.6 JAVA EXCEPTION HANDLING KEYWORDS
There are5k e y w o r d s used in java exception handling.
1.try
2.catch
3.finally
4.throw
5.throws
10.7 JAVA TRY BLOCK
Java tryblock isused toenclose thecode that might throw an
exception. Itmust beused within themethod.
Java tryblock must befollowed byeither catch or finally block.
Syntax ofjava try-catch
try{
//code thatmay throw exception
}catch (Exception_class_Name ref){}
Syntax oftry-finally block
try{
//codethatmay throw exception
}finally {}
10.8 JAVA CATCH BLOCK
Java catch block isused tohandle theException. Itmust be
used after thetryblock only.
You canusemultiple catch block with asingle try.
Problem without exception handling
Let's trytounderstand theproblem ifwedon't usetry-catch block.
public class Testtrycatch1{
public static void main(String args[]){
intdata=1 0/0;//may throw exception
System.out.println("rest of the code...");
}
}
Output:
Exception inthread main java.lan g.Arithmetic Exception:/ byzeromunotes.in
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13610.9 JAVA FINALLY BLOCK
Java finally block isablock that isused toexecute important
code such asclosing connection, stream etc.
Java finally block is always executed whether exception is
handled or not. Java finallyblock follows try
Usage of Java finally
Let's see thedifferent cases where java finally block canbeused.
Case 1
Let's seethejavafinally example where exception doesn't occur .
class Test Finally Block{
public static void main(String args[]){
try{
intdata=25/5;
System.out.println(data);
}
catch (Nul Pointer Exception e){System.out.println(e);}
finally {System.out.println("finally block isalways executed");}
System.out.println("rest ofthecode...");
}
}
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137Output:5
finally block is always exe cuted restof the code...
10.10 JAVA THROW EXCEPTION
Java throw keyword
TheJava throw keyword isused to explicitly throw anexception.
We can throw either checked or uncheked exception in java by
throw keyword. The throw keyword ismainly used tothrowcustom
exception. Wewillseecustom exceptions later.
Thesyntax ofjavathrow keyword isgiven below.
throw exception;
Let's seetheexample ofthrow IOException.
throw new IOException("sorry device error);
java throw keyword example
In this ex ample, we have created the validate method that takes
integer value as a parameter. Iftheageislessthan 18,wearethrowing
theArithmetic Exception otherwise print amessage welcome tovote.
public class TestThrow1{
static void validate( intage){
if(age<18)
throw newArithmetic Exception(" Agenotvalid");
else
System.out.println("welcome You can vote");
}
public static void main(String args[]){
validate(12 );
System.out.println("rest ofthecode...");
}
}
Output:
Exception inthread main java.lang. Arithmetic Exception:not valid
10.11 JAVA THROWS KEYWORD
The Java throws keyword is used to declare an exception. It
gives an information to theprogrammer that there may occur anmunotes.in
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138exception soitisbetter fortheprogrammer toprovide theexception
handling code sothatnormal flow can be maintained.
Exception Handling ismainly used tohandle the checked
exceptions. Ifthere occurs anyunchecked exception such asNull Pointer
Exception, itisprogrammers fault that heisnotperforming check up
befor ethecode being used.
Syntax of java throws
return_type method_name() throws exception_class_name{
//method code }
Which exception should be declared ?
Ans:checked exception only, because:
unchecked Exception: under your control socorrect your code.
error: beyond your control e.g. you areunable todoanything if
there occurs Virtual Machine Error or Stack Over flow Error.
Advantage of Java throws keyword
Now Checked Exception canbepropagated (forwarded incall
stack). Itprovides information tothecaller ofthemethod about the
exception
Java throws example
Let's seetheexample ofjava throws clause which describes
thatchecked exceptions canbepropagated bythrows keyword.
import java.io.IOException;
class Testthrows1{
void m()throws IOEx ception{
throw new IOException("device error");//checked exception
}
void n()throws IOException{
m();
}
void p(){
try{
n();
}catch (Exception e){System.out.println("exception handled");}
}
public static void main(String args[]){
Testthrows1 obj=newTestthrows1();munotes.in
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139obj.p();
System.out.println("normal flow...");
}
}
Output:
exception handled normal flow...
10.12 DIFFRENCE BETWEEN THROW AND THROWS
IN JAVA
There aremany differences between throw andthrows keywords. Alist
ofdifferences between throwand throws are given below:
Sr.No throw throws
1 Java throw keyword is used
to explicitly throw an
exception.Java throws keyword is used to
declare exception.
2 Checked exception cannot
propagated using throw
only.Checked exception can be
propagate d with throws.
3 Throw is followed by an
instance.Throws is followed by class.
4 Throw is used within the
method.Throws is used with the
method signature.
5 You cannot throw multiple
exceptions.You can declare multiple
exceptions eg. public void
method()throws IO Exception,
SQL Exception.
10.13 SAMPLE QUESTIONS
Q1. What is an exception? Write any three actions that can be taken after
an exception occurs in a program.
Q2.Write a program to catch more than two exceptions.
Q3.Write a partial progr am to show the use of finally clause.
Q4.Differentiate between checked and unchecked exceptions.
Q5.Explain how you can throw an exception from a method in Java.
Q6.Write a program to create your own exception subclass that throws
exception if the sum of twointegers is greater that 99.
Q7.Draw and Explain Exception class Hirerchy in detail.
Q8.Differentiate between throw and throws exceptions / Keywords.
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14011
BYTE STREAMS
Unit Structure :
11.0 Introduction
11.1 Objectives
11.2 Java I/O Tutorial
11.3 Stream
11.4 Output Stream vs Input Stream
11.5 Output Stream class
11.6 Input Stream class
11.7 Java File Output Stream Class
11.8 Java File Input Stream Class
11.9 Java Byte Array Output Stream Class
11.10 Java Byte Array Input Stream Class
11.11 JavaC h a r Array Writer Class
11.12 Java File Class
11.13 Reading and Writing Files
11.14 Sample Questions
11.0 INTRODUCTION
Input is any information that is needed by a program to complete
its execution. Output is any information that the program must conve y to
the user. Input and Output are essential for applications development. To
accept input a Java program opens a stream to a data source, such as a file
or remote socket, and reads the information serially. Whether reading data
from a file or from a sock et, the concept of serially reading from, and
writing to, different data sources is the same. For that very reason, it is
essential to understand the features of top -level classes (Java.io.Reader,
Java.io.Writer). In this unit you will be working on some b asics of I/O
(Input –Output) in Java such as Files creation through streams in Java
code. A stream is a linear, sequential flow of bytes of input or output data.
Streams are written to the file system to create files. Streams can also be
transferred over th e Internet. In this unit you will learn the basics of Java
streams by reviewing the differences between byte and character streams,
and the various stream classes available in the Java.io package. We will
cover the standard process for standard Input (Read ing from console) and
standard output (writing to console).munotes.in
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14111.1 OBJECTIVES
After going through this unit you will be able to:
explain basics of I/O operations in Java;
use stream classes in programming;
take inputs from console;
write output on console ;
read from files, and
write to files.
11.2 JAVA I/O TUTORIAL
Java I/O(Input andOutput) is used toprocess the input andproduce the
output .
Java uses theconcept of a stream tomake I/Ooperation fast. The
java.io package contains alltheclasses required for input and output
operations.
Wecanperform filehandling in Java byJava I/O API.
11.3 STREAM
Astream isasequence ofdata. In Java, astream iscomposed of
bytes. It's called astream because it is like astream of water thatcontinues
toflow.
InJava, 3streams arecreated forus automatically. Allthese
streams areattached with theconsole.
1)System.out: standard output stream
2)System.in: standard input stream
3)System.err: standard error stream
Let's seethecode toprint output andanerror message totheconsole.
System.out.println("simple message");
System.err.println("error message");
Let's seethecode togetinput from console.
inti=System.in.read();//returns ASCII code of1stcharacter
System.out.println(( char)i);//will printthecharactermunotes.in
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14211.4 OUTPUT STREAM VS INPUT STREAM
The explanation ofOutput Stream and Input Stream classes are
given below:
Output Stream
Java application uses anoutput stream towrite data toa
destination; itmay beafile,anarray, peripheral device or socket.
Input Stream
Java application uses aninput stream toread data from a source; it
may be a file, an array, peripheral device orsocket.
Let's understand the working ofJava Output Stream and Input
Stream by thefigure given below.
11.5OUTPUT STREAM
Output Stream class is an abstract class. It is the super class of all
classes representing an output stream of bytes. An output stream accepts
output bytes and sends them to some sink.
Useful methods of Output Stream
Method Description
public void write(int)throws
IOExceptionisused towrite abyte tothecurrent
output stream.
public void write(byte[])throws
IOExceptionisused towrite anarray ofbyte to
thecurrent output stream.
public void flush()throws
IOExceptionflushes thecurrent output stream.
public void close()throws
IOExceptionisused to close thecurrent output
stream.
11.6 INPUT STREAM CLASS
Input Stream class isanabstract class. Itisthesuperclass of all
classes representing aninput stream of bytes.munotes.in
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143Useful methods of Input Stream
Method Description
public abstract int read()throws IO
Exceptionreads thenext byte ofdata from the
input stream. Itreturns -1a ttheend
of the file.
public int available()throws IO
Exceptionreturns anestimate ofthenumber
ofbytes thatcanberead from the
current input stream.
public void close()throws IO
Exceptionisused to close thecurrent input
stream.
11.7 JAVA FILE OUTPUT STREAM CLASS
Java FileOutput Stream is an output stream used for writing data to afile.
If you have to write primitive values into a file, use File Output
Stream class. You can write byte -oriented as well as character -oriented
data through File Output Stream class. But, for character -oriented data, it
is preferred to use FileWriter than FileOutput Stream.
FileOutput Stream class declaration
Let's seethedeclaration forJava.io.File Output Stream class:
1.public class FileOutput Stream extends Output Stream
FileOutput Stream class methods
Method Description
protected void finalize() Itisused toclean uptheconnection
with thefileoutput stream.
void write(byte[] ary) It is used to write ary.length bytes
from the byte array to the fileoutput
stream.
void write(byte[] ary, intoff,int
len)Itisused to write lenbytes from the
byte array starting atoffset offto the
fileoutput s tream.
void write(int b) Itis used to write thespecified byte
tothefileoutput stream.
FileChannel getChannel() Itisused toreturn thefilechannel
object associated with thefileoutput
stream.
FileDescriptor getFD() It is used to return the file descriptor
associated with thestream.
void close() Itisused tocloses the file output
stream.munotes.in
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144Java FileOutputStream Example 1:write byte
import java.io.FileOutputStream;
public class FileOutputStreamExample {
public static void main(String args[ ]){
try{
FileOutputStream fos=newFileOutputStream("D: \\test.txt");
fos.write(65);
fos.close();
System.out.println("success...");
}
catch (Exception e)
{System.out.println(e);}
}
}
Output:
Success...
The content of a text file test.txtis set with the d ataA.test.txt
A
Java FileOutputStream example 2:write string
import java.io.FileOutputStream;
public class FileOutputStreamExample {
public static void main(String args[]){
try{
FileOutputStream fos=newFileOutputStream("D: \\test.txt");
String s="Welco metojava.";
byte b[]=s.getBytes();//converting string into byte array
fos.write(b);
fos.close();
System.out.println("success !check text file ...");
}catch (Exception e){System.out.println(e);}
}
}
Output:
Success...
Thecontent of a text file test.txtis set with the data Welcome to java.
test.txt
Welcome tojava.munotes.in
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14511.8 JAVA FILEINPUTSTREAM CLASS
Java File Input Stream class obtains input bytes from a file.I ti s
used for reading byte -oriented data (streams of raw bytes) such as image
data, audio, video etc. You can also read character -stream data. But, for
reading streams ofcharacters, itisrecommended touseFileRead erclass.
Java FileInput Stream class declaration
Let's seethedeclaration forjava.io.File Input Stream class:
1.public class FileInput Stream extends Input Stream
Java FileInput Stream class methods
Method Description
intavailable() Itisused toreturn theestimated
number ofbytes thatcanberead from
theinput stream.
intread() Itisused toread the byte of data
from theinput stream.
intread(byte[] b) Itisused toread uptob.length bytes
ofdata from theinput stream.
int read(byt e[] b, int off,int len) It is used to read up to lenbytes of
data from the input stream.
long skip(long x) It is used to skip over and discards x
bytes of data from the input stream.
FileChannel get Channel() Itisused toreturn theunique File
Chann el object associated with the
fileinput stream.
FileDescriptor getFD() Itisused toreturn theFileDescriptor
object.
protected voidfinalize() Itisused to ensure that theclose
method is call when there isno more
reference to the fileinput stream.
void close() Itisused to closes the stream .
11.9 JAVA BYTE ARRAY OUTPUT STREAM CLASS
Java Byte Array Output Strea mclass isused towrite common
data intomultiple files. In thisstream, thedata is written into a byte array
which can be written to multiple streams later.
TheByte Array Output Stream holds acopy ofdata and forwards
ittomultiple streams. The buffer of Byte Array Output Stream
automatically grows according to data.munotes.in
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146Java Byte Array Output Stream class declaration
Let's seethedeclaration forJava.io.Byte Array Output Stream class:
1.publicclass Byte Array Output Stream extends Output Stream
Java Byte Array Output Stream class constructors
Constructor Description
Byte Array Output Stream() Creates a new byte array output
stream with the initial capacity of
32 bytes, though its size increases
if necessary.
Byte Array Output Stream (int size) Creates anew byte array output
stream, with a buffer capacity of
thespecified size, in bytes.
Java Byte Array Output Stream class meth ods
Method Description
intsize() Itisused to returns the current size of a
buffer.
byte[] toByte Array() Itisused tocreate anewly allocated byte
array.
String toString() Itis used for converting thecontent into
astring decoding bytes using aplatform
default character set.
String to String (String
charset Name)It is used for converting the content into a
string decoding bytes using aspecified
charset Name.
void write(int b) Itisused forwriting the byte specified to
thebytearray output stream.
void write(byte[] b,int
off,int lenIt is used for writing len bytes from
specified byte array starting from the offset
offto the byte array output stream.
void write To(Output
Streamout)Itisused forwriting the complete content
of abytearray output stream to the specified
output stream.
void reset() It is used to reset the count field of a byte
array output stream to zero value.
void close() Itisused toclose theByte ArrayOutput
Stream.munotes.in
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147A
AExample ofJava Byte Array Output Stream
Let's seeasimple example ofjava Byte Array Output Stream class to
write common data into2files: f1.txt and f2.txt.
import java.i o.*;
public class Data Stream Example {
public static void main(String args[]) throws Exception{
FileOutput Stream fos1=newFileOutput Stream("D: \\test1.txt");
FileOutput Stream fos2=newFileOutput Stream("D: \\test2.txt"); 7.
Byte Array Output Stream bos=newByte Array Output Stream();
bos.write(65);
bos.writeTo(fout1);
bos.writeTo(fout2);
bos.flush();
bos.close();//has no effect
System.out.println("Success...");
}
}
Output:
test1.txt:
test2.txt:
11.10 JA VA BYTE ARRAY INPUT STREAM CLASS
The Byte Array Input Stream iscomposed oftwo words: Byte
Array and Input Stream. Asthename suggests, it can be used to read byte
array as input stream.
Java Byte Array Input Stream class contains an internal buffer
which is used to read byte array asstream. In this stream, the data is read
from abyte array.
The buffer ofByte Array Input Stream automatically grows
according todata.
Java Byte Array Input Stream class declaration
Let's seethedeclaration forJava.io.Byte Array Input Stream class:
1.public class Byte Array Input Stream extends Input Stream
Java Byte Array Input Stream class constructorsSuccess...
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148Constructor Description
Byte Array Input Stream(byte[] ary) Creates anew byte array input
stream which uses aryas its buffer
array.
Byte Array Input Stream(byte[] ary,
intoffset, int len)Creates a new byte array input
stream whic huses aryasitsbuffer
array that canread uptospecified
lenbytes of data from an array.
Java Byte Array Input Stream class methods
Methods Description
intavailable() Itisused to return the number of
remaining bytes thatcanberead from the
inputstream.
intread() Itisused toread thenext byte ofdata
from theinput stream.
intread(byte[] ary, intoff,
int len)It is used to read up to len bytes of data
from an array ofbytes in the input stream.
boolean mark Supported() It is used to t est the input stream for mark
and reset method.
long skip(long x) It is used to skip the x bytes of input from
the input stream.
void mark (int read Ahead
Limit)Itisused to set the current marked
position inthe stream.
void reset() Itisused to res etthebuffer ofabyte
array.
void close() Itisused forclosing aByte Array Input
Stream.
Example ofJava Byte Array Input Stream
Let's seeasimple example ofjava Byte Array Input Stream class toread
byte array asinput stream.
import java.io.*;
public class Read Example {
public static void main(String[] args) throws IOException {
byte[] buf ={3 5 ,3 6 ,3 7 ,3 8} ;
//Create thenew byte array input stream
Byte Array Input Stream byt=newByte Array Input Stream(buf);munotes.in
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149intk=0;
while ((k=byt.read()) !=-1){
//Conversion ofabyte into character
char ch=(char)k;
System.out.println("ASCII value is:"+k+";Special character is:"+c h ) ;
}
}
}
Output:
ASCII value is:35; Specia l character is: #
ASCII value is:36; Special character is: $
ASCII value is:37; Special character is: %
ASCII value is:38; Special character is:&
Java Char Array Reader Class
The Char Array Reader iscomposed oftwo words: Char Array and
Reader. TheCharArray Reader class is used to read character array asa
reader (stream). It inherits Reader class.
Java Char Array Reader class declaration
Let's seethedeclaration forJava.io.Char Array Reader class :
1.public class Char Array Reader extends Reader
Java Char Array Reader class methods
Method Description
intread() Itisused toread asingle character
int read(char[] b, int off, int len) Itisused toread characters into the
portion ofanarray.
boolean ready() Itis used to tell whether the stream is
ready toread.
boolean mark Supported() Itisused totellwhether thestream
supports mark() operation.
long skip(long n) Itisused to skip the character inthe
input stream.
void mark(int read Ahead Limit) Itisused to mark thepresent position
inthestream.
void reset() Itisused to reset the stream to amost
recent mark.
Example ofChar Array Reader Class:
Let's seethesimple example toread a character using Java Char
Array Reader class.munotes.in
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150import java.io.CharArrayReader;
public class CharArrayExample{
public static void main(String[] ag) throws Exception
{
char[]ary={' j ' ,'a','v','a'};
CharArrayReader reader =newCharArrayReader(ary);
intk=0;
//Read until theend of afile
while ((k=reader.read()) != -1){
char ch=(char)k;
System.out.print(ch +":");
System.out.println(k);
}
}
}
Output :
j:106
a:97
v:118
a:97
11.11 JAVA CHAR ARRAY WRITER CLASS
The Char Array Writer class can be used to write common data to
multiple files. This class inherits Writer class. Its buffer automatically
grows when data iswritten inthisstream. Calling theclose() method on
thisobject has no effect.
Java Char Array Writer class declaration
Let's seethedeclaration forJava.io.Char Array Writer class:
public class Char Array Writer extends Writer
Java Char Array Writer class Methods
Method Description
intsize() Itisused toreturn thecurrent size of
thebuffer.
char[] toChar Array() Itisused toreturn thecopy ofaninput
data.
String toString() Itisused forconverting aninput data
toastring .munotes.in
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151Char Array Writer append
(char c)Itisused toappend the specified
character to the writer.
Char Array Writer append
(Char Sequence csq)Itisused toappend the specified
character sequence tothe writer.
Char Array Writer append
(Char Sequence csq, int start,
intend)It is used to append the subsequence of
aspecified character tothewriter.
void write(int c) Itisused towrite acharacter tothe
buffer.
void write(char[] c, intoff,
int len)Itisused towrite acharacter tothe
buffer.
void write(String str, int off,
intlen)Itisused towrite aportion ofstring to
thebuffer.
void write To(Writer out) Itisused towrite thecontent ofbuffer
todifferent character stream.
void flush() Itisused to flush thestream.
void reset() Itisused toreset thebuffer.
void close() Itis used to close thestream.
Example ofChar Array Writer Class:
Inthis example, we are writing a common data to 4files a.txt, b.txt, c.txt
and d.txt.
import java.io.CharArrayWriter;
import java.io.FileWriter;
public class CharArrayWriterExample {
public static void main(String args[]) throws Exception{
CharArrayWriter out=newCharArrayWriter();
out.write("Welcome tojava");
FileWriter f1=newFileWriter("D: \\testa.txt");
FileWriter f2=newFileWriter("D: \\testb.txt");
FileWriter f3=newFileWriter("D: \\testc.txt");
FileWriter f4=newFileWriter( "D:\\testd.txt");
out.writeTo(f1);
out.writeTo(f2);
out.writeTo(f3);
out.writeTo(f4);
f1.close();
f2.close();
f3.close();munotes.in
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152f4.close();
System.out.println("Success...");
}
}
Output
Success...
After executing theprogram, you can seethat allfiles have
common data: Welcome tojava.
testa.txt:
Welcome tojava
testb.txt:
c.txt:
Welcome tojava
testd.txt:
Welcome tojava
11.12 JAVA FILE CLASS
The File class is an abstract representation of file anddirectory
pathname. Apathname canbeeither absolute or relative.
TheFileclass have several methods for working with directories
andfiles such ascreating newdirectories or files, deleting and renaming
directories or files, listing the contents of a directory etc.
Fields
Modifier Type Field Description
static String path Separator It is system -dependent path -
separator character, represented as
a string for convenience.
static char path Separator
CharIt is system -dependent path -
separator character.
static String separator It is system -dependent default
name -separator character,
represented as a string for
convenience.
static char separator Char It is system -dependent default
name -separator character.munotes.in
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153Constructors
Constructor Description
File(File parent, String child) Itcreates anew Fileinstance from a
parent abstract pathname andachild
pathname string.
File(String pathname) Itcreates a new File instance by
converting the given pathname string
into an abstract pathname.
File(String parent, String child) Itcreates anew Fileinstance from a
parent pathname string and achild
pathname string.
File(URI uri) Itcreates a new File instance by
converting the given file: URI into an
abstract pathna me.
Useful Methods
Modifier and
TypeMethod Description
static File create Temp
File(String prefix,
String suffix)It creates an empty file in the
default temporary -file directory,
using the given prefix and suffix
to generate its name.
boolean create New File() It atomically creates a new,
empty file named by this
abstract pathname if and only if
a file with this name does not
yet exist.
boolean canWrite() It tests whether the application
can modify the file denoted by
this abstract pathnam e.String[]
boolean canExecute() It tests whether the application
can execute the file denoted by
this abstract pathname.
boolean canRead() It tests whether the application
can
read the file denoted by this
abstract pathname.
boolean isAbsolut e() It tests whether this abstract
pathname is absolute.munotes.in
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154boolean isDirectory() It tests whether the file denoted
by this abstract pathname is a
directory.
boolean isFile() It tests whether the file denoted
by this abstract pathname is a
normal fil e.
String getName() It returns the name of the file or
directory denoted by this
abstract pathname.
String getParent() It returns the pathname string of
this abstract pathname's parent,
or null if this pathname does not
name a parent directory.
Path toPath() It returns a java.nio.file.Path
object constructed from the this
abstract path.
URI toURI() It constructs a file: URI that
represents this abstract
pathname.
File[] listFiles() It returns an array of abstract
pathnames denoting the f iles in
the directory denoted by this
abstract pathname
long getFree Space() It returns the number of
unallocated bytes in the
partition named by this abstract
path name.
String[] list(Filename Filter
filter)It returns an array of strings
naming the files and directories
in the directory denoted by this
abstract pathname that satisfy
the specified filter.
boolean mkdir() It creates the directory named
by this abstract pathname.
Java FileExample 1
import java.io.*;
public class FileDemo {
public static void main(String[] args)
{
try{
Filefile=newFile("javaFile123.txt");
if(file.createNewFile()) {
System.out.println("New Fileiscreated!");munotes.in
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155}else{
System.out.println("File already exists.");
}
}catch (IOException e) {
e.printStackT race();
}
}
}
Output:
New Fileiscreated!
Java FileExample 2
import java.io.*;
public class FileDemo2 {
public static void main(String[] args) {
String path =" " ;
boolean bool = false;
try{
//createing new files
Filefile=newFile("testFile1.txt") ;
file.createNewFile();
System.out.println(file);
//createing newcanonical from fileobject
Filefile2 =file.getCanonicalFile();
// returns true ifthefileexists
System.out.println(file2);
bool =file2.exists();
//returns absolute pathname
path =file2.getAbsolutePath();
System.out.println(bool);
// iffileexists
if(bool) {
//prints
System.out.print(path + " Exists? " +bool);
}
}catch (Exception e){
// ifanyerror occurs
e.printStackTrace();
}
}
}munotes.in
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156testFile1.txt
/home/Work/Project/File/t
estFile1.txt true
/home/Work/Project/File/testFile1.txt Exists? trueOutput:
Java FileExample 3
import java.io. *;
public class FileExample {
public static void main(String[] args) {
Filef=newFile("/Users/test/Documents");
String filenames[]=f.list();
for(String filename:filenames){
System.out.println(filename);
}
}
}
Output:
bestreturn_orgtest.rtf BIODATA10.pa gesBIODATA1.pdf BIODATA9.png
struts2jars_test.zip workspace_test
Java FileExample 4
import java.io.*;
public class FileExample {
public static void main(String[] args) {
Filedir=newFile("/Users/Test/Documents");
Filefiles[]=dir.listFiles();
for(File file:files){
System.out.println(file.getName()+" CanWrite: "+file.canWrite()+"
IsHidden: "+file.isHidden()+" Length: "+file.length()+" bytes");
}
}
}
Output:
apache -tomcat -9.0.0.M19 Can Write: true IsHidden: false Length: 476
bytes
apache -tomcat -9.0.0 .M19.tar Can Write: true IsHidden: false Length:
13711360 bytes
bestreturn_org.rtf Can Write: true Is Hidden: false Length: 389 bytes
BIODATA10.pages Can Write: true IsHidden: false Length: 707985munotes.in
Page 157
157InputStream f=new FileInputStream("C:/java/hello");bytes BIODATA1.pdf Can Write: true Is Hidden: false Lengt h: 69681
bytes BIODATA5.png Can Write: true Is Hidden: false Length: 282125
bytes workspace Can Write: true Is Hidden: false Length: 1972 bytes
11.13 READING AND WRITING FILES
Asdescribed earlier, astream can be defined as asequence
ofdata. TheInput Stream isused to read data from a source
andtheOutput Stream isused for writing datatoadestination.
Here isahierarchy of classes todealwith Input and Output streams.
The two important streams are File Input Stream and File
Output Stream ,which would be discussed inthistutorial.
FileInput Stream
This stream is used for reading data from the files. Objects can be
created using thekeyword newandthere areseveral types ofconstructors
available.
Following constructo r takes a file name as a string to create an input
stream object to read the file −
Following constructor takes afileobject tocreate aninput stream object
toread thefile.First wecreate afileobject using File() method asfollows
−
File f=new File("C:/java/hello");
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158Once you have Input Stream object in hand, then there is a list of
helper methods which can be used to read to stream or to do other
operations on thestream.
Sr.No. Method &Description
1 public void close() throws IOException{}
This method closes thefileoutput stream. Release sany
system resources associated with thefile. Throws anIO
Exception.
2 protected void finalize()throws IOException {}
This method cleans up the connection to the file. Ensures
that the close method of this file output stream is called
when there are no more references tothisstream. Throws
anIOException.
3 public intread(int r)throws IOException{}
This method reads the specified byte of data from the
InputStream. Returns an int. Returns the next byte of data
and-1 will be returned if it'stheend of thefile.
4 public intread(byte[] r)throws IOException{}
This method reads r. length bytes from the input stream into
an array. Returns the total number of bytes read. If it is the
end of the file, -1 will bereturned.
5 public intavailable( )throws IOException{}
Gives thenumber ofbytes thatcanberead from thisfile
input stream. Returns anint.
11.14 SAMPLE QUESTIONS
Q1. What is stream? Differentiate between stream source and stream
destination.
Q2.Write a program for I/O operation using Buffered Input Stream and
Buffered Output Stream
Q3.Write a program using File Reader and Print Writer classes for file
handling.
Q4.Which class may be used for reading from console?InputS tream f=new FileInputStream(f);
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159Q5.Write a program to read the output of a file and display it on console.
Q7.What is Java Stream Explain in with example.
Q8.What is Serialization?
Q9. Explain File Reader class With Example.
Q10. Explain File Writer class With Example.
Q11. Explain File class With Example.
Q12. Explain Char Array Reader class Wit h Example.
Q13. Explain Char Array Writer class With Example.
Q12. Explain Byte Array Input Stream class With Example.
Q13. Explain Byte Array Output Stream class With Example.
UNIT SUMMARY : -
In this unit we first discussed about an array, which is a fixed -length
data structure that can contain multiple objects of the same type. An
element within an array can be accessed by its index. Indices begin at
0 and end at the length of the array.
Also we discuss about how Java goes to great lengths to help you deal
with error conditions. In this unit we have discussed how Java's
exception mechanism s give a structured way to perform a go -to from
the place where an error occurs to the code that knows how to handle
the error. In this unit we have discussed different causes of exception,
using try, catch, finally, throw and throws clauses in exception
handling. This unit deals with ways to handle error conditions in a
structured, methodical way. This unit discusses types of exceptions,
Throwable class hierarchy, and explains how to write own exception
subclasses.
Also we discuss about working of multith reading in Java. Also you
have learned what is the main thread and when it is created in a Java
program. Different states of threads are described in this unit. This unit
explained how threads are created using Thread class and Runnable
interface. It expla ined how thread priority is used to determine which
thread is to execute next. This unit explains concept of
synchronization, creating synchronous methods and inter thread
communication. It is also explained how object locks are used to
control access to s hared resources.
Also we discuss about various methods of I/O streams -binary,
character and object in Java. This unit briefs that input and output in
the Java language is organised around the concept of streams. All
input is done through subclasses of Inp utStream and all output is done
through subclasses of Output Stream. (Except for Random Access
File). We have covered how various streams can be combined together
to get the added functionality of standard input and stream input. Inmunotes.in
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160this unit you have als o learned the operations of reading from a file
and writing to a file. For this purpose objects of File Reader and File
Writer classes are used.
UNIT FURTHER READINGS : -
Core Java for Beginners by Sharanam Shah
Java: The Complete Reference , Oracle , Aut hor: Herbert Schildt
E.Balaguruswamy, Programming with Java, second edition, Tata
McGraw Hill publications,2000
Programming with java , Tata McGraw -Hill Education by
E.Balgurusamy
Web Refrences : -
www.w3school.com
www.tutorialspoint.com
www.javatpoint.com
www.programiz.com
munotes.in
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161Unit V
12
EVENT HANDLING
Unit Structure
12.0 Objectives
12.1 Introduction
12.2 Event Handling
12.2.1 Delegation Event Model
12.2.2 Events
12.2.3 Event classes and Event listener interfaces
12.2.4 Using delegation event model
12.2.5 Adapter classes and inner classes
12.3 Let us Sum Up
12.4 List of References
12.5 Chapter End Exercises
12.0 OBJECTIVES
This chapter would make you understa nd the following concepts:
Define Event Handling in Java
Describe Event Handling in Java
Explain Two Event Handling Mechanisms.
Illustrate the Delegation Event Model in Java
Describe Components of Event Handling
Explain steps to handle an event in java
12.1 INTRODUCTION
In this chapter we will learn Event handling which is fundamental
to Java programming because it is integral to the creation of applets and
other types of GUI -based programs. Change in the state of an object is
known as event. Event des cribes the change in state of source. Events are
generated as result of user interaction with the graphical user interface
components. Event Handling is the mechanism that controls the event and
decides what should happen if an event occurs. This mechanism has the
code which is known as event handler that is executed when an event
occurs.munotes.in
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16212.2 EVENT HANDLING
Event handling isprime toJava programming because it’sintegral
tothecreation ofapplets andother sorts ofGUI-based programs. Events
aresupported byavariety ofpackages, including java.util, java.awt, and
java.awt.event. Theprogram response isgenerated when theuser interacts
with aGUI-based program.
Two event handling mechanisms injava
1.Original Version ofJava (1.0)
2.Modern Versions ofJava, beginning with Java version 1.1
The way during which events arehandled changed significantly
between thefirstversion ofJava (1.0) andevery onesubsequent version of
Java, beginning with version 1.1. Although the1.0method ofevent
handling remains supported, it’snotrecommended forbrand spanking
newprograms.
Also, many ofthemethods thatsupport theold1.0event model are
deprecated. Themodern approach isthewaythatevents should behandled
byall-new programs.
12.2.1 Delegation Event Model in Java
The Delegation Event model is defined to handle events in GUI
programming languages. The GUI stands for Graphical User Interface,
where a user graphically/visually interacts with the system.
The GUI programming is inheren tly event -driven; whenever a user
initiates an activity such as a mouse activity, clicks, scrolling, etc., each is
known as an event that is mapped to a code to respond to functionality to
the user. This is known as event handling.
In this section, we wil l discuss event processing and how to
implement the delegation event model in Java. We will also discuss the
different components of an Event Model.
Advantage ofusing delegation event model
The advantage ofthis design isthat theappliance logic that
processes events iscleanly separated from theinterface logic that
generates those events. Aninterface element isinaposition to“delegate”
theprocessing ofanoccasion toaseparate piece ofcode. Inthedelegation
event model, listeners must register with asource soastoreceive an
occasional notification. This provides isacrucial benefit: notifications are
sent only tolisteners thatwant toreceive them. This isamore efficient
waytohandle events.
Event Processing in Java
Java support event processing since Java 1.0. It provides support
for AWT ( Abstract Window Toolkit), which is an API used to developmunotes.in
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163the Desktop application. In Java 1.0, the AWT was based on inheritance.
To catch and process GUI events for a program, it should hold subclass
GUI components and override action() or handleevent() methods. The
below image demonstrates the event processing.
But, the modern approach for event processing is bas ed on the
Delegation Model. It defines a standard and compatible mechanism to
generate and process events. In this model, a source generates an event
and forwards it to one or more listeners. The listener waits until it receives
an event. Once it receives the event, it is processed by the listener and
returns it. The UI elements are able to delegate the processing of an event
to a separate function.
The key advantage of the Delegation Event Model is that the
application logic is completely separated from t he interface logic.
In this model, the listener must be connected with a source to
receive the event notifications. Thus, the events will only be received by
the listeners who wish to receive them. So, this approach is more
convenient than the inheritance -based event model (in Java 1.0).
In the older model, an event was propagated up the containment
until a component was handled. This needed components to receive events
that were not processed, and it took lots of time. The Delegation Event
model overcame this issue.
Basically, an Event Model is based on the following three components:
Events
Events Sources
Events Listeners
12.2.2 Event
Anevent isanobject that describes aphase change during a
source. Itisoften generated asaconsequence ofanindividual interacting
with theweather during agraphical interface. Some activities thatcause
events tobegenerated arepressing abutton, entering apersonality viathemunotes.in
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164keyboard, selecting anitem during alist,andclicking themouse. Events
canalsooccur thataren’t directly caused byinteractions with aninterface.
Forexample, anoccasion could alsobegenerated when atimer expires, a
counter exceeds aworth, asoftware orhardware failure occurs, oran
operation iscompleted.
Changing the state of an object is known as an event. For example,
click on button, dragging mouse etc. The java.awt.event package provides
many event classes a nd Listener interfaces for event handling.
12.2.3 Java Event classes and Listener interfaces
Event Classes
The classes that represent events aeatthecore ofJava’s event
handling mechanism. AttherootoftheJava event class hierarchy isevent
object ,which isinjava.util .Itisthesuper class forallevents.
THE ACTION EVENT CLASS
Anactioneventis generated when abutton ispressed, alistitem is
double -clicked, oramenu item isselected. Itdefines four integer
constants that canbeused toidentify anymodi fiers associated with an
action event: ALT_MASK ,CTRL_MASK ,META_MASK ,andSHIFT
_MASK .There isalso aninteger constant, ACTION_ PERFORMED ,
which canbeused toidentify action events.
Event listeners
Alistener isanobject that’snotified when anoccasion occurs. It
hastwomajor requirements. First, itregistered with oneormore sources
toreceive notifications about specific sorts ofevents. Second, it
implements methods toreceive and process these notifications. The
methods thatreceive andprocess events aredefined ininterfaces found
injava.awt.event .
Event Classes Listener Interfaces
Actionevent Actionlistener
Mouseevent Mouselistener and
mousemotionlistener
Mousewheelevent Mousewheellistener
Keyevent Keylistener
Itemevent Itemlistener
Textevent Textlistener
Adjustmentevent Adjustmentlistener
Windowevent Windowlistener
Componentevent Componentlistener
Actionlistener
The class which processes the action event should implement this
interface. The object of that class must be registered with a
component.munotes.in
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165The object can be registered using the add action listener() method.
When the action event occurs, that object's action performed
method is invoked.
Interface methodsS.N.Method & Description
1 Void actionper formed (actionevente)
Invoked when an action occurs.
//program to calculate factorial of a number entered in the textfield
Import java.awt.*;
Import java.awt.event.*;
Public class action listenerexextends Frame implements action listener{
Label l1,l2;
Textfieldt1;
Button b1;
Actionlistenerex()
{
Super("Action Listerner Example");
Setsize(200,200);
Setvisible(true);
Setlayout(new flowlayout());
L1=new Label("Enter a Number");
T1=new textfield(10);
B1=new Button("Factorial");
L2=new Label();
Add(l1);
Add(t1);
Add(b1);
Add(l2);
B1.addactionlistener(this);
}
Public void actionperformed(actionevente)
{munotes.in
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166String s=t1.gettext();
Int n=Integer.parseint(s);
Int f=1;
For(int i=1;i<=n;i++)
F=f*i;
L2.settext("Factorial of "+s+" is " +f);
}
Public static void main(String[] args) {
New actionlistenerex();
}
}
OUTPUT:
Itemlistener
The class which processes the itemevent should implement this
interface.
The object of that class must be registered with a component.
The object can be registered using the additemlistener() method.
When the action event occurs, that object's item state changed
method is invoked.
Interface m ethodsS.N.Method & Description
1 Void itemstatechanged(itemevente)
Invoked when an item has been selected or deselected by the
user.
// program to change the background color of a frame according to
the selection in choice control
Import java.awt.*;
Import java.awt.event.*;munotes.in
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167Public class choiceexextends Frame implements itemlistener{
Choice color;
Choiceex()
{
Setsize(300,400);
Setvisible(true);
Setlayout(new flowlayout());
Color=new Choice();
Color.add("Red");
Color.add("Green");
Color.add("b lue");
Add(color);
Color.additemlistener(this);
}
Public void itemstatechanged(itemevente)
{
If(color.getselectedindex()==0)
System.out.println(color.getitemcount());
Else if(color.getselectedindex()==1)
Setbackground(Color.green);
Else if(color.getselecteditem().equalsignorecase("Blue"))
Setbackground(Color.blue);
}
Public static void main(String[] args) {
New choiceex();
}
}
OUTPUT:
munotes.in
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168Windowlistener
The class which processes the window event should implement
this interface.
The object of that class must be registered with a component.
The object can be registered using the addwindowlistener()
method.
Interface MethodsS.N.Method & Description
1 Void window activated (windowevente)
Invoked when the Window is set to be the active Window.
2 Void window closed (windowevente)
Invoked when a window has been closed as the result of calling
dispose on the window.
3 Void window closing (windowevente)
Invoked when the user attempts to close the window from the
window's system menu.
4 Void window deactivated (windowevente)
Invoked when a Window is no longer the active Window.
5 Void window deiconified (windowevente)
Invoked when a window is changed from a minimized to a
normal state.
6 Void windowiconified(windowevente)
Invoked when a window is changed from a normal to a
minimized state.
7 Void window opened (windowevente)
Invoked the first time a window is made vis ible.
// program to implement Window Listener methods
Import java.awt.*;
Import java.awt.event.*;
Public class windowex2 extends Frame implements windowlistener{
Windowex2()
{
Super("Window Listener");
Setsize(300,300);
Setvisible(true);
Addwindowlistener(this);munotes.in
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169}
Public static void main(String[] args) {
New windowex2();
}
@Override
Public void windowopened(windowevente) {
System.out.println("Opened");
}
@Override
Public void windowclosing(windowevente) {
Dispose();
}
@Override
Public void windowclosed(windowevente) {
System.out.println("Closed");
}
@Override
Public void windowiconified(windowevente) {
System.out.println("Iconified");
}
@Override
Public void windowdeiconified(windowevente) {
System.out.println("deiconified");
}
@Override
Public void windowactivated(windowevente) {
System.out.println("Activated");
}
@Override
Public void windowdeactivated(windowevente) {
System.o ut.println("Deactivated");
}
}munotes.in
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170OUTPUT:
12.2.4 Using delegation event model
Using the delegation event model is actually quite easy. Just follow
these two steps: 1. Implement the appropriate interface in the listener so
that it will receive the type of event desired. 2. Implement code to register
and unregister (if necessary) the list ener as a recipient for the event
notifications.
Keylistener
The class which processes the keyevent should implement this
interface. The object of that class must be registered with a
component.
The object can be registered using the add keylistener() m ethod.
Interface MethodsS.N.Method & Description
1 Void keypressed(keyevente)
Invoked when a key has been pressed.
2 Void keyreleased(keyevente)
Invoked when a key has been released.
3 Void keytyped(keyevente)
Invoked when a key has been typed.
//program to check whether the entered number is even or odd as
soon as you typed the number
Import java.awt.*;
Import java.awt.event.*;
Public class keylistenerexextends Frame implements keylistener{
Label l1,l2;munotes.in
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171Textfieldt1;
Keylistenerex()
{
Super ("Key Listener Example");
Setsize(200,200);
Setvisible(true);
Setlayout(new flowlayout());
L1=new Label("Enter a Number");
T1=new textfield(10);
L2=new Label();
Add(l1);
Add(t1);
Add(l2);
T1.addkeylistener(this);
}
Public void keytyped(keyevente)
{
}
Public void keypressed(keyevente)
{
}
Public void keyreleased(keyevente)
{
String s=t1.gettext();
Int n=Integer.parseint(s);
If(n%2==0)
L2.settext("Even");
Else
L2.settext("Odd");
}
Public static void main(String[] args) {
New keylistenerex();
}
}munotes.in
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172OUTPUT:
Mouse listener
The class which processes the mouse event should implement this
interface.
The object of that class must be registered with a component.
The object can be registered using the add mouse listener() method.
Interface MethodsS.N.Method & Description
1 Void mouse clicked (mouseevente)
Invoked when the mouse button has been clicked (pressed and
released) on a component.
2 Void mouseentered (mouseevente)
Invoked when the mouse enters a component.
3 Void mouseexited (mouseevente)
Invoked when the mouse exits a component.
4 Void mousepressed (mouseevente)
Invoked when a mouse button has been pressed on a
component.
5 Void mousereleased(mous eevente)
Invoked when a mouse button has been released on a
component.
//program to change background color of frame on every mouse event
Import java.awt.*;
Import java.awt.event.*;
Public class mouselistenerexextends Frame implements mouselistener{
Mouselistenerex(){
Super("Mouse Listener");munotes.in
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173Addmouselistener(this);
Setsize(300,300);
Setlayout(null);
Setvisible(true);
}
Public void mouseclicked(mouseevente) {
Setbackground(Color.red);
}
Public void mouseentered(mouseevente) {
Setbackground(Color.green);
}
Public void mouseexited(mouseevente) {
Setbackground(Color.blue);
}
Public void mousepressed(mouseevente) {
Setbackground(Color.yellow);
}
Public void mousereleased(mouseevente) {
Setbackground(Colo r.black);
}
Public static void main(String[] args) {
New mouselistenerex();
}
}
OUTPUT:
Mouse motion listener
The inter face mouse motion listener is used for receiving mouse
motion events on a component.
The class that process mouse motion events needs to implements
this interface.munotes.in
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174S.N.Method & Description
1 Void mousedragged(mouseevente)
Invoked when a mouse button is pressed on a component and
then dragged.
2 Void mousemoved(mouseevente)
Invoked when the mouse cursor has been moved onto a
component but no buttons have been pushed.
//program to implement Mouse Motion Listener
Import java.awt.*;
Import java.awt.even t.*;
Public class mouse motion listenerexextends Frame implements
mousemotionlistener{
Mousemotionlistenerex()
{
Super("Mouse Listener");
Addmousemotionlistener(this);
Setsize(300,300);
Setvisible(true);
}
Public void mousedragged(mouseevente)
{
System.out.println("mousedragged");
}
Public void mousemoved(mouseevente)
{
System.out.println("mousemoved");
}
Public static void main(String[] args) {
New mousemotionlistenerex();
}
}munotes.in
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175OUTPUT:
13.2.5 adapter classes and inner classes
Java adapter classes provide the default implementation of listener
interfaces. If you inherit the adapter class, you will not be forced to
provide the implementation of all the methods of listener interfaces. So it
saves code.
Adapter class Listener interface
WindowAdapter WindowListener
KeyAdapter KeyListener
MouseAdapter MouseListener
MouseMotionAdapter MouseMotionListener
FocusAdapter FocusListener
ComponentAdapter ComponentListener
ContainerAdapter ContainerListener
HierarchyBoundsAdapter HierarchyBoundsListener
Windowadapter Example
Import java.awt.*;
Import java.awt.event.*;
Public class adapterexample{
Frame f;
Adapterexample(){
F=new Frame("Window Adapter");
F.addwindowlistener(new windowadapter(){munotes.in
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176Public void windowclosing(wind owevente) {
F.dispose();
}
});
F.setsize(400,400);
F.setlayout(null);
F.setvisible(true);
}
Public static void main(String[] args) {
New adapterexample();
}
}
OUTPUT:
Inner class:
Theinner class isdefined inside thebody ofanother class (known
asanouter class). Theclass written within iscalled thenested class, and
theclass thatholds theinner class iscalled theouter class. Java inner class
canbedeclared private, public ,protected, orwith default access whereas
anouter class canhave only public ordefault access.
Weuseinner classes tologically group classes andinterfaces in
oneplace sothatitcanbemore readable andmaintainable. TheSyntax is
given below.
Class Outerclass
{
Class Innerclass
{
//code
}
}munotes.in
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177Types ofinner classes injava:
1.Nested Inner Class
2.Method Local Inner Class
3.Anonymous Inner Class
4.Static Nested Class
Nested inner class injava:
Aclass created within theclass andoutside themethod isknown
asNested Inner Class .Itcanaccess theprivate instance variable ofthe
outer class.
Example:
Package Demo;
Public class nestedinnerclass{
Class Inner {
Public void show() {
System.out.println("In a nested class method");
}
}
Public static void main(String[] args) {
Nestedinnerclass.Inner in = new nestedinnerclass().new Inner();
In.show();
}
}
Method local inner class injava:
Aclass created withinthemethod oftheenclosing class isknown
asMethod Local Inner Class. Since thelocal inner class isnotassociated
with Object, wecan’t useprivate, public, orprotected access modifiers
with it.Theonly allowed modifiers areabstract orfinal.
Example:
Package Demo;
Public class methodlocalinnerclass{
Void outermethod() {
System.out.println("Inside outermethod");
// Inner class is local to outermethod()
Class Inner {
Void innermethod() {
System.out.println("Inside innermethod");
}
}
Inner y = new Inner();munotes.in
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178Y.innermethod();
}
Public static void main(String[] args) {
Methodlocalinnerclassouter = new methodlocalinnerclass();
Outer.outermethod();
}
}
Anonymous inner class injava:
Aninner class declared without aclass name isknown as
ananonymous inner class. Itiscreated forimplementing aninterface or
extending class. Since ananonymous class hasnoname, itisnotpossible
todefine aconstructor forananonymous class. Itsname isdecided bythe
javacompiler.
Example:
Package Demo;
Abstract class Animal{
Abstract void dog();
}
Class anonymousinnerclass{
Public static void main(String args[]){
Animal p=new Animal(){
Void dog(){
System.out.println("Dog is an Animal.");
}
};
P.dog();
}
}
Static nested class:
Static nested classes arenottechnically inner classes. They arelike
static members oftheouter class. Astatic nested class isthesame asany
other top-level class and isnested foronly packaging convenience.
Because thisisstatic innature sothistype ofinner class doesn’t share any
special kind ofrelationship with aninstance oftheouter class. Astatic
nested class cannot access non-static members oftheouter class.
Example:
Package Demo;
Public class staticnestedclass{
Static class Nested_Demo {
Public void my_method() {munotes.in
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179System.out.println("This is my nested class");
}
}
Public static void main(String args[]) {
Staticnestedclass.Nested_Demo nested = new
staticnestedclass.Nest ed_Demo();
Nested.my_method();
}
}
12.3 LET US SUM UP
Changing the state of an object is known as an event. For example,
click on button, dragging mouse etc. The java.awt.event package provides
many event classes and Listener interfaces for event handling.
12.4 LIST OF REFERENCES
1. Core Java 8 for Beginn ers, Vaishali Shah, Sharnam Shah SPD 1st 2015
2. Java: The Complete Reference Herbert Schildt McGraw Hill 9th 2014
12.5 CHAPTER END EXERCISES
1.Explain Delegation Event Model in Java
2.Explain keyadapter class defined in Java with code segment.
3.Explain mouse adapter class defined in Java with code segment.
4.Develop a frame that has three radio buttons Red, Green, Blue. On
Click of any one of them background color of the frame should change
accordingly.
5.Explain the following interfaces:
i) Key Listener ii) Mouse Listen er
6.What is the use of adapter class in Java? Explain any one of the
adapter classes defined in Java.
7.Define Event Handling in Java.
8.Describe Event Handling in Java.
9.Explain Two Event Handling Mechanisms.
10.Illustrate the Delegation Event Model in Java.
11.Describe Components of Event Handling.
12.Explain steps to handle an event in java.
munotes.in
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180 13
ABSTRACT WINDOW TOOLKIT
Unit Structure
13.0 Objectives
13.1 Introduction
13.2 Abstract Window Toolkit
13.2.1 Window Fundamentals,
13.2.2 Component, Container, Panel, Window, Frame, Canvas.
13.2.3 Components – Labels, Buttons, Check Boxes, Radio Buttons,
Choice Menus, Text Fields, Text, Scrolling List, Scrollbars,
Panels, Frames
13.3 Programs
13.4 Let us Sum Up
13.5 List of References
13.6 Chapter End Exercises
13.0 OBJECTIVES
This chapter would make you understand the following concepts:
Define Abstract Windows Toolkit (AWT) in Java
Describe Why AWT is platform dependent
Explain Features of AWT in Java
Illustrate AWT Hierarchy
Define AWT Component
13.1 INTRODUCTION
In this chapter we will learn AWT. To develop the GUI based
applications we have to use AWT. AWT stands for Abstract Windowing
Toolkit. The set of classes and interfaces which are required to develop
GUI components together are called “Toolkit”. The GUI components will
be used to design GUI programs. Writing a program to display the created
GUI components on the windows is called “windowing”. To display the
components on the windows we need to take the support of graphics
available in the operating system. For a developer, there is no direct
interaction with the graphics and hence graphics is “Abstract” to the
developer. Every GUI component will have a corresponding “PEER” class
which is responsible to interact with the graphics of the operating system.
munotes.in
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181 13.2 ABSTRACT WINDOW TOOLKIT
The Java AWT creates components by calling the subroutines of
native platforms. Hence, an AWT GUI application will have the look and
feel of Windows OS while running on Windows and Mac OS look and
feel when running on Mac and so on. This explains the platform
dependency of Abstract Window Toolkit applications.
Due to its platform -dependence and a kind of heavyweight nature of
its components, it is rarely used in Java applications these days.
Besides, there are also newer framew orks like Swing which are light -
weight and platform -independent.
Java AWT (Abstract Window Toolkit) is an API to develop GUI or
window -based applications in java.
Java AWT components are platform -dependent i.e. Components are
displayed according to the vie w of operating system. AWT is
heavyweight i.e. Its components are using the resources of OS.
The java.awt package provides classes for AWT API such as textfield,
Label, textarea, radiobutton, checkbox, Choice, List etc.
13.2.1 Window Fundamentals
The AWT defines windows according to a class hierarchy that adds
functionality and specificity with each level. The two most common
windows are those derived from Panel, which is used by applets, and those
derived from Frame, which creates a standard application window.
13.2.2 Components, Container, Panel, Window, Frame, Canvas
The hierarchy of Java AWT classes are given below :
munotes.in
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182 As shown in the above figure the root AWT component
‘Component’ extends from the ‘Object’ class. The component class is the
parent of the other components including Label, Button, List, Checkbox,
Choice, Container, etc.
A container is further divided into panels and windows. An Applet
class derives from Panel while Frame and Dialog derive fro m the Window
component.
Components are as follows:
Container
The Container is a component in AWT that can contain another
components like buttons, textfields, labels etc. The classes that extends
Container class are known as container such as Frame, Dial og and Panel.
Window
The window is the container that have no borders and menu bars.
You must use frame, dialog or another window for creating a window.
Panel
The Panel is the container that doesn't contain title bar and menu
bars. It can have other comp onents like button, textfield etc.
Frame
The Frame is the container that contain title bar and can have menu
bars. It can have other components like button, textfield etc.
Canvas
The Canvas control represents a blank rectangular area where the
applicatio n can draw or trap input events from the user. It inherits the
Component class.
Component Class
Method Description
Public void add(Component c) Inserts a component on this component.
Public void setsize (int width,
int height) Sets the size (width and height) of the
component.
Public void setlayout (layout
manager m) Defines the layout manager for the
component.
Public void setvisible (boolean
status) Changes the visibility of the component,
by default false.
Creating Frames
To create simple awt example, you need a frame. There are two ways
to create a frame in AWT.
o By extending Frame class (inheritance)
o By creating the object of Frame class (association) munotes.in
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183 Creating Frame by Association
The given example creates instance of em pty Frame class with
“MYFRAME” as title.
importjava.awt.*;
class frame1 {
fram e1(){
frame f=new Frame(“MYFRAME”);
f.setsize(300,300); //frame size 300 width and 300 height
f.setvisible(true); //now frame will be visible, by default not
visible
}
public static void main( string args[]){
frame1 f=new frame1();
}}
OUTPUT:
Creating Frame by Inheritance
The given example creates instance of empty Frame class with
“MYFRAME” as title.
import java.awt.*;
class first extends frame {
first(){
super(“MYFRAME”); //frame title
setsize (300,300);//frame size 300 width and 300 height
setvisible (true);//now frame will be visible, by default not visible
}
public static void main( string args[]){
first f=new first();
}}
munotes.in
Page 184
184 OUTPUT:
13.2.3 Components – Labels, Buttons, Check Boxes, Radio Buttons,
Choice Menus, Text Fields, Text, Scrolling List, Scrollbars, Pa nels,
Frames
Label
The object of Label class is a component for placing text in a
container. It is used to display a single line of read only text. The text can
be changed by an application but a user cannot edit it directly.
Constructors Description
label() Constructs an empty label.
label(String text) Constructs a new label with the specified
string of text, left justified.
label(string text, int
alignment) Constructs a new label that presents the
specified string of text with the specified
alignment.
Methods Description
string gettext() Gets the text of this label.
void settext(String text) Sets the text for this label to the specified
text.
int getalignment() Gets the current alignment of this label.
void setalignment
(intalignment) Sets the alignment for this label to the
specified alignment.
//creates two labels
import java.awt.*;
public class labelex extends frame {
label l1,l2;
labelex()
{
super(" label example ");
setsize(300,300); munotes.in
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185 setvisible(true);
setlayout(new flowlayout());
L1=new label(" first label ");
L2=new label("second label");
add(l1);
add(l2);
}
public static void main( string[] args) {
new labelex();
}
}
OUTPUT:
Button
The button class is used to create a labeled button that has platform
independent implementation. The application result in some action when
the button is pushed.
Constructors Description
button() Constructs a button with an empty string for its
label.
button(string text) Constructs a new button with specified label.
Methods Description
void setlabel(string label) Sets the button's label to be the
specified string.
string getlabel() Gets the label of this button
void add action listener (action
listener l) Adds the specified action listener to
receive action events from this button.
void remove action listener
(action listener l) Removes the specified action listener so
that it no lo nger receives action events
from this button.
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186 //creating button
import java.awt.*;
public class buttonex extends frame {
button b1,b2;
buttonex()
{
super("button example");
setsize(300,300);
setvisible(true);
setlayout(new flowlayout());
b1=new button("first button");
b2=new button("second button");
add(b1);
add(b2);
}
public static void main( string[] args) {
new buttonex();
}
}
OUTPUT
Text field
The object of a text field class is a text component that allows the
editing of a single line text. It inherits text component class.
Constructors Description
text field () Constructs a new text field.
text field (int columns) Constructs a new empty text field with the
specified number of columns.
text field (string text) Constructs a new text field initialized with the
specified text.
text field (string text, int
columns) Constructs a new text field initialized with the
specified text to be displayed, and wide enough
to hold the specified number of columns.
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187 Methods Description
void settext( string t) Sets the text that is presented by this text
component to be the specified text.
string gettext() Gets the text of the text field .
void setechochar
(char c) Sets the echo character for this text field.
char getechochar() Gets the character that is to be used for echoing.
void addactionlistener
(actionlistener l) Adds the specified action listener to receive
action events from this text field.
int getcolumns() Gets the number of columns in this text field.
void setcolumns
(intcolumns) Sets the number of columns in this text field.
//creating textfield
import java.awt.*;
public class textfieldex extends frame {
textfield t1,t2;
textfieldex()
{
super("button example ");
setsize(300,300);
setvisible(true);
setlayout(new flowlayout());
t1=new textfield(10); // creates empty textfield
t2=new textfield("Hello", 20);
add(t1);
add(t2);
}
public static void main( string[] args) {
new textfieldex();
} }
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188 OUTPUT
Text area
The object of a text area class is a multi line region that displays
text. It allows the editing of multiple line text. It inherits text component
class.
Field
Following are the fields for java.awt.text area class:
Static int SCROLLBARS_BOTH -- Create and display both
vertical and horizontal scrollbars.
Static int SCROLLBARS_HORIZONTAL_ONLY -- Create
and display horizontal scrollbar only.
Static int SCROLLBARS_NONE -- Do not create or display any
scrollbars for the text area.
Static int SCROL LBARS_VERTICAL_ONLY -- Create and
display vertical scrollbar only.
Constructors Description
textarea() Constructs a new text area with the
empty string as text.
textarea (int rows, int columns) Constructs a new text area with the
specified number of rows and columns
and the empty string as text.
textfield (string text) Constructs a new text area initialized
with the specified text.
textfield (string text, int rows,
int columns) Constructs a new text area with the
specified text, and with the specified
number of rows and columns.
textarea (string text, int rows,
int columns, int scrollbars) Constructs a new text area with the
specified text, and with the rows,
columns, and scroll bar visibility as
specified.
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189 Methods Description
void settext( string t) Sets the text that is presented by this
text component to be the specified
text.
string gettext() Gets the text of the textarea.
int getcolumns() Gets the number of columns in this
text area.
void setcolumns(int columns) Sets the number of columns in this
text area.
int getrows() Gets the number of rows in this text
area.
void setrows(int rows) Sets the number of rows in this text
area.
void append( string str) Appends the given text to the text
area's current text.
void insert( string str, int pos) Inserts the specified text at the
specified position in this text area.
//creating textarea
import java.awt.*;
public class textareaex extends frame {
textarea t1,t2,t3;
textareaex()
{
super("textfield example");
setsize(300,300);
setvisible(true);
setlayout(new flowlayout());
t1=new textarea(5,10); // creates empty textfield
t2=new textarea("Hello",10, 10 );
t3=new textarea(" i am a student of VSIT
college",5,10,textarea.SCROLLBARS_HORIZONTAL_ONLY);
add(t1);
add(t2);
add(t3);
} munotes.in
Page 190
190 public static void main( string[] args) {
new textareaex();
}
}
OUTPUT:
Checkbox
The Checkbox class is used to create a checkbox. It is used to turn
an option on (true) or off (false). Clicking on a Checkbox changes its state
from "on" to "off" or from "off" to "on".
Constructor Description
checkbox() Creates a check box wit h an empty string
for its label.
checkbox( string label) Creates a check box with the specified
label.
checkbox(String label, boolean
state) Creates a check box with the specified
label and sets the specified state.
checkbox(String label, boolean
state, check boxgroup group) Constructs a Checkbox with the
specified label, set to the specified state,
and in the specified check box group.
checkbox( string label,
checkbox group group,
boolean state) Creates a check box wi th the specified
label, in the specified check box group,
and set to the specified state.
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191 Methods Description
void setlabel (string label) Sets this check box's label to be the string
argument.
string getlabel() Gets the label of this check box.
void setstate (boolean state) Sets the state of this check box to the
specified state.
boolean getstate() Determines whether this check box is in
the on or off state.
void additemlistener
(itemlistener l) Adds the specified item listener to receive
item events from this check box.
//creating Checkbox
import java.awt.*;
public class checkboxex extends frame {
label l1;
checkbox c1,c2,c3;
checkboxex()
{
super("checkbox example ");
setsize(300,300 );
setvisible(true);
setlayout(new flowlayout());
l1=new label("select your hobbies");
c1=new checkbox("singing",true);
c2=new checkbox("dancing",false);
c3=new checkbox("reading",true);
add(l1); add(c1); add(c2); add(c3);
}
public static void main( string[] args) {
new checkboxex();
} }
OUTPUT:
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192 Checkbox group
The object of checkbox group class is used to group together a set
of Checkbox. At a time only one check box button is allowed to be in "on"
state and remaining check box button in "off" state. It inherits the object
class.
Constructor Description
Checkbox group() () Creates a new instance of checkbox group.
Methods Description
checkbox getselected
checkbox() Gets the current choice from this check box
group.
void setselected
checkbox (checkbox
box) Sets the currently selected check box in this
group to be the specified check box.
//creating radiobuttons
import java.awt.*;
public class radiobuttonex extends Frame {
label l1;
checkbox c1,c2,c3;
checkboxgroup cg;
radiobuttonex()
{
super("ra diobutton example");
setsize(300,300);
setvisible(true);
setlayout(new flowlayout());
cg=new checkboxgroup();
l1=new label(" select your color ");
c1=new checkbox("red", cg,true);
c2=new checkbox("green",cg,false);
c3=new checkbox("blue",cg,false);
add(l1);
add(c1);
add(c2);
add(c3);
}
public static void main(string[] args) {
new radiobuttonex();
}
}
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193 OUTPUT:
Choice
The object of Choice class is used to show popup menu of choices.
Choice selected by user is shown on the top of a menu. It inherits
Component class.
Constructor Description
Choice() Creates a new choice menu.
Methods Description
void add(string item) Adds an item to this Choice menu.
void additemlistener
(itemlistener l) Adds the specified item listener to receive
item events from this Choice menu.
string getitem (int index) Gets the string at the specified index in this
Choice menu.
int getitemcount() Returns the number of items in this Choice
menu.
int getselectedindex() Returns the index of the currently selected
item.
string getselecteditem() Gets a representation of the current choice
as a string.
void insert(string item, int
index) Inserts the item into this choice at the
specified position.
void remove(int position) Removes an item from the choice menu at
the specified position.
void remove(string item) Removes the first occurrence of item from
the Choice menu.
void removeall() Removes all items from the choice menu.
//creating dropdown list
import java.awt.*;
public class choiceex extends frame {
label l1;
choice c;
choiceex()
{
super("choice example"); munotes.in
Page 194
194 setsize(300,300);
setvisible(true);
setlayout(new flowlayout());
l1=new label("select color");
c=new choice();
c.add("red");
c.add("green");
c.add("blue");
add(l1);
add(c);
}
public static void main(string[] args) {
new choiceex();
} }
OUTPUT:
List
The object of List class represents a list of text items. By the help
of list, user can choose either one item or multiple items. It inherits
Component class.
Constructor Description
list() Creates a new scrolling list.
list(int rows) Creates a new scrolling list initialized
with the specified number of visible lines.
list(int rows, boolean
multiplemode) Creates a new scrolling list initialized to
display the specified number of rows.
Methods Description
void add(string item) Adds the specified item to the end of
scrolling list.
void add(string item, int
index) Adds the specified item to the the scrolling
list at the position indicated by the index.
int getitemcount() Gets the number of items in the list.
string getitem(int index) Gets the item associated with the specified
index. munotes.in
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195 string[] getitems() Gets the items in the list.
int getselectedindex() Gets the index of the selected item on the
list,
int[] getselectedindexes() Gets the selected indexes on the list.
string getselecteditem() Gets the selected item on this scrolling list.
string[] getselecteditems() Gets the selected items on this scrolling
list.
void remove(int position) Removes the item at the specified positi on
from this scrolling list.
void remove(string item) Removes the first occurrence of an item
from the list.
void removeall() Removes all items from this list.
// creating scrolling list
import java.awt.*;
public class listex extends frame {
label l1,l 2;
list course,subject;
listex()
{
super("list example");
setsize(300,300);
setvisible(true);
setlayout(new flowlayout());
l1=new label("select course");
l2=new label("select subjects");
course=new list(5);
subject=new list(5,true); //multi select list
course.add("fyit");
course.add("syit");
course.add("tyit");
course.add("mscit part 1");
course.add("mscit part 2");
course.add("fybms");
subject.add("dm"); //0
subject.add("cj"); //1
subject.add("ies"); //2
subject.add("am");
subject.add("ma"); munotes.in
Page 196
196 subject.add("ip");
subject.add("dbms");
subject.add("python",2);
add(l1); add(course); add(l2);
add(subject);
}
public static void main(string[] args) {
new listex();
} }
OUTPUT
13.3 PROGRAMS
a. Create an AWT application to create a Frame with a Button named
cube, a Label and a Text Field. Click of the button should display
cube of that number in the Label.
import java.awt.*;
import java.awt.event.*;
public class numex extends frame implements actionlistener{
label l1,l2;
textfield t1;
button b1;
numex()
{
super("cube ");
setlayout(new flowlayout());
l1=new label("enter a number: -");
l2=new label();
t1=new textfield();
b1=new button("cube");
b1.addactionlistener(this); munotes.in
Page 197
197 add(l1);
add(t1);
add(b1);
add(l2);
setsize(300,300);
setvisible(true);
}
public static void main(string[] args) {
new numex();
}
public void actionperformed(actionevent e) {
int n=integer.parseint(t1.gettext());
l2.settext((n*n*n)+"");
}
}
b. Develop a frame that has three radio buttons Red, Green, Blue. On
Click of any one of them background color of th e frame should
change accordingly.
import java.awt.*; import java.awt.event.*;
public class colorclass extends frame implements itemlistener
{
checkbox r1,r2,r3;
checkboxgroup chg;
colorclass( )
{
setlayout(new flowlayout());
chg=new checkboxgroup();
r1=new checkbox("red",chg,true);
r2=new checkbox("green",chg,false);
r3=new checkbox("blue",chg,false);
add(r1); add(r2); add(r3);
r1.additemlistener(this); r2.additemlistener(this); r3.additemlisten er(this);
setbackground(color.red);
setsize(500,500);
setvisible(true);
}
public static void main(string args[])
{
new colorclass();
} munotes.in
Page 198
198 @override public void item state changed( item event e)
{
if(e.getsource()==r1)
setbackground(color.red);
else if(e.getsource()==r2)
setbackground(color.green);
else setbackground(color.blue);
}
}
c. Write a program to demonstrate the use of Canvas.
Canvas control represents a rectangular area where application can
draw something or can receive inputs created by user.
import java.awt.*;
public class canvasexample
{
public canvasexample()
{
frame f= new frame("canvas example");
f.add(new mycanvas());
f.setlayout(null);
f.setsize(400, 400);
f.setvisible(true);
}
public static void main(strin g args[])
{
new canvasexample();
}
}
class mycanvas extends canvas
{
public mycanvas()
{
setbackground (color.gray);
setsize(300, 200);
}
public void paint(graphics g)
{
g.setcolor (color.red);
g.filloval(75, 75, 150, 75);
}
} munotes.in
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199 13.4 LET US SUM UP
The java.awt.event package provides many event classes and
Listener interfaces for event handling. The java.awt package provides a
great deal of functionality and flexibility. With the help of this notes, you
should get an excellent grasp of the java.awt, java.awt.event.
13.5 LIST OF REFERENCES
1. Core Java 8 for Beginners, Vaishali Shah, Sharnam Shah SPD 1st 2015
2. Java: The Complete Reference Herbert Schildt McGraw Hill 9th 2014
13.6 CHAPTER END EXERCISES
1. Define Component, Panel, Canvas, Window and Frame.
2. Write a short note on checkbox and checkbox group class.
3. List various layouts in AWT and Explain Border Layout with
example.
4. Write the constructors and methods of checkbox class. Also explain
the use of checkbox group class.
5. Explain any two over loaded constructors and three methods of Label
class.
6. Write a short note on Choice and List class.
7. Write a program to display “Good Morning” in blue with font size 20
and font name Times New Roman in bold and italic.
8. Develop a frame that has three radio bu ttons Red, Green, Blue. On
Click of any one of them background color of the frame should change
accordingly.
9. Write aprogram to Design a AWT program to print the factorial for an
input value.
10. Design a Registration Form.
11. Explain the hierarchy of AWT componen ts.
12. Explain any two overloaded constructors and three methods of class
Text Field.
13. What is the use of adapter class in Java? Explain any one of the
adapter classes defined in Java.
14. Create an AWT application to create a Frame with a Button named
cube, a Label and a Text Field. Click of the button should display cube
of that number in the Label.
15. Explain Choice class along with constructors in detail.
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Page 200
20014
LAYOUTS
Unit Structure
14.0 Objectives
14.1 Introduction
14.2 Layouts
14.2.1 Flow Layout
14.2.2 Grid Layout
14.2.3 Border Layout
14.2.4 Card Layout
14.3 Let us Sum Up
14.4 List of References
14.5Unit End Exercises
14.0 OBJECTIVES
This chapter would make you understand the following concepts:
Flow Layout
Grid Layout
Border Layout
Card Layout
Programs using layouts
14.1 INTRODUCTION
In this unit we will learn different layouts .Layouts defines how UI
elements should be organized on the screen and provide a final look and
feel to the GUI.The layout is used to enhance the look and feel of the
application. To arrange t he components in a container, the various layout
classes can be used such as Flow layout and Border Layout. These layouts
use relative positioning to place the components on the container, which
means the components automatically adjust their position acco rding to the
frame size.
14.2 LAYOUT MANAGERS
The layout managers are used to arrange components in a
particular manner. Layout manager is an interface that is implemented by
all the classes of layout managers. There are following classes that
represents the layout managers:munotes.in
Page 201
2011.Java.awt.flowlayout
2.Java.a wt.gridlayout
3.Java.awt.borderlayout
4.Java.awt.cardlayout
14.2.1 Flow Layout
The flowlayout is used to arrange the components in a line, one
after another (in a flow). It is the default layout of applet or panel.
Fields of flowlayout class
Public static final int LEFT
Public static final int RIGHT
Public static final int CENTER
Public static final int LEADING
Public static final int TRAILING
Constructors
Flowlayout() Creates a flow layout with centered
alignment and a default 5 unit
horizo ntal and vertical gap.
Flowlayout(int align) Creates a flow layout with the given
alignment and a default 5 unit
horizontal and vertical gap.
Flowlayout(int align, int hgap, int
vgap)Creates a flow layout with the given
alignment and the given horizontal
and vertical gap.
Example
Import java.awt.*;
Public class flowlayoutex extends Frame{
Button b1,b2,b3,b4,b5;
Flowlayoutex(){
B1=new Button("1");
B2=new Button("2");
B3=new Button("3");
B4=new Button("4");
B5=new Button("5");
Add(b1);add(b2);add(b3);add(b4);add(b5);
Setlayout(new flowlayout(flowlayout.RIGHT));
//setting flow layout of right alignmentmunotes.in
Page 202
202Setsize(300,300);
Setvisible(true);
}
Public static void main(String[] args) {
New flowlayoutex();
}
}
OUTPUT:
14.2.2 Grid Layout
The gridlayout is used to arrange the components in rectangular
grid. One com ponent is displayed in each rectangle.
Constructor
Gridlayout() Creates a grid layout with one column
per component in a row.
Gridlayout(int hgap, int vgap) Creates a grid layout with the given
rows and columns but no gaps
between the components.
Gridlayout(int rows, int
columns, int hgap, int vgap)Creates a grid layout with the given
rows and columns alongwith given
horizontal and vertical gaps.
// Example
Import java.awt.*;
Import java.awt.event.*;
Public class gridlayoutex extends Frame {
Label lbname,lbpass;
Textfield txtname,txtpass;
Button btnlogin,btncancel;
Gridlayoutex()
{munotes.in
Page 203
203Super("Grid Layout");
Setsize(300,400);
Setvisible(true);
Setlayout(new gridlayout(3,2));
Lbname=new Label("Username");
Lbpass=new Label("Password");
Txtname=new textfield(20);
Txtpass=new textfield(20);
Txtpass.setechochar('*');
Btnlogin=new Button("Login");
Btncancel=new Button("Cancel");
Add(lbname);
Add(txtname);
Add(lbpass);
Add(txtpass);
Add(btnlogin);
Add(btncancel);
Addwindowlistener(new windowadapter(){
Public void windowclosing(windowevent e)
{
Dispose();
}
});
}
Public static void main(String[] args) {
New gridlayoutex();
}
}
OUTPUT:
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Page 204
20414.2.3 Border Layout
The borderlayout is used to arrange the components in five
regions: north, south, east, west and center. Each region (area) may
contain one component only. It is the default layout of frame or window.
The borderlayout provides five constants for each regio n:
Public static final int NORTH
Public static final int SOUTH
Public static final int EAST
Public static final int WEST
Public static final int CENTER
Constructor
Borderlayout() Creates a border layout but with no gaps
between the components.
Jborderlayout(int hgap, int
vgap)Creates a border layout with the given
horizontal and vertical gaps between the
components.
Example
Import java.awt.*;
Public class borderlayoutex extends Frame {
Button b1,b2,b3,b4,b5;
Borderlayoutex(){
Super("Border Layout");
Setsize(500,500);
Setvisible(true);
B1=new Button("EAST");
B2=new Button("WEST");
B3=new Button("NORTH");
B4=new Button("SOUTH");
B5=new Button("CENTRE");
Add(b1,borderlayout.EAST);
Add(b2,borderlayout.WEST);
Add(b3,borderlayout.NO RTH);
Add(b4,borderlayout.SOUTH);
Add(b5,borderlayout.CENTER);
}
Public static void main(String[] args) {
New borderlayoutex();
}}munotes.in
Page 205
205OUTPUT:
14.2.4Card Layout
The cardlayout class manages the components in such a manner
that only one component is visible at a time. It treats each component as a
card that is why it is known as cardlayout.
Constructor
Cardlayout() Creates a card layout with zero horizontal
and v ertical gap.
Cardlayout(int hgap, int
vgap)Creates a card layout with the given
horizontal and vertical gap.
Method Description
Public void next(Container
parent)Is used to flip to the next card of the
given container.
Public void previous(Container
parent)Is used to flip to the previous card of
the given container.
Public void first(Container
parent)Is used to flip to the first card of the
given container.
Public void last(Container
parent)Is used to flip to the last card of the
given container.
Public void show(Container
parent,String name)Is used to flip to the specified card
with the given name.munotes.in
Page 206
206// Example
Import java.awt.*;
Import java.awt.event.*;
Public class cardlayoutex extends Frame implements actionlistener {
Button b1,b2,b3;
Cardlayout c;
Panel p;
Cardlayoutex()
{
Super("Card Layout");
Setsize(300,300);
Setvisible(true);
P=new Panel();
B1=new Button("First");
B2=new Button("Second" );
B3=new Button("Third");
C=new cardlayout(40,30);
P.setlayout(c);
P.add("a",b1);
P.add("b",b2);
P.add("c",b3);
B1.addactionlistener(this);
B2.addactionlistener(this);
B3.addactionlistener(this);
Add(p);
}
Public void actionperformed(actionevent e)
{
C.next(p);
}
Public static void main(String[] args) {
New cardlayoutex();
}
}munotes.in
Page 207
207OUTPUT:
14.3LET US SUM UP
LayoutManager is an interface that is implemented by all the classes
of layout managers. The Layout Managers are used to arrange components
in a particular manner. Layout Manager is an interface that is implemented
by all the classes of layout managers.
The default layout of frame is border layout. It is used to arrange
component in five regions east,west,center,north and south
Constructor
1.BorderLayout()
2.BorderLayout(int horz,int vert)
14.4 LIST OF REFERENCES
1. Core Java 8 for Beginners, Vaishali Shah, Sharnam Shah SPD 1st 2015
2. Java: The Complete Reference Herbert Schildt McGraw Hill 9th 2014munotes.in
Page 208
S.Y. B.Sc. (IT)
SEMESTER - IV(CBCS)
CORE JAV A
SUBJECT CODE :USIT401
munotes.in
Page 209
© UNIVERSITY OF MUMBAI
ipin Enterprises
Tantia Jogani Industrial Estate, Unit No. 2,
Ground Floor, Sitaram Mill Compound,
J.R. Boricha Marg, Mumbai - 400 011Published by : Director
Institute of Distance and Open Learning ,
University of Mumbai,Vidyanagari, Mumbai -400 098.December 2021, Print - I Programme Co-ordinator : Shri Mandar Bhanushe
Head, Faculty of Science and Technology
IDOL, University of Mumbai, Mumbai
Course Co-ordinator :Ms. Gouri Sawant
Asst. Professor, B.Sc. IT,
IDOL, University of Mumbai, Mumbai
Editor :Dr Asif Rampurawala
Asst. Professor,
Vidyalankar college of Information Technology,
Wadala, Mumbai
Course Writers :Ms. Pragati Ubale
Asst. Professor,
Satish Pradhan Dnyanasadhana College, Thane
:Mr Vinayak Pujari
Asst. Professor,
I.C.S. College of Arts, Commerce and
Science, khed, Ratnagiri
:Mr Tejas R. Jadhav
Asst. Professor,
VPM’s B.N.Bandodkar College of Science
(Autonomous ), Thane.
:Ms Pallavi Tawde
Asst. Professor,
Vidyalankar college of Information Technology,
Wadala, Mumbai
DTP Composed : Mumbai University Press
Printed by Vidyanagari, Santacruz (E), Mumbai - 400 098Prof. Suhas Pednekar
Vice-Chancellor,
University of Mumbai
Prof. Ravindra D. Kulkarni Prof. Prakash Mahanwar
Pro Vice-Chancellor, Director,
University of Mumbai IDOL, University of Mumbai
munotes.in
Page 210
CONTENTS
Unit No. Title Page No.
Unit - I
1. Introduction To Java Programming 01
2. Data Types 28
Unit - II
3. Control Statements 45
4. Classes 64
5. Constructors 78
Unit - III
6. Inheritance 90
7. Packages 105
Unit - IV
8. Enumerations, Arrays 111
9. Multithreading 121
10. Exceptions 131
11. Byte Streams 140
Unit - V
12. Event Handling 161
13. Abstract Window Toolkit 180
14. Layouts 200
munotes.in
Page 211
20814.5 CHAPTER END EXERCISES
1.Write a program to display a content using Flow Layout.
2.What is the role of layout manager? What is the default layout of
Frame? Explain its working.
3.Write a program to display a registration page using Grid Layout.
4.Write a program to display a home page using Border Layout.
5.Write a program to display a about page using Card Layout.
munotes.in