Java Book

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Java Programming 1

Version July 2000 Second Impression

The Team Production / Series Supervision Jambu Krishnamurthy Vice President – Product Development The Head Sridhar Subramaniam Head – Training Solutions Technical Writers Thiru Murugan .H Uma .S Ajay Balaji Review Jambu Krishnamurthy Sridhar Subramaniam Production/Design Vijay. V Editor Nurjehan Dhanani

Copyright  1999, Comp-U-Learn Inc. All Rights Reserved

No Part of this Book may be reproduced in any form by any means, stored in a retrieval system, or transmitted by any mode, electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher. Exceptions are made to the program listings, which can be typed, stored in a Computer System and executed. No patent liability is assumed with respect to the use of the information contained herein. Although every precaution has been taken in the preparation of this book, the publisher assumes no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein.

All Trade Marks Acknowledged

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Before We Begin 6RPHERG\ VDLG WKDW RQH·V JRDO LV WR HYROYH DQG ILQG JUHDWHU KHLJKWV
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Objectives of this Book 7KLVERRNLVLQWHQGHGWRJLYHSUHOLPLQDU\DQGLQWHUPHGLDWHH[SRVXUHRQ-DYD /DQJXDJH $W WKH HQG RI WKLV PRGXOH \RX VKRXOG EH DEOH WR ZULWH D -DYD $SSOLFDWLRQ RU -DYD $SSOHWV FRPIRUWDEO\ FRPSLOH LW DQG H[HFXWH LW
Conventions Used in this Book ♦ Each session is divided into 12 topics. It is called the Twelve Point Program (12pp). In every session, these points are distinctly shown in an underlined bigger font. ♦ Subheadings appear in bold without underlining. ♦ Note is shown inside a box. It is information which is necessary to understand the subject discussed but does not come as a part of the text flow. ♦ Summary is at the end of each session, shown in a special table, italicized. ♦ Each session ends with a ‘Going Over It Again’. This helps the student in recapitulating the session contents. ♦ Figure numbers and descriptions are given below each picture, diagram or screen for proper navigation.

iii

Session 1

Java-An Introduction

On Completion of this Session We will be able to understand...

) ) )

Basic concepts in Java

) ) )

About Java Application

Java as an OOP language Tools in Java About Java Applet Features of Java

In This Session...

Introduction to Java

History of Java

Features in Java

Java and Internet

Java-An OOP Language

C++ vs Java

Java Tools

Application Programming

Creating an Application

Applet Programming

Creating an Applet

Overview of Java

JAVA-An Introduction

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Comp-U-Learn

3

Java Programming I

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4

Comp-U-Learn

JAVA-An Introduction

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Comp-U-Learn

5

Java Programming I

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6

Encapsulation Inheritance Polymorphism Interfaces

Comp-U-Learn

JAVA-An Introduction

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C++ vs. Java $OWKRXJK-DYDLVREMHFWRULHQWHGWKHUHDUHVRPHGLIIHUHQFHVEHWZHHQ-DYDDQG&DQREMHFW RULHQWHG SURJUDPPLQJ ODQJXDJH LWVHOI $SDUW IURP WKH REMHFWRULHQWHG FRQFHSWV -DYD GLIIHUV IURP&LQYDULRXVZD\V7KHIROORZLQJOLVWVWKHGLIIHUHQFHV ♦ Java omits header files, pre-processor, goto statement and multi dimensional arrays. ♦ Like C, C++, Java does not support the pointer arithmetic. In addition, Java omits the important elements, union and structures. ♦ Java does not support the multiple inheritance. Through interfaces, we can simulate multiple inheritance. ♦ Java does not support stand-alone functions. All Java functions including the main function should be declared within the class. ♦ Although Java supports polymorphism, it does not support the operator overloading. ♦ In Java, the main function should take one parameter, which is a string type variable. The String class object itself determines the number of arguments. ♦ Java has an auto garbage collection mechanism. Therefore, we do not need to worry about freeing memory. ♦ In Java we can comment the lines by using the “/**” and “*/”. It can be used by the javadoc tool, which will be discussed later. ♦ The boolean data types, unlike in C++, are not an interpretation of the integers 0 and 1. Therefore in Java, Java boolean cannot be typecast into integers. They can have values either true or false.

Java Tools -DYDLVDFRPSOHWHSURJUDPPLQJHQYLURQPHQWDQGFRPHVZLWKLWVRZQVHWRI WRROV(DFK-DYD WRROKDVDVLJQLILFDQWIHDWXUH7KHIROORZLQJDUHWKH-DYDWRROVXVHGIRU-DYDSURJUDPPLQJ JDK

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Comp-U-Learn

7

Java Programming I Javac

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< type our Java file here with the .Java extension.>

E.g.: C:/jdk1.2/bin/javac example.java

Java

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Example 1.1 C:/jdk1.2/bin/java example

Appletviewer

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javadoc

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Comp-U-Learn

JAVA-An Introduction Jdb

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Creating an Application ,Q-DYDFUHDWLQJDQDSSOLFDWLRQSURJUDPFRQVLVWVRIWKHIROORZLQJVWHSV ♦ Create a Java Source file with .Java extension. ♦ Compile this source file by using javac compiler. ♦ Run this application by using Java interpreter. 7KH IROORZLQJ H[DPSOH LOOXVWUDWHV WKH SUHOLPLQDU\ WKLQJV DERXW FUHDWLRQ RI DQ DSSOLFDWLRQ SURJUDP

Comp-U-Learn

9

Java Programming I

Example 1.3 class first_program public static void main(String args[]) { System.out.println(“Welcome to Comp-U-Learn!”); } }

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Note In Java the source file name should be same as the class name. When we run our program, the interpreter will look for the .class file of that source file name 1RZW\SHLQWKHDERYHSURJUDPLQ1RWHSDG'26HGLWRU DQGVDYHLWDVILUVWBSURJUDPMDYDLQ -DYD·VELQGLUHFWRU\IROORZWKHVWHSVJLYHQEHORZLQWKHFRPPDQGOLQHWRJHWWKHRXWSXW 1. Compile the program using javac ( javac first_program.java) 2. Press Enter and wait until the compilation is over without any errors. 3. Then run the program using the interpreter ( java first_program) 1RZZHFDQJHWWKHRXWSXWLQWKHFRPPDQGOLQHDVIROORZV

10

Comp-U-Learn

JAVA-An Introduction

Fig 1.1

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Importing the necessary built-in Java packages Defining applet subclasses Applet implementation Passing this Java applet’s .class file into HTML file.

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11

Java Programming I

Example 1.4 import java.awt.*; import java.applet.*; public class first_applet extends Applet { public void paint(Graphics g) { g.drawString("Welcome to Comp-U-Learn!",50,20); } }

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Fig 1.2

12

Comp-U-Learn

JAVA-An Introduction

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Fig 1.3

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13

Java Programming I

Summary In this session, we learnt about the Java language and how Java is an objectoriented language. Now we can appreciate the relationship between the Java and the Internet. In this session we also learnt how Java differs from the other programming languages. After this Java preliminary, we learnt about Java tools and its uses. We also learnt to write a simple Java application program and create a simple applet.

Going Over It Again I. Fill in the Blanks

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II. State True or False

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14

Comp-U-Learn

JAVA-An Introduction III. One line Answers

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Comp-U-Learn

15

Session 2

Fundamentals of Java

On Completion of this Session We will be able to understand...

) Java Syntax & Identifiers ) Java variables and its scope ) About commenting in Java ) Java programming constructs ) Arrays & Strings in Java

In This Session...

Data types & Variables in Java

Literals, Keywords & Identifiers

Operators in Java

Expression Evaluations & Operator Precedence

Scope of Variables

Commenting in Java

Decision Making

For Loop

While & Do… While Loop

Switch & Break Statements

Arrays in Java

Strings in Java

Fundamentals of Java

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Size 1 2 4 8

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4 8 2 -

Variables in Java

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(e.g.: int

no;)

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19

Java Programming I

♦ They must not have the same name as another variable. ♦ Java is case sensitive. So int Myint, myInt, MyInt, and myint are different variables. Variable initialization

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int

number = 0;

Using Variables

7KHIROORZLQJH[DPSOHLOOXVWUDWHVWKHXVHRIYDULDEOHVLQ-DYD Example 2.1 class var_usage { public static void main(String args[]) { int a=10; double b=4.5; char c='n'; System.out.println(" This is the Usage of System.out.println(" The value of a is: " System.out.println(" The value of b is: " System.out.println(" The value of c is: " } }

Variables"); +a); +b); +c);

,QWKLVH[DPSOHWKH 6\VWHPRXWSULQWOQ VWDWHPHQW LV XVHG WR SULQW VRPH WH[W RQ WKH VFUHHQ ,Q DGGLWLRQKHUHZHDUHSULQWLQJWKHLQLWLDOL]HGYDULDEOHVVRZHKDYHWRXVH´µRSHUDWRUDORQJZLWK WKHYDULDEOHQDPH$IWHUUXQQLQJWKHDERYHSURJUDPZHJHWWKHRXWSXWDVIROORZV This is the Usage of Variables The value of a is: 10 The value of b is: 4.5 The value of c is: n

Note For printing text on consecutive lines, System.out.println statement is used. If we use the System.out.print statement, the text will be printed in the same line. 20

Comp-U-Learn

Fundamentals of Java

Literals, Keywords & Identifiers ,Q -DYD WKHUH DUH VRPH OLWHUDOV DQG UHVHUYHG ZRUGV $ OLWHUDO UHSUHVHQWV WKH YDOXH RI D FHUWDLQ W\SHZKHUHWKHW\SHGHVFULEHVKRZWKDWYDOXHEHKDYHV7KHUHDUHGLIIHUHQW W\SHVRIOLWHUDOYL] QXPHULFFKDUDFWHUERROHDQDQGVWULQJ Number

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7KHUHDUHRQO\WZRW\SHVRIERROHDQOLWHUDOV7KH\DUHWUXHDQGIDOVH Character

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Usage To insert a new line (line feed) For tab control To give backspace For carriage return To give form feed For backslash to print a “ symbol For octal For Hexadecimal For Unicode character

Key words

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21

Java Programming I

DEVWUDFWERROHDQEUHDNE\WH FDVHFDVWFDWFKFKDUFODVVFRQVWFRQWLQXH GHIDXOWGRGRXEOHHOVHH[WHQGVILQDOILQDOO\IORDWIXWXUH JHQHULFLILPSOHPHQWVLPSRUWLQQHULQVWDQFHRILQWLQWHUIDFH ORQJQDWLYHQHZQXOORSHUDWRURXWHU SDFNDJHSXEOLFSURWHFWHGDQGSULYDWH UHVWUXQUHWXUQVKRUWVWDWLFVXSHUVZLWFKV\QFKURQL]HG WKLVWKURZWUDQVLHQWWU\YDUYRLGYRODWLOHZKLOH Identifiers

7KHLGHQWLILHUVDUHWKHV\PEROVXVHGLQD-DYDSURJUDP,GHQWLILHUVFDQQRWVWDUWZLWKDQXPEHU DOWKRXJKQXPEHUVDUHDOORZHGLQVLGHLGHQWLILHUV7KHV\PEROVWKDWFDQEHXVHGDVLGHQWLILHUVLQ -DYDDUH #A ?^`>@aa_ !"´DQGHWF.

Operators in Java ,Q -DYD RSHUDWRUV FRPH LQ VHYHUDO W\SHV 7KH\ FDQ EH XVHG ZLWK YDULDEOHV WR LQGLFDWH PDWKHPDWLFDOUHODWLRQVKLSEHWZHHQWZRRUPRUHLWHPVWRFUHDWHORJLFDOVWUXFWXUHVRUWRSHUIRUP FRPSXWDWLRQV 7KH RSHUDWRUV VXSSRUWHG E\ -DYD DUH $ULWKPHWLF $VVLJQPHQW /RJLFDO DQG &RPSDULVRQ $ULWKPHWLFRSHUDWRUV $OOEDVLFDULWKPHWLFRSHUDWRUVVXFKDV DQGXQDU\RSHUDWRUVFRPHVXQGHUWKLVW\SH 7KHIROORZLQJWDEOHOLVWVWKH$ULWKPHWLFRSHUDWRUV Description Multiplication Division Addition Subtraction Modulus Increment Decrement Bit-wise complement

22

Operators * / + % ++ -~

Function Multiply the given two numbers Divide two numbers Add two numbers Subtract two numbers Determine the remainder in a division operation Increase the value of a specified variable by one Decrease the value of a specified variable by one Change the bit values of a specified variable, Converting all ones to zeros and vice versa

Comp-U-Learn

Fundamentals of Java

7KHIROORZLQJH[DPSOHVKRZVWKHXVDJHRIWKHDULWKPHWLFRSHUDWRUVLQ-DYD Example 2.2 class arithmetic { public static void main(String { int a=20; int b=10; double c=4.5; System.out.println(" The Usage System.out.println(" The value System.out.println(" The value System.out.println(" The value System.out.println(" The value System.out.println(" The value a++; b--; System.out.println(" System.out.println(" System.out.println(" System.out.println(" } }

Now, Now, Now, Now,

the the the the

args[])

of of of of of of

Arithmetic operators"); (a+b) is: " +(a+b)); (a-b) is: " +(a-b)); (a*b) is: " +(a*b)); (b+c) is: " +(b+c)); (a*c) is: " +(a*c));

second value of a is: " +a); second value of b is: " +b); final value of a is: " +(--a)); final value of b is: " +(++b));

$IWHUVDYLQJWKLVILOHDVDULWKPHWLFMDYDUXQWKHSURJUDP:HJHWWKHIROORZLQJRXWSXW 7KH8VDJHRI$ULWKPHWLFRSHUDWRUVDUHVKRZQEHORZ The value of (a+b) is: 30 The value of (a-b) is: 10 The value of (a*b) is: 200 The value of (b+c) is: 14.5 The value of (a*c) is: 90.0 Now, the second value of a is: 21 Now, the second value of b is: 9 Now, the final value of a is: 20 Now, the final value of b is: 10 Assignment operators

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23

Java Programming I int int

xy = xy + 10 xy += 10

//using normal assignment // using shortcut assignment

7KHIROORZLQJWDEOHOLVWVWKHDVVLJQPHQWRSHUDWRUVDQGIXQFWLRQV Description Assign Addition Subtraction Multiplication Division Bitwise right Bitwise left Bitwise and Bitwise xor Bitwise or

Operator = += -= *= /= >>= <<= &= ^= |=

Function Assign right operand to left operand Add right from left & assign the value Subtract right from left & assign the value Multiply two values & assign it to left operand Divide two values & assign it to left operand Perform bitwise right shift Perform bitwise left shift Perform bitwise and operation Perform bitwise xor operation Perform bitwise or operation

Logical operators

/RJLFDORSHUDWRUVDUHXVHGWRHYDOXDWHDQH[SUHVVLRQWRFKHFNZKHWKHUWKHH[SUHVVLRQLVWUXHRU IDOVH6RWKHVHORJLFDORSHUDWRUVSHUIRUPWKHHYDOXDWLRQDQGUHWXUQWKHYDOXHDVD%RROHDQW\SH Description And Or

Operator && ||

Not

!

Function returns true if both operands are true returns true if any one of operands are true. returns reverse Boolean value of the expression

Comparison operators

7KHVHDUHXVHGWRFRPSDUHWKHRSHUDQGV$%RROHDQYDOXHLVUHWXUQHGZKHQXVLQJYDULDEOHVRU OLWHUDOV ZLWK WKH FRPSDULVRQ RSHUDWRUV &RQGLWLRQDO RSHUDWLRQ LV DOVR D VSHFLDO W\SH RI FRPSDULVRQ WKDW LV RQO\ ZLWK WKH DVVLJQPHQW RSHUDWRUV 7KH WDEOH JLYHQ EHORZ OLVWV WKH FRPSDULVRQRSHUDWRUV Description Less than Greater than Equal to 24

Operator < > ==

Function return true when result is less than return true when result is greater than the compared return true when result is equal Comp-U-Learn

Fundamentals of Java

Description Less than or equal to Greater than or equal to Not equal to Conditional

Operator <= >=

Function return true when result is less than or equal return true when result is greater than or equal

!= ?:

return true when result is not equal return first value of expression when result is true.

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Expression Evaluation & Operator Precedence $QH[SUHVVLRQLVDFROOHFWLRQRIYDULDEOHVDQGRSHUDWRUVWKDWVSHFLI\DFRPSXWDWLRQ([SUHVVLRQV DUHXVHGWRSHUIRUPRSHUDWLRQVRQWKHGDWDLQDSURJUDP7KHH[SUHVVLRQVDUHQRWVWDWHPHQWV )RUH[DPSOHFRQVLGHUWKHH[SUHVVLRQ int a= 20 * 3 + 7

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Scope of Variables ,QWKLVVHFWLRQZHZLOOOHDUQDERXWWKHVFRSHRIYDULDEOHVZLWKLQDSURJUDP$YDULDEOH·VVFRSHLV WKHEORFNRIFRGHZLWKLQZKLFKWKHYDULDEOHLVDFFHVVLEOH$OVRWKHVFRSHRIDYDULDEOHGHWHUPLQHV ZKHQWKHYDULDEOHLVFUHDWHGDQGGHVWUR\HG:HFDQHVWDEOLVKWKHVFRSHRIDSDUWLFXODUYDULDEOHDW WKHWLPHRIGHFODUDWLRQ7KHIROORZLQJDUHWKHPDLQW\SHRIVFRSHRIDYDULDEOH ♦ Local variable ♦ Member variable 7KH ORFDO YDULDEOHV DUH GHFODUHG ZLWKLQ D PHWKRG RU EORFN RI FRGH LQ D PHWKRG &RQVLGHU WKH H[DPSOH:HFDQVHHWKHYDULDEOHVDEDQGF7KH\DUHGHFODUHGZLWKLQWKHPDLQPHWKRG6R Comp-U-Learn

25

Java Programming I

ZH FDQ XVH WKHVH YDULDEOHV ZLWKLQ WKH PDLQ PHWKRG RQO\ ,Q JHQHUDO D ORFDO YDULDEOH FDQ EH DFFHVVHGIURPLWVGHFODUDWLRQSDUWWRWKHHQGRIWKHFRGHEORFNLQZKLFKLWZDVGHFODUHG $ PHPEHU YDULDEOH LV D PHPEHU RI D FODVV RU DQ REMHFW DQG LV GHFODUHG ZLWKLQ D FODVV %XW LW VKRXOGQRWEHZLWKLQDQ\RIWKHFODVVPHWKRGV,IZHGHFODUHDYDULDEOHLQVLGHDPHWKRGZHFDQ DFFHVV WKDW YDULDEOH ZLWKLQ WKDW PHWKRG RQO\ :KLFK PHDQV LW ZLOO EH FRQVLGHUHG DV D ORFDO YDULDEOHRIWKDWPHWKRG7KHVWDWLFPHWKRGRIDFODVVFDQDFFHVVRQO\VWDWLFYDULDEOHVWKH\FDQ·W DFFHVVWKHYDULDEOHVZKLFKDUHGHFODUHGRWKHUZLVH

Commenting in Java ,Q -DYD SURJUDPV ZH FDQ FRPPHQW OLQHV E\ XVLQJ VLQJOH RU PXOWLSOH OLQH FRPPHQWLQJ V\QWD[ 8VLQJWKHIROORZLQJSURJUDPZHFDQXQGHUVWDQGWKHFRPPHQWLQJV\QWD[ Example 2.3: class comment { public static void main(String args[]) { int a=20; int b=10; // The following lines give us an idea about operators System.out.println(" The Usage of Arithmetic operators"); System.out.println(" The value of (a+b) is: " +(a+b)); System.out.println(" The value of (a-b) is: " +(a-b)); // Now a, b are going to be changed a++; b--; /* In the next two lines we are going to use the changed value of a, b and c */ System.out.println(" Now, the second value of a is: " +a); System.out.println(" Now,the second value of b is: " +b); } }

5XQWKHDERYHSURJUDPDQGVHHWKHRXWSXW2QO\SULQWVWDWHPHQWVJLYHQLQWKHSURJUDPZLOOEH SULQWHGLQWKHRXWSXW$Q\WKLQJWKDWDSSHDUVDIWHU´µXQWLOWKHHQGRIWKDWVLQJOHOLQHLVFDOOHG DVLQJOHOLQHFRPPHQWDQGLVLJQRUHGE\WKHMDYDFFRPSLOHU ,QDGGLWLRQDQ\WKLQJWKDWDSSHDUVDIWHU XSWR LVFDOOHGDVPXOWLSOHOLQHFRPPHQWLQJ:H FDQJLYHDQ\QXPEHURIOLQHVLQEHWZHHQWKH DQG 7KH-DYDFRPSLOHUZLOOLJQRUHDOOWKHVH OLQHV,QWKHDERYHH[DPSOHZHFDQVHHWZRW\SHVRIFRPPHQWLQJ

26

Comp-U-Learn

Fundamentals of Java

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Comp-U-Learn

27

Java Programming I

$OVRZHFDQXVHWKHVHFRQGLWLRQVMRLQWO\OLNHWUXH IDOVH __WUXH 7KHUHWXUQW\SHRIWKH DERYHFRQGLWLRQZLOOEHWUXH7KHRWKHURSHUDWRUZLOOZRUNDVIROORZV (true) = ! true = false !(false) = ! false = true if… and If.. else statements

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7KHIROORZLQJH[DPSOHZLOOJLYHWKHXVDJHRIWKHLIDQGLI«HOVHVWDWHPHQWV Example 2.4 class sample { public static void main(String args[]) { int mark1=73; int mark2=60; { if ((mark1>=75) && (mark2>=75)) { System.out.println("Grade A"); } else if (((mark1>=50) && (mark2>=50)) && ((mark1<=74) && (mark2<=74))) { System.out.println("Grade B"); } else { System.out.println("Grade C"); } } } }

28

Comp-U-Learn

Fundamentals of Java

7KHRXWSXWRIWKHDERYHSURJUDPZLOOEH*UDGH%%HFDXVHWKHJLYHQPDUNDQGPDUNEHORQJV WRWKHVHFRQGFRQGLWLRQ

For loop ,QDIRUORRSZHKDYHWRSDVVWKUHHSDUDPHWHUVVHSDUDWHGE\VHPLFRORQVIROORZHGE\WKHVHWRI VWDWHPHQWVWREHH[HFXWHGGXULQJWKHORRSRSHUDWLRQ The syntax is for (initialization; condition; increment ) { Statements }

♦ In the initialization part, we have to initialize the variable, which can be a new one declared as any of the datatypes. ♦ In second part, we have to give an expression as a condition. The return value of this expression may be true or false. Depending upon the return value, the loop statements will be executed. ♦ Last part is used to increase/decrease the counter variable. It is also optional and can be updated programmatically within the loop statements. ♦ The loop will be terminated when the condition becomes false. The following example illustrates the use of for loop. Example 2.5 class loop_example { public static void main(String args[]) { for (int i=1; i<=5;i++) { System.out.println("This is No: " +i +" execution!"); } System.out.println("Loop terminated!"); } }

7KHRXWSXWZLOOEH This is No: This is No:

1 execution! 2 execution!

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29

Java Programming I This is No: 3 execution! This is No: 4 execution! This is No: 5 execution! For Loop terminated!

While & Do… While Loop :KLOHORRSH[HFXWHVWKHVWDWHPHQWVXQWLODQH[SUHVVLRQLVWUXH:KHQWKHFRQGLWLRQLVQRORQJHU WUXHH[HFXWLRQFRQWLQXHVIURPWKHILUVWVWDWHPHQWDIWHUWKHZKLOHVWDWHPHQWV 7KHV\QWD[LV while (condition)

{ statements } ,QDGRZKLOHORRSWKHH[SUHVVLRQLVHYDOXDWHGRQO\DIWHUDOOWKHVWDWHPHQWVDUHH[HFXWHGDWOHDVW RQFH7KHV\QWD[LV do { statements } while(condition);

7KHIROORZLQJH[DPSOHLOOXVWUDWHVWKHXVDJHRIZKLOHORRS:H·OOJHWWKHRXWSXWVLPLODUWRWKH SUHYLRXVRQH Example 2.6 class loop1 { public static void main(String args[]) { int i=1; // Initialization while(i<=5) // Condition { System.out.println("This is No: " +i +" execution!"); i++; // Incrementation } System.out.println("While Loop terminated!"); } }

30

Comp-U-Learn

Fundamentals of Java

Switch & Break Statements 7KRXJKZHFDQXVH,I«HOVHVWDWHPHQWVWRGHDOZLWKPXOWLSOHFRQGLWLRQVZHFDQXVHWKHVZLWFK VWDWHPHQWVEHFDXVHWKH\DUHPRUHHIILFLHQWVLPSOHHDV\DQGUHDGDEOH7KLVRSHUDWRUDOORZVXVWR JURXS WRJHWKHU WKH FRQGLWLRQ DQG DVVRFLDWHG DFWLRQ WR SHUIRUP :KHQ WKH EUHDN NH\ZRUG LV HQFRXQWHUHGWKHUHVWRIWKHFRQGLWLRQVRIWKHVZLWFKDUHQRWHYDOXDWHG7KHV\QWD[IRUWKHVZLWFK VWDWHPHQWLV switch (variable) { case(value1): statements break; case(value2): statements break; default: statements break; }

Break

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statements

Continue

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31

Java Programming I

Example 2.7 class var_usage { public static void main(String args[]) { int i=5; switch(i) { case 1: System.out.println("Sunday!"); break; case 2: System.out.println("Monday!"); break; case 3: System.out.println("Tuesday!"); break; case 4: System.out.println("Wednesday!"); break; case 5: System.out.println("Thursday!"); break; case 6: System.out.println("Friday!"); break; case 7: System.out.println("Saturday!"); break; default: System.out.println("Holiday!"); break; } } }

Arrays in Java $QDUUD\LQ-DYDLVDQHIIHFWLYHPHDQVRIVWRULQJDFROOHFWLRQRUVHULHVRUDJURXSRIYDULDEOHVDQG UHIHUULQJWRWKHPE\DFRPPRQQDPH7KHQXPEHURIYDOXHVWKDWFDQEHVWRUHGLQDQDUUD\LV FDOOHGDUUD\VL]H(DFKYDULDEOHLVFDOOHGDVDUUD\HOHPHQWRULWHP7KHUHDUHWKUHHVWHSVWRFUHDWH DQDUUD\GHFODUDWLRQPHPRU\DOORFDWLRQDQGLQLWLDOL]DWLRQ Array declaration

/LNHDYDULDEOHZHKDYHWRGHFODUHDQDUUD\XVLQJWKHIROORZLQJV\QWD[7KHDUUD\PD\EHRIDQ\ GDWDW\SH

32

Comp-U-Learn

Fundamentals of Java <array type> <array name>

Example: int [] array1; double [] array2;

Memory allocation

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Array initialization

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int[]

array1 = new int[4]; double array2[] = new double[7];

Multidimensional Array

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33

Java Programming I

Strings in Java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xample 2.8 class exarray { public static void main(String args[]) { int array1[] = {10,20,30}; // integer type array declaration and initialization // The following are the String type array declaration and initialization String array2[] = {"First","Second","Third"}; String sample=”Hai! Students!”; for (int i=0; i<=2; i++) { System.out.println("The " +array2[i] +" element is: " +array1[i]); } System.out.println("The Extracted String is: " +(sample.substring(0,4))); } }

7KHRXWSXWZLOOEHDVIROORZV The First element is: 10 The Second element is: 20 The Third element is: 30 The Extracted String is: Hi!

34

Comp-U-Learn

Fundamentals of Java

Summary In this session we have learnt various Java data types, literals, reserved words and identifiers. Now we have a brief idea about operators and expression evaluation using operator precedence. We also tried our hands on decision making using if.. else statement, switch statement and various loops such as for/while. At the end of this session, we learnt all the concepts regarding arrays and strings in Java. We have a full-fledged knowledge about Java fundamentals and Java programming constructs.

Going Over It Again I. Fill in the Blanks

BBBBBBBBBBBVWDWHPHQWLVXVHGWRSULQWVRPHWH[WRQWKHVFUHHQ 7KHERROHDQOLWHUDOVDUHBBBBBBBBBBBDQGBBBBBBBBBBBB ,QIRUORRSBBBBBBBBBBBBBBBBBBBBDQGBBBBBBBBBBBDUHWKHSDUDPHWHUV 7KHVXEVWULQJPHWKRGLVXVHGIRUVWULQJBBBBBBBBBBB ,QGHFLVLRQPDNLQJWKHULJKWGHFLVLRQZLOOEHWDNHQGHSHQGLQJRQWKHBBBBBBBBW\SH

II. State True or False

$YDULDEOHFDQKDYHWKHVDPHQDPHDVWKDWRIDQ\UHVHUYHGZRUG ([SUHVVLRQHYDOXDWLRQGHSHQGVRQWKHRSHUDWRUSUHFHGHQFH ,Q-DYDPXOWLSOHOLQHFRPPHQWFDQEHGRQHE\ DQG :KHQWKHEUHDNNH\ZRUGLVHQFRXQWHUHGWKHUHVWRIWKHFRQGLWLRQVRIWKHVZLWFKZLOOQRWEH H[HFXWHG $UUD\VDUHSULPLWLYHGDWDW\SHV -DYDVXSSRUWVPXOWLGLPHQVLRQDODUUD\V

Comp-U-Learn

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Java Programming I III. One line Answers

:KDWDUHWKHWZRGDWDW\SHVDYDLODEOH" :KDWLVDOLWHUDOLQ-DYD" ([SODLQORFDOYDULDEOHV :KDWLVWKHXVHRI RSHUDWRU" /LVWRXWWKHPHWKRGVDYDLODEOHLQ6WULQJFODVV IV. Define the Following

3ULPLWLYHGDWDW\SH 5HIHUHQFHGDWDW\SHV ,GHQWLILHUV $UUD\V 0HPEHUYDULDEOH

36

Comp-U-Learn

Session 3

OOPs In Java

On Completion of this Session We will be able to understand...

) Traditional Programming Model ) Object Oriented Programming Approach ) Basic concepts of OOPs and its features ) Java Programming using OOPs ) Understanding various modifiers in Java ) Super and Sub classes ) Constructors and overloaded constructors ) Garbage collection in

In This Session...

Traditional Programming Model

Object Oriented Programming Approach

Features of Object Oriented Programming

Basic concepts of OOPS

Creating Classes and Objects in Java

Constructors

Garbage Collection

Finalize Method

Inheritance

Polymorphism

Recursion

Advantages of OOPs in Java

OOPs In Java

Traditional Programming Model %HIRUHDSSO\LQJWKHSURJUDPPLQJFRQVWUXFWVLQ-DYDZKLFKZHKDYHVHHQLQWKHODVWVHVVLRQZH QHHG WR NQRZ DERXW WKH FRQFHSWV RI 2EMHFW 2ULHQWHG 3URJUDPPLQJ ,Q WKLV VHFWLRQ DQG WKH VXFFHHGLQJRQHVZHDUHJRLQJWROHDUQDERXW223DQGLWVKLVWRU\,QODWHUVHVVLRQVZH·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

Main Program

Function 1

Function 2

Function 3

Function 4

Fig 3.1

7KHIROORZLQJDUHWKHFRQVWUDLQWVWKDWZHUHHQFRXQWHUHGLQWKHSURFHGXUDODSSURDFK ♦ Greater emphasis is laid on the process of the application (Sequences involved to do the task). This means that more stress is enforced on the function or methods and not on the data.

Comp-U-Learn

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Java Programming I

♦ The procedural approach does not model real world problems very well because the functions are action oriented. They don’t really correspond to the elements of the problem. ♦ Modules are tightly inter-woven, inter dependent and difficult to separate. As a result of this inter-dependency between modules, modification of one program could affect all other programs that depend on it. This led to the complexity of code especially for huge programs. ♦ Most often, applications with almost similar features have to be re-written and recompiled resulting in higher software maintenance costs as the applications lack portability to run in multiple servers and in heterogeneous environments. ♦ Most functions use global data resulting in the data moving around the system openly throughout all modules. When functions transform data from one form to another, the true state and nature of the data is not available throughout all the modules. 7KHPDMRUPRWLYDWLQJIDFWRULQWKHLQYHQWLRQRI2EMHFW2ULHQWHGDSSURDFKLVWRVDOYDJHVRPHRI WKHIODZVHQFRXQWHUHGLQWKHSURFHGXUDODSSURDFK223ODQJXDJHVVXFKDV&6PDOOWDON-DYD HWFRYHUFRPHWKHVHGUDZEDFNV7KH\DUHPRGHOHGDIWHUUHDOZRUOGFKDUDFWHULVWLFVDQGKHQFHDUH VLPSOHDQGHDV\WRXQGHUVWDQG

Object Oriented Programming Approach 223WUHDWVGDWDDVDFULWLFDOHOHPHQWLQWKHSURFHVVRISURJUDPGHYHORSPHQWDQGGRHVQRWDOORZ LWWRIORZIUHHO\DURXQGWKHV\VWHP,WWLHVGDWDPRUHFORVHO\WRWKHIXQFWLRQVWKDWRSHUDWHRQLW DQG SURWHFWV LW IURP DFFLGHQWDO PRGLILFDWLRQV IURP RXWVLGH IXQFWLRQV 223 DOORZV XV WR GHFRPSRVH D SUREOHP LQWR D QXPEHU RI HQWLWLHV FDOOHG REMHFWV DQG WKHQ EXLOGV GDWD DQG IXQFWLRQV DURXQG WKHVH HQWLWLHV 7KH RUJDQL]DWLRQ RI GDWD DQG IXQFWLRQV LQ REMHFW RULHQWHG SURJUDPVLVVKRZQEHORZ

40

Comp-U-Learn

OOPs In Java

Object A

Object B

Data

Data

Function

Function

Functio

Data

Object C

Fig. 3.2

Features of Object Oriented Programming 1. 2. 3. 4. 5. 6. 7. 8.

Emphasis is more on data rather than procedure. Programs are divided into what are known as objects. Data structures are designed so that they characterize objects. Functions that operate on data of an object are tied together in the data structure. Data is hidden and cannot be accessed by external functions. Objects may communicate with each other through functions. New data and functions can be easily added whenever necessary. Follows bottom-up approach in program design.

Note

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41

Java Programming I

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Basic Concepts of OOPS $Q\223ODQJXDJHVKRXOGVXSSRUWWKHIROORZLQJIHDWXUHV-DYDVXSSRUWVWKHVH223VFRQFHSWV H[FHSWIHZRILWVLQWHUQDOSURSHUWLHV ♦ Classes ♦ Objects ♦ Data Abstraction ♦ Data Encapsulation ♦ Inheritance ♦ Polymorphism Classes

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Note A class is a user-defined datatype that encompasses the entire set of data and code of an object. Objects

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42

Comp-U-Learn

OOPs In Java

Note Each object contains data and code to manipulate the data. Objects can interact without having to know details of each other’s data or code. Examples of objects are 5HDOREMHFWV²0DUXWKL9DQRXUFODVVURRPEDOOHWF ,PDJLQDU\²5HFRUG2UJDQL]DWLRQHWF &RPSOH[²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int k;

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♦ Data Abstraction ♦ Functional abstraction Comp-U-Learn

43

Java Programming I

,IZHWDNHDFDUDVDQH[DPSOHIRUDFODVVWKHQ Data Abstraction

(QJLQHQXPEHUVSHHGHWF Functional Abstraction

6WDUW6WRSHWF Data Encapsulation

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Creating Classes and Objects in Java ,Q-DYDZHFDQFUHDWHDQREMHFWE\FUHDWLQJDQLQVWDQFHRIDFODVV)RUH[DPSOH Date today=new Date(); Rectangle rect=new Rectangle();

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today;

7KHJHQHUDOV\QWD[LV Classname Objectname;

/HWXVWDNHDQRWKHUH[DPSOH 796HWV6RQ\3KLOLSV 44

Comp-U-Learn

OOPs In Java

+HUHZHKDYHFUHDWHGWZRREMHFWVRIWKHFODVV796HWV7KH\FDQEHLQLWLDOL]HGRUWKH\FDQEHVHW WRQXOO +RZWR,QLWLDOL]H" Sony=new TVSets; Philips=Sony;

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+RZWR,QLWLDOL]HWR1XOO Sony=null;

Note Local object variables are not automatically initialized to null. We must initialize them, either by calling new or by setting them to null. Creating a Class in Java

$ FODVV LV D EOXHSULQW RU SURWRW\SH WKDW FDQ EH XVHG WR FUHDWH PDQ\ REMHFWV 7KH FODVV FRQVWUXFWLRQKDVWZRSKDVHV ♦ Class Declaration ♦ Class Body Class Declaration

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45

Java Programming I

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Class Modifiers

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Note Package is a collection of classes grouped together. Packages are convenient for organizing our work and separating our code libraries provided with others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

46

Comp-U-Learn

OOPs In Java

Super Class and Sub Classes

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+HUHWKHFODVV0DQDJHULVDGHULYHGFODVVDQGFODVV(PSOR\HHLVDEDVHFODVV Object Class – The universal Super Class

7KHREMHFWFODVVLVWKHXOWLPDWHDQFHVWRUYHU\FODVVLQ-DYDH[WHQGV2EMHFW+RZHYHUWKHUHLV QRQHHGWRVD\ class Employee extends Object

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Comp-U-Learn

47

Java Programming I

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Member Variable Declarations

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OOPs In Java

Public

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Protected

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Java Programming I

FODVVDQGGRQRWRSHUDWHRQDQ\LQVWDQFHRIDFODVV6WDWLFPHWKRGVFDQRQO\DFFHVVVWDWLFILHOGV 6WDWLFLQLWLDOL]DWLRQRFFXUVZKHQWKHFODVVLVILUVWORDGHG6WDWLFPHWKRGVFDQQRWEHRYHUORDGHG 6WDWLFPHWKRGVEHORQJWRDFODVVDQGGRQRWRSHUDWHRQDQ\LQVWDQFHRIWKHFODVV Example 3.4 class Myclass { static private int i; static public int output() { return i; } static public void input(int j) { i=j; } }

Note Overloading refers to the existence of more than one function with the same name but with different function signature. The parameters passed to a method is called its signature. Final

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OOPs In Java

Volatile

7KLVPHDQVWKDWWKHYDULDEOHLVPRGLILHGLQYDULDEO\E\GLIIHUHQWPHWKRGVZLWKRXWDQ\FRUUHODWLRQ ,WLVQRWXVHGFRPPRQO\7KHIROORZLQJYDULDEOHGHFODUDWLRQLVDQH[DPSOHRIKRZWRGHFODUH WKDWDYDULDEOHFDQEHPRGLILHGDV\QFKURQRXVO\ Example 3.5 class Anything { volatile int r; }

Implementing Methods in Java

$PHWKRGLPSOHPHQWDWLRQFRQWDLQVWZRSDUWV ♦ Method declaration ♦ Method body Method Declaration

$PHWKRGGHFODUDWLRQSURYLGHVDORWRILQIRUPDWLRQDERXWWKHPHWKRGWRWKHFRPSLOHUWKHUXQ WLPHV\VWHPDQGWRRWKHUFODVVHVDQGREMHFWV7KLVFRQWDLQVWKHQDPHRIWKHPHWKRGWKHUHWXUQ W\SHRIWKHPHWKRGWKHW\SHRIDUJXPHQWVUHTXLUHGE\WKHPHWKRGDQGWKHPRGLILHUVIRUWKDW PHWKRG Method body

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51

Java Programming I

7KLVPHDQVWKDWWKHPHWKRGVLQWKHVXSHUFODVVHVFDQEHZULWWHQLQWKHVXEFODVVHVZLWKUHOHYDQW FKDQJHVWRPHHWWKHQHHGVRIWKHVXEFODVV%XWLQWKLVFDVHWKHRYHUULGLQJPHWKRGPXVWKDYH WKHVDPHQDPHUHWXUQW\SHDQGSDUDPHWHUOLVWLVWKHPHWKRGLWRYHUULGHV,Q-DYDDUJXPHQWVDUH SDVVHG E\ YDOXH RQO\ WR WKH PHWKRGV 3DVVLQJ YDULDEOHV E\ YDOXHV DVVXUHV WKDW WKH PHWKRGV XQLQWHQWLRQDOO\FDQQRWPRGLI\DYDULDEOH·VYDOXHWKDWLVRXWVLGHLWVVFRSH

Note When a method returns a value, the datatype of the value returned by the return statement must match the datatype that the method is actually returning. There cannot be a mismatch in the declaration and in the actual return statement. $VLPSOHH[DPSOHKHUHWRVKRZKRZWRFDOODPHWKRGLQ-DYD class ex2 { public static void main(String args[]) { System.out.println(" We are in the main function "); System.out.println(); System.out.println("Call to the method sample "); sample(); System.out.println(); System.out.println("Back to main function "); } static void sample() { int a= 10; a= a* 10; System.out.println("Now we are in the sample method "); System.out.println(a); } }

2XWSXW2IWKHSURJUDP We are in the main function Call to the method sample Now we are in the sample method 100 Back to main function

Note A method is a collection of statements that performs a series of operations. In languages like C, they are called functions.

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OOPs In Java

Constructors &RQVWUXFWRUVDUHVSHFLDOPHWKRGVSURYLGHGLQHDFK-DYDFODVVWKDWDUHUHVSRQVLEOHIRULQLWLDOL]LQJ QHZREMHFWVRIWKDWW\SH7KHQHZRSHUDWRUFUHDWHVWKHREMHFWDQGWKHFRQVWUXFWRULQLWLDOL]HVLW$ FODVV PD\ SURYLGH PXOWLSOH FRQVWUXFWRUV WR SHUIRUP GLIIHUHQW NLQGV RI LQLWLDOL]DWLRQ RQ QHZ REMHFWV$FRQVWUXFWRUWKDWWDNHVQRDUJXPHQWVLVFDOOHGDGHIDXOWFRQVWUXFWRU7KLVLVLQYRNHG DXWRPDWLFDOO\ZKHQWKHREMHFWLVLQLWLDOL]HG Example 3.7 Date today=new Date(); TVSets Philips=new TVSets(); TVSets Sony=new Sony();

:KHQ WKH FRQVWUXFWRU WDNHV DUJXPHQWV LW LV FDOOHG DQ RYHUORDGHG FRQVWUXFWRU 7KH FRPSLOHU PDNHV WKH GHFLVLRQ UHJDUGLQJ LQYRFDWLRQ RI WKH DSSURSULDWH FRQVWUXFWRU GHSHQGLQJ XSRQ WKH W\SHDQGWKHQXPEHURIDUJXPHQWVSDVVHGWRLW7KLVFRQFHSWLVFDOOHGRYHUORDGLQJ

Note Overloading refers to the concept where there are more than one function with the same name but with different parameters. These parameters may differ in number, sequence and data type of the arguments. Calls to the functions are bound according to the nature of the arguments passed. Examples 3.8 Date today = new Date(1998,10,28); TVSets Sony = new Sony(14,Portable); Rectangle rect = new Rectangle(10,10,200,200);

+HUH WRGD\ REMHFW LV LQLWLDOL]HG ZLWK DUJXPHQWV \HDU PRQWK DQG GD\ 7KH FRQVWUXFWRU ZLWK WKUHHDUJXPHQWVDYDLODEOHLQ'DWHFODVVLVLQYRNHG$QHZUHFWDQJOHUHFWRIVL]H ZLOOEHFUHDWHGDQGLQLWLDOL]HG Referring an Object variable

/HWXVVD\WKDWZHZDQWWRPRYHWKHUHFWDQJOHWRDQHZORFDWLRQ&KDQJLQJ WKHUHFWDQJOHWRD QHZORFDWLRQFRXOGEHGRQHE\WKHIROORZLQJPHWKRGV ♦ Manipulate the object’s variables directly rect.x=80; rect.y=100;

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Java Programming I

ZKHUH[\DUHWKHQHZORFDWLRQVRIWKHUHFWDQJOH *HQHUDOV\QWD[ ObjectReference.Variable

♦ Call the move method which is available in the Rectangle class rect.move(80,100);

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Garbage Collection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

Finalize Method %HIRUHDQREMHFWLVJDUEDJHFROOHFWHGWKHUXQWLPHV\VWHPFDOOVLWVILQDOL]HPHWKRG,WLVLQWHQGHG WRUHOHDVHV\VWHPUHVRXUFHVVXFKDVRSHQILOHVRURSHQVRFNHWVEHIRUHJHWWLQJFROOHFWHG2XUFODVV FDQSURYLGHIRUILQDOL]DWLRQVLPSO\E\GHFODUDWLRQRIDPHWKRGFDOOHGILQDOL]HDQGLPSOHPHQWLQJ LW)RU([DPSOH protected void finalize() { … statements }

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OOPs In Java

Inheritance ,Q UHDO OLIH ZH FDQ REVHUYH LQKHULWDQFH DOPRVW HYHU\ZKHUH $ FKLOG IRU H[DPSOH WDNHV RQ WKH FKDUDFWHULVWLFV RI WKH SDUHQWV ,QKHULWDQFH LV WKH PHFKDQLVP WKURXJK ZKLFK D FODVV FDQ EH GHILQHG LQ WHUPV RI DQ H[LVWLQJ FODVV ,QKHULWDQFH LV WKH SURFHVV E\ ZKLFK REMHFWV RI RQH FODVV DFTXLUH WKH SURSHUWLHV RI REMHFWV RI DQRWKHU FODVV ,W VXSSRUWV WKH FRQFHSW RI KLHUDUFKLFDO FODVVLILFDWLRQ7KHIROORZLQJH[DPSOHVKRZVWKHSURSHUW\LQKHULWDQFHRIREMHFWV

Vehicles Attributes: Have engine Carry people Carry luggage Used for transport

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Attributes :

Cars

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Motor Bikes

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Attributes:

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55

Java Programming I

ZKHHOHUV DQG )RXU ZKHHOHUV %RWK WKHVH FODVVHV ZLOO KDYH WKH SURSHUWLHV RI WKH JHQHUDO FODVV ´9HKLFOHVµ$JDLQWZRZKHHOHUVFODVVFRXOGEHGHULYHGRUEURNHQLQWRFODVV´0RWRU%LNH´DQG FODVV´6FRRWHUV´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

Mammals

Birds

Platypus

Fig 3.4 ,QWKLVH[DPSOHLIPDPPDOVDQGELUGVDUHWZRFODVVHVWKHQSODW\SXVH[KLELWVWKHFKDUDFWHULVWLFV RIERWKWKHVHFODVVHV Note Java does not support multiple inheritance due to difficulty in maintaining and keeping track of the code. ,Q-DYDZHFDQLQKHULWDVXSHUFODVVE\WKH.H\ZRUGH[WHQGV7KHIROORZLQJH[DPSOHLOOXVWUDWHV LQKHULWDQFHLQ-DYD class base { public String name="Peter"; public int age=23; }

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OOPs In Java class base1 extends base { private int acc_no=4566; public void disp() { System.out.println("The name is : " +name); System.out.println("The Age is : " +age); System.out.println("The account No. is : " +acc_no); } public static void main(String args[]) { base1 b = new base1(); b.disp(); } }

6DYHWKHILOHDVEDVHMDYD7KHRXWSXWLVDVIROORZV The name is : Peter The Age is : 23 The account No. is : 4566

Polymorphism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Java Programming I Shape Draw()

Circle Object

Box Object

Triangle Object

Draw(Circle)

Draw(Box)

Draw(Triangle)

Fig 3.5 /HWXVORRNDWDFRPSOHWHH[DPSOHRIDFODVVLQ-DYD7KLVH[SODLQVWKHFRQFHSWRI&RQVWUXFWRUV DQG2YHUORDGLQJFRQFHSWRI3RO\PRUSKLVP Example 3.9 // Creation of a

Class called AddSub

class AddSub { int num1,num2; public AddSub() { num1=20; num2=10; System.out.println("Default constructor invoked "); } public AddSub(int x, int y) { num1=x; num2=y; System.out.println("Overloaded Constructor Invoked "); } public int AddNum() { int num3; num3=num1 + num2; return num3; } public int SubNum()

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OOPs In Java { int num3; num3=num1-num2; return num3; } } public class ex3 { public static void main(String args[]) { AddSub a=new AddSub(); AddSub b=new AddSub(60,50); System.out.println(" The value of num1 of object a is "+ a.num1); System.out.println(" The value of num2 of object a is "+ a.num2); System.out.println(); System.out.println(" The result of addition of object a is "+a.AddNum()); System.out.println(); System.out.println(" The result of subtraction of object a is "+a.SubNum()); System.out.println(); System.out.println(" The value of num1 of object b is "+ b.num1); System.out.println(" The value of num2 of object b is "+ b.num2); System.out.println(); System.out.println(" The result of addition of object b is "+b.AddNum()); System.out.println(); System.out.println(" The result of subtraction of object b is "+b.SubNum()); } }

2XWSXWRIWKH3URJUDPLVVKRZQEHORZ Default constructor invoked Overloaded Constructor Invoked The value of num1 in object a is 20 The value of num2 in object a is 10 The The The The The The

result of addition of object a is result of subtraction of object a value of num1 in object b is 60 value of num2 in object b is 50 result of addition of object b is result of subtraction of object b

30 is 10

110 is 10

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Java Programming I Keywords this & super

,QDPHWKRGWKHNH\ZRUGWKLVUHIHUVWRWKHREMHFWRQZKLFKWKHPHWKRGRSHUDWHV:KHQWKLVLV XVHGLQVLGHDFRQVWUXFWRUWKHQWKHFRQVWUXFWRUFDOOVDQRWKHUFRQVWUXFWRURIWKHVDPHFODVV7KLV LVDFDOOWRRQHRIWKHFXUUHQWREMHFWV$JDLQLWLVUHTXLUHGRQO\ZKHQWKHUHLVDQDPELJXLW\LQWKH PHWKRGQDPHDQGLVRIWHQXVHGWRPDNHWKHLQWHQWRIWKHFRGHFOHDUHU)RUH[DPSOH class Book { int NoPages; int Weight; Book(int NoPages, int Weight) { this.NoPages=NoPages; this.weight=Weight; } }

Super

7KHNH\ZRUGVXSHUDOZD\VUHIHUVWRWKHVXSHUFODVV Example 3.10 class Employee { int salary; Employee(int i) { this.salary=i; } } class Manager extends Employee { Manager(int l) { super(l); }

+HUHWKHVXSHULVXVHGWRFDOOWKHFRQVWUXFWRURIWKHEDVHFODVV,QVKRUWWKHVXSHUUHIHUVWKHEDVH FODVV,QFDVHRIRYHUULGLQJWKHEDVHFODVVPHWKRGVLQWKHVXEFODVVHVWKHVXEFODVVHVPD\FDOOWKH EDVHFODVVPHWKRGXVLQJ Super.BaseClassMethodName();

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OOPs In Java

Recursion 5HFXUVLRQLVDJHQHUDOPHWKRGZKHUHE\DIXQFWLRQFDOOVLWVHOILQDUHSHDWHGIDVKLRQ7KLVFRXOG EH H[SODLQHG DV D UHFXUVLYH PHWKRG UHSHDWHGO\ FDOOLQJ LWVHOI XQWLO D VSHFLILF FULWHULRQ LV PHW :KHQ WKH FRQGLWLRQ EHFRPHV IDOVH WKH UHFXUVLRQ WHUPLQDWHV 7KHUH DUH DFWXDOO\ WZR W\SHV RI UHFXUVLRQSRVVLEOH 'LUHFW5HFXUVLRQ+HUHWKHVXESURJUDPVFDOOVRQO\LWVHOI ,QGLUHFW5HFXUVLRQ+HUHDVXESURJUDPFDOOVDQRWKHUVXESURJUDPZKLFKLQWXUQFDOOVWKHILUVW VXESURJUDP Example 3.11 Direct Recursion Static int recu(int x) { if (x=1) return x; else return x * recursion(x-1); } Indirect Recursion Static int even (int x) { if )x=0) return true; else return odd(x-1); } static int odd(int x) { if(x=0) return false; else return even(x-1); }

Accessor and Mutator Methods

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Java Programming I

Example of Accessor methods are as follows : int getDate() int getMonth() int getYear()

Example of Mutator methods are as follows : void setDate(int) void setMonth(int) void setYear(int)

Message Communication

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

Note Message passing supports all possible interactions between objects. Objects that send and receive messages need not be in the same process or even in the same machine

Advantages of OOPS in Java 7KURXJKLQKHULWDQFHZHFDQHOLPLQDWHUHGXQGDQWFRGHDQGH[WHQGWKHXVHRIH[LVWLQJFODVVHV :HFDQPDNHXVHRIWKHH[LVWLQJPRGXOHVWREXLOGRWKHUSURJUDPVLIWKH\ZDQWWRFRPPXQLFDWH ZLWKRQHDQRWKHUUDWKHUWKDQGHYHORSLQJWKHPRGXOHIURPWKHVFUDWFK 7KH SULQFLSOH RI GDWD KLGLQJ KHOSV WKH SURJUDPPHU WR EXLOG VHFXUH SURJUDPV WKDW FDQQRW EH WDPSHUHGE\RWKHUSURJUDPVRUHYHQWKHRWKHUFRGHLQWKHVDPHSURJUDP 62

Comp-U-Learn

OOPs In Java

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ummary In this session, we learnt basic concepts, advantages and features of OOP. We are able to apprise the traditional programming model with the Object oriented approach. The application of OOP in Java, the concept of super and sub classes tries to bring forth inheritance in Java. Also the usage of the various modifiers like public, private, abstract, final, static, volatile, transient will enable the programmer to achieve an absolute proficiency and have an concrete knowledge of OOP. The garbage collection in Java frees the programmer from worrying about the pains of memory leakage.

Going Over It Again I. Fill in the Blanks

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Java Programming I II. State True or False

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Session 4

Interfaces and Packages

On Completion of this Session We will be able to understand...

) Introduction to Interfaces ) Implementing the Interfaces ) Cloneable Interface ) About Inner classes ) Importance of packages ) Creating packages ) Access Protection ) Overview of Java Built in Packages

In This Session...

Introduction to Interfaces

What is an interface?

Intricacies in an Interface

Interface References

Extending the Interface

The Cloneable Interface

Inner Classes

Packages

Need for Packages

CLASSPATH Variable

Access Protection

Overview of Java Built-in Packages

Interfaces and Packages

Introduction to Interfaces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

What is an interface? $Q LQWHUIDFH LV YHU\ PXFK OLNH D FODVV ZLWK FRQVWDQW YDOXHV DQG PHWKRG GHFODUDWLRQV 7KH GLIIHUHQFHLVWKDWPHWKRGVLQDQLQWHUIDFHDUHRQO\GHFODUHGEXWQRWLPSOHPHQWHG$QLQWHUIDFHLV H[DFWO\ OLNH D FODVV EXW ZLWK WKH NH\ZRUG FODVV EHLQJ UHSODFHG E\ WKH NH\ZRUG LQWHUIDFH $Q LQWHUIDFH LV VLPLODU WR DQ DEVWUDFW FODVV ZLWK D UHVWULFWLRQ WKDW DOO PHWKRGV LQ DQ LQWHUIDFH DUH DEVWUDFW7KHIROORZLQJH[DPSOHH[SODLQVGHFODUDWLRQRIDQLQWHUIDFH interface ExampleInterface { void xx(); // abstract by default; no body void yy(); }

7KH DERYH H[DPSOH VXJJHVWV WKDW WKHUH DUH WZR SDUWV LQ DQ LQWHUIDFH WKH LQWHUIDFH GHFODUDWLRQ DQG WKH LQWHUIDFH ERG\ 7KH GHFODUDWLRQ SDUW FRQVLVWV RI QDPH RI WKH LQWHUIDFH DQG ZKHWKHU LW LQKHULWV IURP DQ\ RWKHU LQWHUIDFH 7KH LQWHUIDFH ERG\ FRQVLVWV RI WKH FRQVWDQW YDOXHV LQ WKH LQWHUIDFHDQGWKHGHFODUDWLRQRIWKHPHWKRGVRIWKHLQWHUIDFH1RZWRXVHWKHLQWHUIDFHDFODVV PXVWLPSOHPHQWWKHFRUUHVSRQGLQJDEVWUDFWIXQFWLRQV:HPD\GHILQHDFODVVFDOOHGVRPHDV public class some implements ExampleInterface { void xx(); // write the code here void yy(); // write the code here7 }

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Java Programming I

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Intricacies in an Interface ,QWHUIDFHV DUH XVHG WR GHILQH D SURWRFRO RI EHKDYLRU WKDW FDQ EH LPSOHPHQWHG E\ DQ\ FODVV DQ\ZKHUH LQ WKH FODVV KLHUDUFK\ /HW XV WU\ WR GLIIHUHQWLDWH EHWZHHQ LQWHUIDFHV DQG DEVWUDFW FODVVHV$EVWUDFWFODVVHVDUHXVHGRQO\ZKHQWKH\DUHVXSHUFODVVHVDQGWKHVXEFODVVHVLPSOHPHQW WKHPHWKRGV

Note In the case of interfaces, the methods can be implemented even by classes, which are not inherited. 2IWHQLQWHUIDFHVDUHWKRXJKWRIDVDQDOWHUQDWLYHWRPXOWLSOHFODVVLQKHULWDQFH:KLOHLQWHUIDFHV PD\VROYHVRPHRIWKHVDPHSUREOHPVWKDWPXOWLSOHFODVVLQKHULWDQFHGRWKH\DUHTXLWHGLIIHUHQW ,QSDUWLFXODU ♦ We cannot inherit variables from an interface ♦ We cannot inherit method implementations from an interface. ♦ The interface hierarchy is independent of the class hierarchy- classes that implement the same interface may or may not be related through the class hierarchy. This is not true for multiple inheritance. 7KHVWUHQJWKRIWKHLQWHUIDFHOLHVLQWKHIDFWWKDWDQXQUHODWHGFODVVZKLFKGRHVQRWEHORQJWRWKH KLHUDUFK\ FDQ LPSOHPHQW WKH PHWKRGV RI DQ LQWHUIDFH 7KHUHIRUH LQKHULWDQFH GRHV QRW WDNH SODFHLQWKLVFRQFHSW+HUHLVDQH[DPSOHWKDWWHOOVPRUHDERXWDQLQWHUIDFH Example 4.1 interface one { public void xx(); } interface two extends { public void yy(); }

one

class cl1 implements one { public void xx() {

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Interfaces and Packages System.out.println(“The function xx of class cl1 implements interface one“); } public void yy() { System.out.println(“Original yy in class but not in interface “); } } class cl2 implements two { public void xx() { System.out.println(“The function xx of class cl2 implements interface two “); } public void yy() { System.out.println(“The function yy of class cl2 implements interface two “); } }

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Note All methods in an interface are always public, static, final and abstract; even if we do not use the word public, they are public in one and two above. But for their implementations within a class, omitting the word public creates problems. An interface can extend multiple interfaces. 7KHVWHSVLQYROYHGLQFUHDWLQJDQLQWHUIDFHDUH 'HFODUHWKHLQWHUIDFH $GGDEVWUDFWPHWKRGVWRWKHLQWHUIDFHERG\ 6DYHWKHILOHZLWKDMDYDH[WHQVLRQ &RPSLOHWKHLQWHUIDFHFUHDWHG 7KHVWHSVLQYROYHGLQLPSOHPHQWLQJDQLQWHUIDFHDUH 'HFODUHWKHFODVVDQGXVHWKHLPSOHPHQWNH\ZRUGIROORZHGE\WKHQDPHRIWKHLQWHUIDFH ,PSOHPHQWHYHU\DEVWUDFWPHWKRGWKDWKDVEHHQGHFODUHGZKLOHFUHDWLQJWKHLQWHUIDFH 6DYHWKHILOHZLWKDMDYDH[WHQVLRQ &RPSLOHWKHDSSOHWRUDSSOLFDWLRQFUHDWHG

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Java Programming I

7KH IROORZLQJ DUH VRPH RI WKH JXLGHOLQHV WR EH IROORZHG ZKLOH FUHDWLQJ DQG LPSOHPHQWLQJ LQWHUIDFHV ♦ An interface can be declared as public, whereby it can be implemented even outside a package. ♦ An interface cannot be considered a substitute for multiple inheritance, which is not supported by Java. ♦ While declaring members in an interface, we may not use the private and protected access specifiers. ♦ Constants declared in an interface are implicitly public, static and final. ♦ All methods declared in an interface are implicitly public and abstract. ♦ A class can implement as many interfaces as required with each interface name being separated by a comma(,).

Note If the parent class already implements an interface, its subclasses do not need to explicitly use the implement keyword. $VDPSOHSURJUDPWRVKRZWKHZRUNLQJRIDQLQWHUIDFH Example 4.2 package Display; public interface DisplayInterface { public String GetDlsplayText(); //no implementation of this method } // This applet implements the method declared in the interface import java.awt.*; import java.applet.*; import java.lang.*; import Display.DisplayInterface; public class ex13 extends Applet implements DisplayInterface { public void paint(Graphics g) { String str=GetDisplayText(); g.drawString(str,80,100); } public String GetDisplayText() { return " Display Text "; } }

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Interfaces and Packages

Note Member declarations in an interface disallow some of the use of declaration modifiers and discourage the use of others. We may not use transient, volatile or synchronized in a member declaration in an interface. Also, we may not use the private and protected specifiers when declaring members of an interface.

Interface References :HFDQGHFODUHYDULDEOHVDVREMHFWUHIHUHQFHVWKDWXVHDQLQWHUIDFHUDWKHUWKDQDFODVVW\SH$Q\ LQVWDQFHRIDFODVVWKDWLPSOHPHQWVWKHGHFODUHGLQWHUIDFHFDQEHVWRUHGLQVXFKDYDULDEOH:KHQ ZHFDOODPHWKRGWKURXJKRQHRIWKHVHUHIHUHQFHVWKHFRUUHFWYHUVLRQZLOOEHFDOOHGEDVHGRQWKH DFWXDOLQVWDQFHRIWKHLQWHUIDFHEHLQJUHIHUUHGWR7KLVLVRQHRIWKHNH\IHDWXUHVRILQWHUIDFHV 7KHPHWKRGWREHH[HFXWHGLVORRNHGXSG\QDPLFDOO\DWUXQWLPHDOORZLQJFODVVHVWREHFUHDWHG ODWHU WKDQ WKH FRGH ZKLFK FDOOV PHWKRGV RQ WKHP 7KH FDOOLQJ FRGH FDQ GLVSDWFK WKURXJK DQ LQWHUIDFHZLWKRXWKDYLQJWRNQRZDQ\WKLQJDERXWWKHFDOOHGFRGH Example 4.3 interface Iface { void callfn(int i); } class One implements Iface { public void callfn(int a) { System.out.println(“Calling the callfn with “ + a); } } class Two implements Iface { public void callfn(int a) { System.out.println(“Call from class two of method of callfn”); System.out.println(“a squared is “ + (a * a)); } } class ex12 { public static void main(String args[]) { Iface i=new One(); Two j=new Two(); i.callfn(100);

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Java Programming I i=j; i.callfn(100); } }

Extending the Interface $QLQWHUIDFHFDQLQKHULWDQRWKHUE\XVHRIWKHNH\ZRUGH[WHQGV7KHV\QWD[LVWKHVDPHDVIRU LQKHULWLQJFODVVHV:KHQDFODVVLPSOHPHQWVDQLQWHUIDFHWKDWLQKHULWVDQRWKHULQWHUIDFHLWPXVW SURYLGHLPSOHPHQWDWLRQVIRUDOOPHWKRGVGHILQHGZLWKLQWKHLQWHUIDFHLQKHULWDQFHFKDLQ7KLVFDQ EHLOOXVWUDWHGWKURXJKDQH[DPSOH Example 4.4 interface A { void meth1(); void meth2(); } interface B extends A { void meth3(); } class cl1 implements B { public void meth1() { System.out.println(“implementing method 1 in Interface A”); } public void meth2() { System.out.println(“implementing method 2 in Interface A”); } public void meth3() { System.out.println(“implementing method 3 in Interface B”); } } class ex14 { public static void main(String args[]) { cl1 obj=new cl1(); obj.meth1(); obj.meth2(); obj.meth3(); } }

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Interfaces and Packages

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The Cloneable Interface :KHQ ZH PDNH D FRS\ RI WKH YDULDEOH WKH RULJLQDO DQG WKH FRS\ DUH UHIHUHQFHV WR WKH VDPH REMHFW7KLVPHDQVDFKDQJHWRHLWKHUYDULDEOHDOVRDIIHFWVWKHRWKHU Day Bday=new Day(1998,8,16); Day d=Bday; d.advance(100); //Oops will also change Bday

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Bday

Day

D

Day 16 Month 8 Year 1998

Fig. 4.1 ,IZHZRXOGOLNH'WREHDQHZREMHFWWKDWEHJLQVLWVOLIHEHLQJLGHQWLFDOWR%GD\EXWZKRVHVWDWH FDQGLYHUJHRYHUWLPHWKHQZHXVHWKHFORQH PHWKRG Day Bday=new Bday(1998,8,16); Day d=(Day)Bday.clone(); // must cast because clone() returns an Object d.advance(100); //Bday will not be changed.

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Java Programming I

Day

Bday

Day 16 Month 8 Year 1998

Day

D

Day 16 Month 8 Year 1998

Fig. 4.2

Inner Classes $QLQQHUFODVVLVDFODVVWKDWLVGHILQHGLQVLGHDQRWKHUFODVV7KHQHHGIRULQQHUFODVVHVFDQEH VWDWHGDVIROORZV ♦ An object of an inner class can access the implementation of the object that created it – including data that would otherwise be private. ♦ Inner classes can be hidden from other classes in the same package. ♦ Anonymous inner classes are handy when we want to define callbacks on the fly. ♦ Inner classes are very convenient when we are writing event-driven programs. Example 4.5 class LinkedList { ............ ............. ................... private: class Node

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Interfaces and Packages { public Node *Next; int data; } class Iterator { public : void insert(int x); int erase(); } ................. }

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Note An object that comes from an inner class has an implicit reference to the outer class object that instantiated it. Through this pointer, it gains access to the total state of the outer object. A static inner class can be used whenever the inner class does not need to access an outer class.

Packages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import java.awt.*; import java.applet.*; import java.awt.Button;

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Java Programming I

Need for Packages /HW XV VHH WKH QHHG IRU SDFNDJHV EHIRUH WU\LQJ WR GHILQH D SDFNDJH ,I WKH FRQFHSW RI LPSRUW VWDWHPHQWGRHVQRWH[LVWLQ-DYDZHDQGKDGWRIRUH[DPSOHFUHDWHD%XWWRQREMHFWZHZRXOG KDYHWRVD\ java.awt.Button MyButton=new java.awt.Button(“sample”);

7KLVLVDYHU\WHGLRXVZD\RIFUHDWLQJD%XWWRQZLWKWKHDGGLWLRQDORYHUORDGRIQHHGLQJWRNQRZ WKHIXOO\TXDOLILHGQDPHVZKHQUHIHUULQJWRDFODVVRI-DYD7KHVDPHWKLQJFRXOGEHDSSURDFKHG LQDVWUDLJKWIRUZDUGPDQQHU import java.awt.button; ............................................. ............................................. Button MyButton = new Button(“sample”);;

7RFUHDWHSDFNDJHVVLPSO\LQFOXGHDSDFNDJHFRPPDQGDVWKHILUVWVWDWHPHQWLQD-DYDVRXUFH ILOH $Q\ FODVV GHFODUHG ZLWKLQ WKDW ILOH ZLOO EHORQJ WR WKH VSHFLILHG SDFNDJH 7KH SDFNDJH VWDWHPHQWGHILQHVDQDPHVSDFHLQZKLFKFODVVHVDUHVWRUHG,IZHRPLWWKHSDFNDJHVWDWHPHQW WKHQWKHFODVVQDPHVDUHSXWLQWRDGHIDXOWSDFNDJHZKLFKKDVQRQDPH$WWKHEHJLQQLQJRIWKH FODVVGHFODUDWLRQDGGWKHIROORZLQJFRGH package Packagename;

Example package pkg;

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Interfaces and Packages

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CLASSPATH Variable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napshot on Packages

♦ As default, every class belongs to some package in Java. ♦ A package statement before the class statement is necessary. ♦ Two or more packages can be grouped. This creates a hierarchy of packages. ♦ Package hierarchy is denoted by writing the dot (.) after every level; aaa.bbb.ccc means that the package ccc is in the bbb package which is in the aaa package. ♦ Java restriction is that we should keep the packages/classes into corresponding directories/files. ♦ It is possible to create a class called cla in ccc as well as in bbb or in ttt. There is no conflict; they actually have different full names to be qualified. ♦ A package can contain only one public class.

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Java Programming I

Example 4.6 package mainpack; public class Class1 { public static void meth1() { System.out.println(“Hello Friends”); } }

&UHDWHDGLUHFWRU\FDOOHGPDLQSDFNXQGHUELQDQGVDYHWKLVILOHDV&ODVVMDYD package mainpack.child; public class Class2 { public static void meth2() { System.out.println(“Good Bye Friends”); } }

1RZFUHDWHDVXEGLUHFWRU\FDOOHGFKLOGXQGHUWKHGLUHFWRU\PDLQSDFN6DYHWKLVILOHDV&ODVVMDYD LQWKHVXEGLUHFWRU\FKLOG1RZXQGHUELQGLUHFWRU\RSHQDQHZILOHDQGZULWHWKHIROORZLQJFRGH import mainpack.*; import mainpack.child.*; class ex14 { public static void main(String args[]) { Class1.meth1(); Class2.meth2(); } }

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Interfaces and Packages

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Subclasses in the same package Non subclasses in the same package Sub classes in different packages Classes that are neither in the same package nor subclasses

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Comp-U-Learn

79

Java Programming I

1RQHQRWVSHFLI\LQJDQ\WKLQJ Private Public Private protected Protected 7KHUXOHVIRUXVLQJWKHVHDWWULEXWHVDUHDVIROORZV ,I ZH GRQ·W VSHFLI\ DQ\WKLQJ WKLV FODVV DQG WKH GDWDPHWKRGV GHILQHG LQVLGH LW DUH YLVLEOH DFFHVVLEOH WKURXJKRXWWKHSDFNDJHFRQWDLQLQJWKLVFODVVYLVLEOHDFFHVVLEOHWR76313 ,IZHGHFODUHVRPHWKLQJWKLVFODVVRUWKHGDWDPHWKRGVGHILQHGLQVLGHLW DVSULYDWHLWLVYLVLEOH DFFHVVLEOH RQO\ LQ WKLV FODVV YLVLEOH WR 7 7KH ZRUG SULYDWH LV JHQHUDOO\ XVHG IRU KLGLQJ LQIRUPDWLRQIURPRWKHUFODVVHV ,IZHGHFODUHVRPHWKLQJDVSULYDWHSURWHFWHGLWLVYLVLEOHDFFHVVLEOH LQVLGHDOOWKHVXEFODVVHVLQ WKLVSDFNDJHDVZHOODVLQRWKHUSDFNDJHVYLVLEOHWR76362 ,I ZH GHFODUH VRPHWKLQJ DV SURWHFWHG LW LV YLVLEOH LQVLGH DOO FODVVHV RI WKLV SDFNDJH DQG DOVR LQVLGHWKHVXEFODVVHV RIRWKHUSDFNDJHVYLVLEOHWR 763136R ,WLVQRWYLVLEOHRQO\IRUWKH QRQVXEFODVVHVRIRWKHUSDFNDJHVQRWYLVLEOHWR12 ,IZHGHILQHVRPHWKLQJSXEOLFLWLVYLVLEOHHYHU\ZKHUHYLVLEOHWR763136212

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Java.applet Java.awt Java.beans Java.io Java.lang Comp-U-Learn

Interfaces and Packages

♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦

Java.math Java.net Java.rmi Java.security Java.sql Java.text Java.util Com.sun.java.swing Com.sun.java.image.codec.jpeg Com.sun.java.accessibility Org.omg.CORBA

The java.applet

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81

Java Programming I

The java.lang

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Comp-U-Learn

Interfaces and Packages

Summary Interfaces are declared like classes but using the keyword interface. Interface has two parts the interface declaration and the interface body. Any class outside the hierarchy can implement interfaces. Interfaces are mainly used to draw a similarity between unrelated classes. Interfaces are not a substitute for multiple inheritance. All the methods declared in the interface are abstract. Implementing the interface results in the implementation of the methods declared in the interface. A package is a group of classes similar to the libraries offered by most programming languages. Packages help simplify programming and remove the overhead of remembering fully qualified package names to refer a class. The keyword package identifies the package. The import statement is used to import classes of a package in other programs. Some of the standard Java packages are java.applet, java.lang, java.net, java.util, java.awt and java.io.

Going Over It Again I. Fill in the Blanks

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83

Java Programming I

III. One line Answers

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84

Comp-U-Learn

Session 5

Streams and File Handling

On Completion of this Session We will be able to understand...

) Stream class and its functions ) System Properties ) Input Stream and its methods ) Output Streams and its methods ) Directory Structure ) File Input and Output Streams ) Buffered Streams & Filtered Streams

In This Session...

Java Stream Class

Print Stream

System Properties

Input and Output Streams

Files and Directories

File Input and Output Streams

Data Input and Output Streams

Filtered Streams

Buffered Streams

Pushback Input Streams

Random Access File

Reader and Writer Classes

Streams and File Handling

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87

Java Programming I Java’s Stream Input Output Classes

Stream Class BufferedInputStream BufferedOutputStream ByteArrayInputStream ByteArrayOutputStream DataInputStream DataOutput Stream File File Descriptor FileInputStream FileOutputStream FilterInputStream FilterOutputStream InputStream LineNumberInputStream OutputStream PipedInputStream PipedOutputStream PrintStream PushbackInputStream RandomAccessFile SequenceInputStream

Stream Tokenizer String BufferInputStream

Definition Buffered input stream Buffered output stream Input stream that reads from a byte array Output stream that writes to a byte array An input stream that contains methods for reading Java standard data types An output stream that contains methods for writing Java standard data types Deals directly with files and the file system Deals with record pointers, file descriptions and file access mechanisms Input stream that reads from a file Output stream that writes to a file Implements Input Stream Implements Output Stream Abstract class that describes stream input Input stream that counts lines Abstract class that describes stream output Input pipe Output pipe Output stream that contains print() and println() Input stream that supports one-byte “unget” which returns a byte to the input stream Supports random access file I/O Input stream that is a combination of two or more input streams which will be read sequentially, one after the other Tokenizing input stream Input streams that read from a string

Built-in streams in Java

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Streams and File Handling

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Comp-U-Learn

89

Java Programming I

Example 5.1 import java.io.FileInputSteeam; import java.util,Properties; class PropertiesTest { public static void main(String args[]) { try { FileInputStream pfile=new FileInputStream(“MyProps.txt”); Properties p=new Properties(System.getProperties()); p.load(pfile); System.setProperties(p); System.getProperties().list(System.out); } catch(java.io.FileNotFoundException e) { System.err.println(“Cannot find the file MyProps.txt”); } catch(java.io.IOException e) { System.err.printlln(“Input Output Error “); } } }

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Note Finalization can be forced to occur by the method System.runFinalization and the garbage collector can be made to run at anytime using System.gc(). Method read()

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90

Comp-U-Learn

Streams and File Handling

Example 5.2 import java.io.*; class ex22 { public static void main(String args[]) throws IOException { char c; System.out.println("enter characters, q to quit. "); do{ c=(char)System.in.read(); System.out.println(c); }while(c!='q'); } }

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Reading a String

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Java Programming I

Example 5.3 import java.io.*; class ex23 { public static void main(String args[]) throws IOException { DataInputStream in=new DataInputStream(System.in); String str; System.out.println("Enter lines of text "); System.out.println("Enter 'End' to quit"); do{ str=in.readLine(); System.out.println(str); }while(!str.equals("End")); } }

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$QRWKHUH[DPSOHWRVKRZWKHEHKDYLRURI,2VWUHDPVLVJLYHQEHORZ Example 5.4 import java.io.*; class ex24 { public static void main(String args[]) throws IOException { DataInputStream in=new DataInputStream(System.in); String str[]=new String[50]; System.out.println("Enter lines of text "); System.out.println("Enter 'End' to quit"); for(int i=0;i<50;i++) { str[i]=in.readLine(); if(str[i].equals("End")) break;

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");

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Java Programming I File File File File

f1=new f2=new f3=new f3=new

File(“/”); File(“/”, “autoexec.bat”); File(f1,”autoexec.bat”); File(“user”,”autoexec.bat”);

Note The Java convention is to use the UNIX and URL style forward slash for path separators. Methods of File Class

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7KLVPHWKRGUHWXUQVWUXHLIWKHILOHKDVDQDEVROXWHSDWKIDOVHLIUHODWLYH $QH[DPSOHWRVKRZWKHZRUNLQJRIYDULRXVPHWKRGV&UHDWHDVLPSOHWH[WILOHFDOOHGGXPP\W[W XQGHUF?H[DPSOHWRUXQWKLVSURJUDP Example 5.5 import java.io.File; class ex25 { static void a(String s) { System.out.println(s); } public static void main(String args[]) { File f1=new File("c:/example/dummy.txt"); a("File Name : " + f1.getName()); a("Path : "+f1.getPath()); a("Absolute Path is :" + f1.getAbsolutePath()); a("Parent : " +f1.getParent()); a(f1.exists() ? "File exists " : "File does not exist "); a(f1.canWrite() ? "is writable " : " is not writable "); a(f1.canRead() ? "readable " : " is not readable"); a("is" +(f1.isDirectory() ? "" : "not" +" a directory")); a(f1.isFile() ? "is normal file" : "is not a normal file"); a(f1.isAbsolute() ? "is absolute " : "is not absolute "); a("file last modified : " + f1.lastModified()); a("file size : " + f1.length() + "Bytes "); } }

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Java Programming I

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Java Programming I } public boolean accept(File dir,String fname) { return fname.endsWith(ex); } }

6DYHWKLVILOHZLWKWKHH[WHQVLRQ2QO\([WMDYDXQGHUELQ import java.io.*; class ex27 { public static void main(String args[]) { String dirname="C:/example"; File f1=new File(dirname); FilenameFilter ff=new OnlyExt("doc"); String s[]=f1.list(ff); for(int i=0; i<s.length;i++) System.out.println(s[i]); } }

7KHRXWSXWRIWKHSURJUDPH[MDYDLVDVIROORZV C:\jdk1.2\bin>javac ex27.java C:\jdk1.2\bin>java ex27 OOPs In Java.doc ~$ided tour-3 qns.doc ~$terfaces.doc ~$treams.doc Answers to guide tour-3.doc guided tour-3 qns.doc Interfaces.doc Streams.doc Cover Page.doc C:\jdk1.2\bin>

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Java Programming I System.out.println("Press enter after each line to get input into the program "); for(int i=0;i<150;i++) inp[i]=(byte)System.in.read(); return inp; } public static void main(String args[]) throws Exception { byte input[]=getInput(); OutputStream f=new FileOutputStream("c:/jdk1.2/bin/new.txt"); for(int i=0;i<150;i++) f.write(input[i]); f.close(); int size; InputStream fi=new FileInputStream("c:/jdk1.2/bin/new.txt"); size=fi.available(); for(int i=0;i<size;i++) System.out.print((char)fi.read()); f.close(); } }

2XWSXWRIWKHSURJUDP C:\jdk1.2\bin>java ex28 enter text only 10 bytes Press enter after each line to get input into the program Serialized Serialized C:\jdk1.2\bin>

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Example 5.9 import java.io.*; class ex31 { public static void main(String args[]) throws IOException { BufferedReader d=new BufferedReader (new InputStreamReader(new FileInputStream("c:/example/dummy.txt"))); DataOutputStream o=new DataOutputStream (new FileOutputStream("c:/uma/dummy1.txt")); String l; while((l=d.readLine())!= null) { String a=l.toUpperCase(); System.out.println(a); o.writeBytes(a+ "\r\n"); } d.close(); o.close(); } }

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Java Programming I

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Streams and File Handling

7KHRXWSXWRIWKHSURJUDPLV C:\jdk1.2\bin>java ex29 enter 10 chars and then press enter key these will be converted into uppercase characters Acrobatics accepted characters into an array displaying characters in the array A c r o b a t i c s Converted to upper case characters ACROBATICS

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Java Programming I

Buffered Streams %XIIHUHG VWUHDPV H[WHQG WKH ILOWHUHG VWUHDP FODVVHV E\ DWWDFKLQJ D PHPRU\ EXIIHU WR WKH ,2 VWUHDPV 7KLV EXIIHU DOORZV -DYD WR GR ,2 RSHUDWLRQV RQ PRUH WKDQ D E\WH DW D WLPH KHQFH LQFUHDVLQJSHUIRUPDQFH%HFDXVHWKHEXIIHULVDYDLODEOHVNLSSLQJPDUNLQJDQGUHVHWWLQJRIWKH VWUHDPEHFRPHVSRVVLEOH BufferedInputStream

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Pushback Input Stream 3XVKEDFN LV XVHG RQ DQ LQSXW VWUHDP WR DOORZ D FKDUDFWHU WR EH UHDG DQG WKHQ UHWXUQHG LH SXVKHGEDFN WRWKHVWUHDP7KH3XVKEDFN,QSXW6WUHDPFODVVLPSOHPHQWVWKLVLGHD,WSURYLGHVD PHFKDQLVPWRSHHNDWZKDWLVFRPLQJIURPDQLQSXWVWUHDPZLWKRXWGLVUXSWLQJLW+RZHYHUDQ\ DWWHPSWWRSXVKEDFNPRUHWKDQDVLQJOHFKDUDFWHUUHVXOWVLQDQ,2([FHSWLRQEHLQJWKURZQ$Q H[DPSOHWRVKRZWKH3XVKEDFN,QSXW6WUHDPDQGXQUHDG Example 5.11 import java.io.*; class ex30 { public static void main(String args[]) throws IOException { String s="if (a== 4) a=0 \n"; byte buf[]=new byte[s.length()]; s.getBytes(0,s.length(),buf,0); ByteArrayInputStream in=new ByteArrayInputStream(buf);

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Streams and File Handling PushbackInputStream f=new PushbackInputStream(in); int c; while((c=f.read()) !=-1) { switch(c) { case '=': if((c=f.read())=='=') System.out.print(".eq."); else { System.out.print("<-"); f.unread(c); } break; default: System.out.print((char)c); break; } } } }

7KHRXWSXWRIWKHSURJUDPLV C:\jdk1.2\bin>java ex30 if (a.eq. 4) a<-0

Stream Tokenizer

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3. InputStreamReader

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Streams and File Handling 4. BufferedReader Class

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$QH[DPSOHWRVKRZ5HDGHUDQG:ULWHUFODVVHV Example 5.12 import java.io.*; public class ex50 { public static void main(String args[]) { try { BufferedReader in = new BufferedReader(new FileReader(args[0])); String s,s1 = new String(); while ((s=in.readLine())!=null) s1+=s+'\n'; in.close(); BufferedReader stdin = new BufferedReader (new InputStreamReader(System.in)); System.out.println("Enter a Line"); System.out.println("Usage of buffered reader and InputStreamReader"); System.out.println(stdin.readLine()); StringReader intwo = new StringReader(s1); int c; System.out.println("Printing individual chars of a file " + args[0]); while ((c=intwo.read())!=-1) System.out.println((char)c); BufferedReader in4 = new BufferedReader(new StringReader(s1)); PrintWriter p = new PrintWriter (new BufferedWriter(new FileWriter("str1")));

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Java Programming I while((s=in4.readLine())!=null) p.println("Output "+s); p.close(); } catch(IOException e) { } } }

2XWSXWRIWKHSURJUDP C:\jdk1.1.5\bin>java ex50 ex41.java Enter a Line Usage of buffered reader and InputStreamReader india is my country // The contents of the file ex41.java will be displayed character by character, also the contents of the file will be stored in “str1”.

Summary The Streaming interface in Java provides a clean abstraction for a complex and often cumbersome task. The composition of the filtered stream classes allow us to dynamically build the custom streaming interface to suit our data transfer requirements. Streams are a method of receiving and sending information. The InputStream, OutputStream, DataStreams, PrintStream, RandomAccessFile Streams, BufferedInputStream and BufferedOutputStream are some of the important File Stream classes in Java. Java programs written to adhere to the abstract, high level InputStream and OutputStream classes will function properly in the future even when new and improved concrete stream classes are invented.

Going Over It Again I. Fill in the Blanks

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Streams and File Handling

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111

Session 6

Exception Handling and MultiThreading

On Completion of this Session We will be able to understand...

) Concepts of errors ) Need To handle errors ) Error Handling in Java ) Uncaught exceptions ) Usage of try, catch, finally and throw blocks ) The Throwable Class ) About Multithreading

In This Session...

Exception Handling – An Insight

Advantages of Exception Handling

Uncaught Exceptions

Multiple Catch Clauses

Implicit and Explicit Exceptions

Java.lang.Throwable

Finally Clause

Creating Own Exception subclasses

MultiThreading

Thread States

Thread Priority

Daemon Threads

Exception Handling and MultiThreading

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Advantages of Exception Handling -DYDSURJUDPVKDYHWKHIROORZLQJDGYDQWDJHRYHUWUDGLWLRQDOHUURUPDQDJHPHQWWHFKQLTXHV ♦ ♦ ♦ ♦ ♦

Separating Error handling Code from Regular Code Propagating Errors Up the Call Stack Grouping Error Types and Error Differentiation Allows fixing the errors It prevents the program from automatic termination

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RunTime Exception

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Java Programming I

Uncaught Exceptions /RRNDWWKHSURJUDPJLYHQEHORZ,WKDVZLOOIXOO\LQFOXGHGDGLYLVLRQE\]HUR Example 6.1 class ex61 { public static void main(String args[]) { int d=0; int a=42/d; } }

7KHRXWSXWRIWKHSURJUDPLV C:\jdk1.2\bin>javac ex61.java C:\jdk1.2\bin>java ex61 Exception in thread "main" java.lang.ArithmeticException: / by zero at ex61.main(ex61.java:6) C:\jdk1.2\bin>

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Exception Handling and MultiThreading This is the general form of n exception handling try { //Block of code to monitor for errors } catch(ExceptionType1 exObj) { // exception handler for Exceptiontype 1 } catch(ExceptionType2 exObj2) { //exception handler for exception type 2 } //.......................... ........................... finally { // block of code to be executed before try block ends }

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Note We can throw many exceptions in one method, but we cannot throw exceptions inherited from Error class and those from RunTimeException $VDPSOHSURJUDPWRLOOXVWUDWHWKHXVDJHRIWKURZLQJDQH[FHSWLRQ Example 6.2 class ex62 { public static void main(String args[]) { System.out.println("enter a character "); char c=(char)System.in.read(); } }

2XWSXWRIWKHSURJUDP C:\jdk1.2\bin>javac ex62.java Ex62a.java:6: Exception java.io.IOException must be caught, or it must be declared in the throws clause of this method. char c=(char)System.in.read(); ^ 1 error

Comp-U-Learn

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Java Programming I

1RZZHFDPUHZULWHWKHSURJUDPDVVKRZQEHORZDQGVHHWKHRXWSXW class ex62 { public static void main(String args[]) throws java.io.IOException { System.out.println("enter a character "); char c=(char)System.in.read(); } }

7KHRXWSXWRIWKHSURJUDPQRZLV C:\jdk1.2\bin>java ex62 java C:\jdk1.2\bin>java ex62 Enter a character i

1RZZHFDQUHZULWHWKHSURJUDPH[MDYDZKLFKWKURZVDQ$ULWKPHWLF([FHSWLRQ class ex61 { public static void main(String args[]) { int d,a; try { d=0; a=42/d; System.out.println("Test to see the try block } catch (ArithmeticException e) { System.out.println("Division by zero "); System.out.println("Inside catch block "); } System.out.println("After catch block "); } }

7KHRXWSXWRIWKHSURJUDPLV C:\jdk1.2\bin>javac ex61.java C:\jdk1.2\bin>java ex61 Division by zero Inside catch block After catch block C:\jdk1.2\bin>

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Exception Handling and MultiThreading

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Note Curly braces must surround the statements that are protected in a try statement. That is, they must be within a block. We cannot use try on a single statement. Displaying the description of an Exception

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7KLVZLOOJLYHWKHRXWSXW C:\jdk1.2\bin>java ex62 Division by zero Inside catch block Exception :java.lang.ArithmeticException: / by zero After catch block C:\jdk1.2\bin>

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Java Programming I

Multiple Catch Clauses 0RUH WKDQ RQH H[FHSWLRQ FRXOG EH UDLVHG E\ D VLQJOH SLHFH RI FRGH 7R KDQGOH WKLV W\SH RI VLWXDWLRQZHFDQVSHFLI\WZRRUPRUHFDWFKFODXVHVHDFKFDWFKLQJDGLIIHUHQWW\SHRIH[FHSWLRQ :KHQDQH[FHSWLRQLVWKURZQHDFKFDWFKVWDWHPHQWLVLQVSHFWHGLQRUGHUDQGWKHILUVWRQHZKRVH W\SHPDWFKHVWKDWRIWKHH[FHSWLRQH[HFXWHG$IWHURQHFDWFKVWDWHPHQWH[HFXWHVWKHRWKHUVDUH E\SDVVHGDQGH[HFXWLRQFRQWLQXHVDIWHUWKHWU\FDWFKEORFN7KHIROORZLQJH[DPSOHWUDSVWZR GLIIHUHQWH[FHSWLRQW\SHV Example 6.3 class ex63 { public static void main(String args[]) { try{ int a=args.length; System.out.println("a = " +a); int b=42/a; int c[]= {1}; c[42]=99; System.out.println("Test to see the try } catch (ArithmeticException e) { System.out.println("Division by zero " } catch(ArrayIndexOutOfBoundsException e) { System.out.println("Array index :" + e } System.out.println("After try and catch } }

block

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7KHRXWSXWRIWKHSURJUDP C:\jdk1.2\bin>java ex63 a = 0 Division by zero java.lang.ArithmeticException: / by zero After try and catch block C:\jdk1.2\bin>java ex63 neem a = 1

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Exception Handling and MultiThreading

Example 6.4 class ex64 { public static void main(String args[]) { int d,a; try{ d=0; a=42/d; System.out.println("Test to see the try block "); } catch(Exception e) { System.out.println("General exception raised in catch " +e); } catch (ArithmeticException e) { System.out.println("Division by zero "); System.out.println("Inside catch block "); System.out.println("Exception :"+e); } System.out.println("After catch block "); } }

7KHRXWSXWRIWKHDERYHSURJUDPLVDVIROORZV C:\jdk1.2\bin>javac ex64.java Ex64.java:15: catch not reached. catch (ArithmeticException e) ^ 1 error C:\jdk1.2\bin>

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Exception Handling and MultiThreading try{ if (a==1) a=a/(a-a); if (a==2) { int c[]={1}; c[42]=99; } } catch(ArrayIndexOutOfBoundsException e) { System.out.println("Array index out of bounds : " +e); } }catch(ArithmeticException e) { System.out.println("Divide by 0 : " +e); } } }

7KHRXWSXWRIWKHSURJUDP C:\jdk1.2\bin>java ex65 Divide by 0 : java.lang.ArithmeticException: / by zero C:\jdk1.2\bin>java ex65 Uma a = 1 Divide by 0 : java.lang.ArithmeticException: / by zero C:\jdk1.2\bin>java ex65 Uma Uma2 a = 2 Array index out of bounds : java.lang.ArrayIndexOutOfBoundsException: 42 C:\jdk1.2\bin>

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Java Programming I

WKDW PDWFKHV WKH W\SH RI WKH H[FHSWLRQ ,I LW ILQGV D PDWFK FRQWURO LV WUDQVIHUUHG WR WKDW VWDWHPHQW,IQRWWKHQWKHQH[WHQFORVLQJWU\VWDWHPHQWLVLQVSHFWHGDQGVRRQ,IQRPDWFKLQJLV IRXQGWKHQWKHGHIDXOWH[FHSWLRQKDQGOHUKDOWVWKHSURJUDPDQGSULQWVWKHVWDFNWUDFH 7KHVDPSOHSURJUDPLVJLYHQEHORZ Example 6.6 class ex66 { static void FnA() { try { throw new NullPointerException("demo"); }catch(NullPointerException e) { System.out.println("Caught inside the Function A"); throw e; } } public static void main(String args[]) { try { FnA(); }catch(NullPointerException e) { System.out.println(" Recaught: "+e); } } } The output of the program will be as follows C:\jdk1.2\bin>javac ex66.java C:\jdk1.2\bin>java ex66 Caught inside the Function A Recaught: java.lang.NullPointerException: demo C:\jdk1.2\bin>

Throws

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7KHSURJUDPSURGXFHVDFRPSLODWLRQHUURUOLNHWKLV C:\jdk1.2\bin>javac ex67.java Ex67.java:6: Exception java.lang.IllegalAccessException must be caught, or it must be declared in the throws clause of this method. throw new IllegalAccessException("demo"); ^ 1 error C:\jdk1.2\bin>

7KLVSURJUDPFRXOGEHFRUUHFWHGE\DGGLQJWKHFRGHLQPDLQIXQFWLRQDQGE\DGGLQJWKURZVLQ WKHGHPRIXQFWLRQ class ex67 { static void demo() throws IllegalAccessException { System.out.println("inside the function demo"); throw new IllegalAccessException("demo"); } public static void main(String args[]) { try{ demo(); }catch(IllegalAccessException e) {

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Java Programming I System.out.println("Caught" +e); } } }

7KHRXWSXWRIWKHSURJUDPLVDVIROORZV C:\jdk1.2\bin>javac ex67.java C:\jdk1.2\bin>java ex67 inside the function demo Caughtjava.lang.IllegalAccessException: demo C:\jdk1.2\bin

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Creating Own Exception Subclasses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xample 6.8 class except extends Exception { private int detail; except(int a) { detail=a; } public String toString() { return "My Exception [" + detail + "] "; } } class ex68 { static void compute(int a) throws except { System.out.println("Called compute(" + a + ")"); if(a>10) throw new except(a); System.out.println("Normal exit"); } public static void main(String args[]) { try{ compute(1); compute(20); } catch(except e) { System.out.println("caught " + e); } } }

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Java Programming I

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$QRWKHU([DPSOHWRVKRZWKHZRUNLQJRIXVHUFUHDWHGH[FHSWLRQV Example 6.9 class ex69 { static void FnA() { try{ System.out.println("inside function A"); throw new RuntimeException("demo"); }finally{ System.out.println(" Proc A finally method"); } } static void FnB() { try{ System.out.println("inside function B"); return; }finally{ System.out.println(" Proc B finally method"); } } static void FnC() { try{ System.out.println("inside function C"); }finally{ System.out.println(" Proc C finally method");

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Exception Handling and MultiThreading } } public static void main(String args[]) { try{ FnA(); }catch(Exception e) { System.out.println("Execution Caught "); } FnB(); FnC(); } }

7KHRXWSXWRIWKHSURJUDP C:\jdk1.2\bin>javac ex69.java C:\jdk1.2\bin>java ex69 inside function A Proc A finally method Execution Caught inside function B Proc B finally method inside function C Proc C finally method C:\jdk1.2\bin>

Quick View of Exceptions and their meanings

Exception ArithmeticException ArrayIndexOutOfBoundsException ArrayStoreException ClassCastException IllegalArgumentException IllegalMonitorStateExceptionIllegal IllegalThreadStateException IndexOutOfBoundsException NegativeArraySizeException

Meaning Arithmetic error such as divide by zero. Array index is out of bounds Assignment to an array element of an incompatible type Invalid cast Illegal argument used to invoke a method. monitor operation, such as waiting on an unlocked thread Requested operation not compatible with current thread state Some type of index is out-of bounds. Array created with a negative size

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Java Programming I

Exception NullPointerException NumberFormatException

Meaning Invalid use of a null reference. Invalid conversion of a string to a numeric format

Exception

Meaning

SecurityException ClassNotfoundException CloneNotSupportedException

Attempt to violate security Class not found Attempt to clone an object that does not implement the Cloneable interface Access to a class is denied Attempt to create an object of an abstract class or interface One thread has been interrupted by another thread

IllegalAccessException InstantiationException InterruptedException

MultiThreading Thread

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Exception Handling and MultiThreading

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♦ ♦ ♦ ♦ ♦

Can be created faster Requires less overhead Interprocess communication ids are faster Context switching is faster Uses CPU time optimally. Comp-U-Learn

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Note Java assigns a priority to each thread. A higher priority thread does not run faster than a lower priority thread, if it is the only thread running. Instead a thread’s priority is used to decide when to switch from one running thread to the next. This is called a context switch. 7KH7KUHDGFODVVLPSOHPHQWVWKUHDGVLQ-DYD7KH7KUHDGFODVVLVSDUWRIWKHSDFNDJHMDYDODQJ DQG KHOSV WR LPSOHPHQW -DYD WKUHDGV ZKLFK DUH LQGHSHQGHQW 7KHUH DUH WZR ZD\V WR FUHDWH D FODVVWKDWFDQEHPXOWLWKUHDGHG ♦ Create a class that extends the Thread class ♦ Create a class that implements the Runnable interface. 7KHIROORZLQJDUHWKHWKUHDGVLQ7KUHDGFODVV public thread()

&RQVWUXFWVDQHZWKUHDG7KHWKUHDGPXVWKDYHDUXQPHWKRGDQGDVWDUWPHWKRGWRDFWLYDWHWKH UXQPHWKRG public void run()

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6WDUWVWKHWKUHDG7KLVZLOOFDXVHWKHUXQ PHWKRGWREHFDOOHGDQGUHWXUQLPPHGLDWHO\VRWKDW WKHWKUHDGFDQUXQFRQFXUUHQWO\ public static void sleep(long millesecs)

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Exception Handling and MultiThreading

public static void yield()

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6XVSHQGVDWKUHDG public final void stop()

.LOOVDWKUHDG activeCount()

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Java Programming I

setPriority(int)

6HWVWKHWKUHDGSULRULW\ $QH[DPSOHRIFUHDWLQJWKUHDGXVLQJ7KUHDGFODVVLVVKRZQDVIROORZV Example 6.10 class mythread extends Thread { String name; Thread t; mythread(String s) { t=new Thread(this,s); System.out.println("New thread : " +t); t.start(); } public void run() { try { for(int i=5;i>0;i--) { System.out.println(name + i); Thread.sleep(500); } }catch(InterruptedException e) { } System.out.println(name+ "existing ........"); } } class ex610 { public static void main(String args[]) { mythread m1=new mythread("One"); mythread m2=new mythread("Two"); System.out.println("thread m1 is alive " + m1.t.isAlive()); System.out.println("thread m2 is alive " + m2.t.isAlive()); try{ System.out.println("Waiting ");

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Exception Handling and MultiThreading m1.t.join(); m2.t.join(); }catch(InterruptedException e) { } System.out.println("thread m1 is alive " + m1.t.isAlive()); System.out.println("thread m2 is alive " + m2.t.isAlive()); System.out.println("Existing main thread "); } }

2XWSXWRIWKHSURJUDP C:\jdk1.2\bin>java ex610 New thread : Thread[One,5,main] New thread : Thread[Two,5,main] thread m1 is alive true null5 null5 thread m2 is alive true Waiting null4 null4 null3 null3 null2 null2 null1 null1 nullexisting ........ nullexisting ........ thread m1 is alive false thread m2 is alive false Existing main thread

Comp-U-Learn

137

Java Programming I

Thread States

Runnable

Start( ) or run expires

Dead

Not Runnable Start( )

Stop( ) New Thread Stop( )

New Thread

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Exception Handling and MultiThreading

Not Runnable

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Thread Priority (DFK WKUHDG KDV D SULRULW\ ZKLFK DIIHFWV WKH RUGHU LQ ZKLFK LW LV UXQ 7KUHDGV ZLWK D KLJKHU SULRULW\ VXSHUVHGH WKUHDGV ZLWK D ORZHU SULRULW\ $ WKUHDG LQKHULWV LWV SULRULW\ IURP WKH WKUHDG WKDW FUHDWHG LW 7KH SULRULW\ RI D WKUHDG FDQ EH VHW E\ XVLQJ WKH VHW3ULRULW\ RI WKH 7KUHDG IXQFWLRQ7KHSDUDPHWHUVWRWKLVPHWKRGDUH ♦ MIN_PRIORITY ♦ MAX_PRIORITY ♦ NORM_PRIORITY :KHQPRUHWKDQRQHWKUHDGLVUHDG\IRUH[HFXWLRQ-DYDUXQWLPHV\VWHPFKRRVHVWKHRQHZLWK WKH KLJKHVW SULRULW\ DQG H[HFXWHV LW :KHQ RQH WKUHDG LV EHLQJ H[HFXWHG DQG -DYD HQFRXQWHUV

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139

Java Programming I

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Daemon Threads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xample 6.11 import java.awt.Graphics; import java.util.Date;import java.applet.*; public class time extends Applet implements Runnable { Thread t1; public void start() { if(t1==null) { t1=new Thread(this); t1.start(); } } public void run() { while(t1!=null) { repaint(); try { t1.sleep(1000); } catch(InterruptedException e) { } } } public void paint(Graphics g) { Date d=new Date();

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Exception Handling and MultiThreading g.drawString(d.getHours() +":"+d.getMinutes()+":"+d.getSeconds(),5,10); } public void stop() { t1.stop(); t1=null; } }

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Fig 6.3 $QRWKHUH[DPSOHWRVKRZWKHZRUNLQJRIWKUHDGVXVLQJDSSOLFDWLRQ Example 6.12 class mythread implements Runnable { Thread t; mythread() { t=new Thread(this," Demo Thread"); System.out.println("child thread : " +t); t.start(); } public void run() { try { for(int i=5;i>0;i--) {

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Java Programming I System.out.println("Child Thread : " + i); Thread.sleep(500); } }catch(InterruptedException e) { System.out.println("Child Thread interrupted ."); } System.out.println("Existing child thread "); } } class ex54 { public static void main(String args[]) { new mythread(); try{ for(int i=6;i>0;i--) { System.out.println("Main Thread : " + i); Thread.sleep(1000); } }catch(InterruptedException e) { System.out.println("Main thread Interrupted "); } System.out.println("Existing main thread "); } }

,QVLGHWKHFRQVWUXFWRUP\WKUHDGZHDUHFUHDWLQJDQHZWKUHDGXVLQJWKHVWDWHPHQW T=new Thread(this,”Demo Thread”);

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Exception Handling and MultiThreading Child Thread : 5 Child Thread : 4 Main Thread : 5 Child Thread : 3 Child Thread : 2 Main Thread : 4 Child Thread : 1 Existing child thread Main Thread : 3 Main Thread : 2 Main Thread : 1 Existing main thread C:\jdk1.2\bin>

Summary Exception handling provides a powerful mechanism to control complex programs that have many dynamic run time characteristics. Errors and abnormal situations arising while executing a program needs to be handled. Java provides well-defined methods for exception handling. There are various exception handling classes which are subclasses of Exception. The try, catch ,throw, finally and throws are the keywords involved in exception handling. Multithreading enables the program to make optimum utilization of the available CPU time. It is a feature of the programming environment to make best use of the available resources. Multithreading in Java is offered through Thread class and Runnable interface. The start(), run(), sleep(), stop(), suspend() and resume() are some of the important methods related to threading in Java.

Going Over It Again I. Fill in the Blanks

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143

Java Programming I

II. State True or False

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Session 7

Java Applets

On Completion of this Session We will be able to understand...

) Java Applet ) Applet in Html ) Basic methods of Applet ) Various Applet classes ) Image class in Applet ) Animation in Applet

In This Session...

Introduction to Applet

Applet vs Application

Applet Architecture

Developing an Applet

Applet in HTML

Basic Methods in Applet

Parameter passing to Applets

Graphics Class

Font Class

Color Class

Images

Animation using Images

Java Applets

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Applet vs Application -DYDDSSOLFDWLRQVDUHVLPSOHVWDQGDORQHSURJUDPVWKDWFDQEHUXQE\WKHMDYDLQWHUSUHWHU:HJHW WKH RXWSXW RI WKH DSSOLFDWLRQ SURJUDPV LQ WKH FRPPDQG OLQH RQO\ %XW MDYD DSSOHWV FDQ UXQ LQVLGHWKH:RUOG:LGH:HEEURZVHUDQGZHJHWRXUDSSOHWRXWSXWLQD*8,IRUPDW$SSOHWVFDQ EHORDGHGRYHUWKHQHWZRUNDQGKDYHPRUHFDSDELOLWLHVWKDQWKHMDYDDSSOLFDWLRQSURJUDPV $SDUWIURPWKDWDSSOHWVKDYHWKHIROORZLQJDGYDQWDJHVWKDWQRWHYHQWKHMDYDDSSOLFDWLRQVKDYH 7KH\DUH ♦ Applets have built-in support for multimedia. ♦ Applets running within a Web browser can easily be embedded in a Web page. ♦ Applets can make use of the GUI based pre-defined packages. ♦ Applet provides a frame, event-handling facility and graphics context. ♦ Applets can invoke public methods of other applets on the same page. (YHQWKRXJKWKHDSSOHWVKDYHWKHDERYHIDFLOLWLHVWKH\KDYHKDVVHFXULW\UHVWULFWLRQVWRSUHYHQW WKHPIURPEHLQJDIIHFWHGE\YLUXVHV-DYDDSSOHWVGRHVQ·WVXSSRUWWKHIROORZLQJDVSHFWVGXHWR VHFXULW\UHVWULFWLRQV Comp-U-Learn

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Java Programming I

♦ ♦ ♦ ♦

Applets cannot load libraries or define native methods. An applet cannot ordinarily read or write files on the host that is executing it. An applet cannot make network connections except to the host that it came from. An applet cannot read certain system properties.

Applet Architecture :H KDYH DOUHDG\ VHHQ WKDW DQ DSSOHW LV D VLPSOH MDYD FODVV WKDW XOWLPDWHO\ H[WHQGV WKH MDYDDSSOHW$SSOHWFODVV1RWHWKDWWKHDSSOHWSDFNDJHLVQRWSDUWRIWKH$:7FRPSRQHQW7KH DUFKLWHFWXUHVKRZQLQWKHIROORZLQJILJXUHLOOXVWUDWHVWKLV ,QWKHVXFFHHGLQJVHVVLRQVZHZLOOXVHWKH6ZLQJVHWWRLPSOHPHQWDSSOHWV$OORIWKHDSSOHWVZLOO H[WHQGWKH$SSOHWFODVVWKHVXSHUFODVVIRU6ZLQJDSSOHWV$VZHFDQVHHLQWKHIROORZLQJILJXUH $SSOHWLVDQLPPHGLDWHVXEFODVVRIWKHRUGLQDU\$SSOHWFODVV Object

Component

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Applet

JFrame

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Java Applets

Developing an Applet ,QWKLVVHFWLRQZHDUHJRLQJWROHDUQDERXWWKHFUHDWLRQRIDVLPSOHDSSOHWSURJUDP7KHFUHDWLRQ RIDQDSSOHWFRQVLVWVRIWKHIROORZLQJIRXUVWHSV ♦ ♦ ♦ ♦

Importing the necessary built-in java packages Defining applet subclasses Applet implementation Passing this Java applet’s .class file into HTML file.

&RQVLGHUWKHIROORZLQJDSSOHWH[DPSOHVD\ VDPSOHMDYD ,WLOOXVWUDWHVWKHGHWDLOVWRFUHDWH DQDSSOHW Example 7.1 import java.awt.*; import java.applet.*; public class sample extends Applet { public void paint(Graphics g) { g.drawString("Java Applet Welcomes You!",100,100); } }

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Java Programming I

Fig 7.2 $IWHUFRPSLOLQJRXUMDYDILOHZHFDQDOVRJHWWKHRXWSXWIRUWKHDERYHSURJUDPE\EURZVLQJWKH VDPSOHKWPO ILOH LQ WKH ,QWHUQHW H[SORUHU 7KH IROORZLQJ ILJXUH VKRZV WKH RXWSXW RI WKH VDPSOHSURJUDPLQWKHLQWHUQHWH[SORUHU

Fig 7.3

Note Look at the applet code. There is no main method. Applets don’t need it. The main method is actually in the browser or the appletviewer, not in the Applet itself.

Applet in HTML %HIRUH-DYDZHXVHG+70/WRGHVFULEHWKHOD\RXWRIDZHESDJH+70/LVDVLPSOHYHKLFOHWR LQGLFDWHHOHPHQWVRIDK\SHUWH[WSDJH7KH+70/SDJHPXVWWHOOWKHEURZVHUZKLFKDSSOHWVWR ORDGDQGZKHUHWRSXWHDFKDSSOHWRQWKHZHESDJH7KH$33/(7!DQG$33/(7!WDJV DUHFDOOHG+70/MDYDWDJV7KHMDYDHQDEOHGEURZVHUVZLOOXQGHUVWDQGWKDWFRGHEHWZHHQWKHVH WDJVDUHWKHMDYDFRGH)RUWKDWZLWKLQWKHVHWDJVZHPXVWSDVVWKHIROORZLQJ

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Comp-U-Learn

Java Applets

♦ The name of the class files ♦ The location of the class files ♦ How the applet sits on the web page )RUWKHDERYHUHTXLUHPHQWVWKH$33/(7!WDJKDVWKHIROORZLQJDWWULEXWHV:HFDQXVHWKHVH DWWULEXWHVDFFRUGLQJWRRXUUHTXLUHPHQWV <APPLET>

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