java evolution

8/7/2019 Java Evolution

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Java HistoryJavaJava isis aa generalgeneral purpose,purpose, ObjectObject OrientedOrientedProgrammingProgramming languagelanguage developeddeveloped byby SunSunMicrosystemsMicrosystems ofof USAUSA inin 19911991.. OriginallyOriginally CalledCalled OaKOaKbyby JamesJames Gosling,Gosling, oneone ofof thethe inventorsinventors ofof thethelanguage,language, javajava waswas designeddesigned forfor thethe developmentdevelopmentofof softwaresoftware forfor consumerconsumer electronicelectronic devicesdevices likelikeTVs,TVs, VCRs,VCRs, toasterstoasters andand suchsuch otherother electronicelectronic

machinemachine..TheThe goalgoal hadhad strongstrong impactimpact onon thethe developmentdevelopmentteamteam toto makemake thethe languagelanguage simple,simple, portableportable andandhighlyhighly reliablereliable.


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Java Features

FeaturesFeatures havehave mademade JavaJava thethe firstfirst applicationapplication LanguageLanguage

ofof thethe WorldWorld WideWide WebWeb.. JavaJava willwill alsoalso becomebecome thethepremierpremier languagelanguage forfor generalgeneral purposepurpose standstand--alonealone

applicationsapplications..

Compiled and Interpreted

Usually a Computer language is either compiled or

interpreted, Java combines both these approaches thus

making java a two-stage system. First, Java compiler translates

source code into what is known as bytecode instructions.

Bytecodes are not machine instructions and therefore, in thesecond stage, Java interpreter generates machine code that

can be directly executed by the machine that is running the

Java program. We can thus say that java is both compiled and

an interpreted language.


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Java Features

Platform- Independent and PortableThe Most significant contribution of java over other

languages is its portability. Java programs can be

easily moved from one computer system to another,

anywhere and anytime.

Changes and upgrades in operating systems,

processors and system resources will not force any

changes in java programs.This is the reason why java has become a popular

language for programming on internet which

interconnects different kinds of systems worldwide.


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Java Features

Object OrientedJava is trust object-oriented language.

Almost everything in java is an object. All

program code and data reside withinobjects and classes. Java comes with an

extensive set of Classes, arranged in

packages, that we can use in ourprograms by inheritance. The Object

model in java is simple and easy to

extend.


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Java Features

Robust and SecureJava is robust language. It provides many

safeguards to ensure reliable code. It has

strict compile time and run time checkingfor data types. It is designed as a garbase-

collected language relieving the

programmers virtually all memorymanagement problems.


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Java Features

Distributed

Java is designed as a distributed language

for creating applications on networks. It

has the ability to share both data andprograms. Java application can open and

access remote objects on internet as

easily as they can do in local system. Thisenables multiple programmers at

multiple remote locations to collaborate

and work together on a single project.


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Java Features

Simple, Small and FamiliarJava is small and simple language. Many

features of C and C++ that are either

redundant or sources of unreliable codeare not part of Java.

For Example:- Java does not use Pointers,

preprocessor header files, goto statementand many others.


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Java Features

Multithreaded and InteractiveMultithreaded means handling multiple tasks

simultaneously. Java supports Multithreaded

programs. This means that we need not waitfor the application to finish one task before

beginning another.

For Example:-We can listen to an audio clip while scrolling a

page and at the same time download applet

from a distant computer


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Java Features

High Performance

Java performance is impressive for an

interpreted language, mainly due to theuse of intermediate bytecodde.

According to SUN. Java speed is

comparable to the native C/C++.Java architecture is also designed to

reduce overheads during runtime.


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Java Features

Dynamic and Extensible

Java is dynamic language. Java is capable of

dynamically linking in new class libraries,

methods, and objects. Java can also determine

the type of class through a query, making it

possible to either dynamically link of abort the

program, depending on the response.Java programs support functions written in

other language such as C, C++. These function

are known as native methods.


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Differs From C and C++

Java was modeled after C and C++

languages. It differs from C and C++ in

many ways. Java does not incorporate anumber of features available in C and

C++. For the benefit of C and C++

programmers, we point out here a fewmajor differences between C/C++ and

java languages.


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Java is lot like C but the major difference

between Java and C is that Java is an

Object-Oriented Language and hasmechanism to define classes and objects.

Java does not include the C uniquestatement keywords, sizeof, and

typedef.

Java and CJava and C


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Java does not contain the data typesStruct and union

Java does not define the type modifiers

keywords auto, extern, register, signed,and unsigned.

Java does not support an explicit Pointer

type Java does not have preprocessor and

therefore we can not use #define,

#include



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Java requires that the functions with noarguments must be declared with empty

parenthesis and not with the void

keywords as done in C. Java add new operators such as

instanceof and >>>

Java adds labelled break and continue

statements.



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Java is true Object Oriented Languagewhile C++ is basically C with Object

Oriented Extension. That is what exactly

the increment operator ++ indicates.C++ maintained backward compatibility

with C. it is therefore possible to write an

old style C program and run itsuccessfully under C++. Java appears to

be similar to C++ when we consider only

the Extension part of C++

Java and C++Java and C++


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Listed below are some major C++ features that wereintentionally omitted from java of significantly Modified.

Java does not support Operator

Overloading.

Java does not have template classes as in

C++

Java does not support multipleinheritance of classes. This is

accomplished using a new feature called

Interface



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Java does not support GlobalVariables. Every variable and method

is declared within a class and forms

part of the class.

Java does not use pointers.

Java has replaced the destructorfunction with a finalize() function.

There are no header files in Java.



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Overlapping of C, C++, and JavaOverlapping of C, C++, and Java

CC

C++C++

JAVAJAVA


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Java is strongly associated with theInternet because of the fact that the

first application program written in

Java was HotJava, a web browser to

run applets on Internet. Internet user

can use Java to create applet

programs and run them locally using

a Java enabled Browser such as

HotJava.

Java and InternetJava and Internet


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Java environment includes a largenumber of development tools and

hundreds of classes and methods. The

development tools are part of the systemknown as Java Development Kit(JDK) and

the classes and the method are part of

the Java Standard Library(JSL), alsoknown as the Application Programming

Interface(API).

Java EnvironmentJava Environment


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TheThe JavaJava DevelopmentDevelopment KitKit comescomes withwith aa collectioncollection ofof toolstools thatthatareare usedused forfor developingdeveloping andand runningrunning javajava programsprograms.. ThenThen

includeinclude::

Appletviewer(for viewing java applet)

Javac (Java compiler)

Java (Java Interpreter)

Javap (Java disassembler)

Javah (For C header file)

Javadoc (For creating HTML Document)

Jdb (Java debugger)

Java Development Kit (JDK)Java Development Kit (JDK)


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JavaJava isis generalgeneral purposepurpose ObjectObjectOrientedOriented ProgrammingProgramming LanguageLanguage..

WeWe cancan developdevelop twotwo typestypes ofof javajava

programsprograms..

StandStand alonealone applicationapplication WebWeb AppletsApplets

IntroductionIntroduction


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Two ways of using JavaTwo ways of using JavaJava

Soruce

Code

Java

Compiler

JavaEnabled

Web

Browser

Java

Interpreter

Output Output

Applet TypeApplet Type Application TypeApplication Type


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U

seJ

DK 1.5 version.U

seJ

DK 1.5 version.Environment Variable.Environment Variable.

Variable Name:Variable Name: ClasspathClasspath

value:value: bin;lib;Cbin;lib;C:;D:;:;D:;Variable Name:Variable Name: javahomejavahome

value:value: bin;libbin;lib;;

Variable Name: pathVariable Name: pathvalue:value: bin;libbin;lib;;

Installation & Environment Variable SettingInstallation & Environment Variable Setting


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classclass SampleOneSampleOne

{{

publicpublic StaticStatic voidvoid main(Stringmain(String argsargs [])[])

{{

SystemSystem..outout..println(Javaprintln(Java isis betterbetter thanthan C++C++..));;

}}}}

Simple Java ProgramSimple Java Program


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import java.lang.Math;

classclass SampleOneSampleOne

{{

publicpublic StaticStatic voidvoid main(Stringmain(String argsargs [])[])

{{

doubledouble x=x=55;; //declaration//declaration andand initializationinitialization

doubledouble yy;;

y=y= MathMath..sqrt(x)sqrt(x);;

SystemSystem..outout..println(y=println(y= +y)+y);;

}}

}}

A Java Program with multiple statementA Java Program with multiple statement


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ImplementationImplementation ofof aa javajava applicationapplication programprogram

involvesinvolves aa seriesseries ofof stepssteps.. TheyThey includeinclude

CreatingCreating aa programprogram

CompilingCompiling thethe programprogram

RunningRunning thethe programprogram

RememberRemember that,that, beforebefore wewe beginbegin creatingcreating thethe

program,program, thethe javajava DevelopmentDevelopment KitKit (JDK)(JDK) mustmust

bebe properlyproperly installedinstalled onon ourour systemsystem..

Implementing a Java ProgramImplementing a Java Program


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classclass TestTest

{{

publicpublic staticstatic voidvoid main(Stringmain(String args[])args[])

{{

SystemSystem..outout..println(println(hellowhellow!)!);;

SystemSystem..outout..println(Welcomeprintln(Welcome toto thethe worldworld ofof java)java);;

SystemSystem..outout..println(Letprintln(Let usus LearnLearn Java)Java);;

}}

}}

Another simple program for testingAnother simple program for testing


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To Compile the program, we must run the javacompiler javac, with name of the source file on

the command line as shown below.

CC::/>/>javacjavacTestTest..javajava

ifif everyevery thinkthink ok,ok, thethe javacjavac compilercompiler createscreates aa filefile

calledcalled TestTest..classclass containingcontaining thethe bytecodesbytecodes ofof thethe

programprogram.. NoteNote thatthat thethe compilercompiler automaticallyautomatically

namesnames thethe bytecodebytecode filefile asas .. ClassClass

TestTest..classclass

Compiling the programCompiling the program


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We need to use the java interpreter to run astand-alone program. At the command prompt,

type

CC::/>java/>java TestTest

NowNow thethe interpreterinterpreter lookslooks forfor thethe mainmain methodmethod inin thethe

programprogram andand beginsbegins executionexecution fromfrom therethere.. WhenWhen

executed,executed, ourour programprogram displaysdisplays thethe followingfollowing::

HellowHellow!!WelcomeWelcome toto thethe worldworld ofofJavaJava

LetLet usus LearnLearn JavaJava

Running the programRunning the program


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All language compilers translate sourcecode into machine code for a specific

computer. Java compiler produces an

intermediate code known as byte code fora machine that does not exist. This

machine is called the Java Virtual Machine

and it exists only inside the computermemory.

Java Virtual Machine (JVM)Java Virtual Machine (JVM)

Java

Program

Java

Compiler

Virtual

Machine


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Command line arguments are the

parameters that are supplied to

the application program at time ofinvoking it for execution. These are

passed as parameters to the

main() function.

Command line argumentsCommand line arguments


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Command line argumentsCommand line argumentsclass ComLine

{Public static void main(String args[])

{

Int count, i=0;

String string ;count =args.length; //Property of String array

System.out.println(Number of Arguments= +count);

While(i


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Class add

{

public static void main (String args[])

{Double a=10,b=20;

System.out.println(Addition= +(a+b));

}}


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public class evenOdd

{

public static void main(String args[]){

int num=10;

if(num%2!=0)

{ System.out.println(num+ is Odd.);

}

else

{ System.out.println(num+ is Even.);

}

}

}


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class areaCircle

{

public static void main(String args[])

{

double r=10;final double PI=3.14; //Constant

System.out.println(Area= +(PI*r*r));

}

}


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class SimpleInterest

{


{

double p=1500, r=10, t=4;System.out.println(SI= +(p*r*t)/100);

}

}


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class power

{


{

int b=4, p=3;int res=Math.pow(b , p );

System.out.println(b+ power +p+ = +res)

}

}


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class table5

{


{

int i, num=5;for(i =1;i


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class CountEven

{


int count=0;

for( i =1;i


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class Printsequence

{

public static void main(String args[]) {

int i=1 ,n=1;

char ch=a;

while(i


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VariablesAA variablevariable isis anan identifieridentifier thatthat

denotesdenotes aa storagestorage locationlocation usedused toto

storestore aa datadata valuevalue.. UnlikeUnlike

constantsconstants thatthat remainremain unchangedunchangedduringduring thethe executionexecution ofof aa

program,program, aa variablevariable maymay taketake

differentdifferent valuesvalues atat differentdifferent timestimes

duringduring thethe executionexecution ofof thethe

programprogram..


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Data Types

E

veryE

very variablevariable inin javajava ofof aadatadata typetype.. DataData typetype

specifyspecify thethe sizesize andand typetype ofofvaluesvalues thatthat cancan bebe storedstored..

JavaJava languagelanguage isis richrich inin itsits

datadata typetype..


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Data Types

in JAVA

Primitive

(Intrinsic)

Non-Primitive

(Derived)

Numeric Non-numeric Classes Arrays

Interface

IntegerFloating

Point Character Boolean

Data Types in Java

Note: Boolean Data type Value is TRUE or FALSENote: Boolean Data type Value is TRUE or FALSE

but Default Value is FALSEbut Default Value is FALSE


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Integer TypesJavaJava supportssupports fourfour typestypes ofof

integersintegers areare byte,byte, short,short, int,int,

andand longlong.. JavaJava doesdoes notnot

supportsupport thethe conceptconcept ofofunsignedunsigned typestypes andand thereforetherefore

allall javajava valuesvalues areare signedsignedmeaningmeaning theythey cancan bebe positivepositive

oror negativenegative..


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Size and Range of Integer Types

Type Size Minimum value Maximum Value

Byte One Byte -128 127

Short Two bytes -32,768 32,767

int Four bytes -2,147, 483, 648 2, 147, 483, 647

long Eight bytes -9, 223, 372, 036,

854, 775, 808

9, 223, 372, 036,

854, 775, 807


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Floating Point Types

IntegerInteger typestypes cancan holdhold onlyonlywholewhole numbersnumbers andand

thereforetherefore wewe useuse anotheranothertypetype knownknown asas ((floatingfloating

pointpoint constant)constant)..


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Floating

Point

Float Double

Floating point data types

Type Size Minimum Value Maximum Value

Float 4 Bytes 3.4e-038 3.4e+038

Double 8 Bytes 1.7e-308 1.7e+308

Size and Range of Floating Point Types


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Character TypeInIn javajava thethe datadata typetype usedused toto storestore charactercharacter isis

charchar.. HoweverHowever C,C, C++C++ programmersprogrammers bewarebeware:: charcharinin javajava isis notnot thethe samesame asas charchar inin C,C, C++C++.. InIn

C/C++,C/C++, CharChar isis anan integerinteger typetype thatthat isis 88 bitsbits ((11

Byte)Byte) widewide.. ThisThis isis notnot thethe casecase inin javajava.. Instead,Instead,javajava usesuses UnicodeUnicode toto representrepresent characterscharacters foundfound

inin allall humanhuman languageslanguages.. InIn javajava charactercharacter isis aa 1616--

bitbit typetype.. TheThe rangerange ofof charchar isis 00 toto 6565,,536536.. therethere

areare nono negativenegative charschars.. TheThe standardstandard setset ofof

charactercharacter knownknown asas ASCIIASCII stillstill rangerange fromfrom 00 toto

127127 asas always,always, andand thethe extendedextended 88--bitbit charactercharacter

set,set, ISOISO--LatinLatin--11,, rangesranges fromfrom 00 toto 255255..

//D h d


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//Demonstrate char data type.

Class CharDemo

{


{

char ch1, ch2;

ch1=8; //code for Xch2=Y;

System.out.print(Ch1 and ch2: );

System.out.println(ch1+ +ch2);

}

}


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Boolean Type

BooleanBoolean TypeType isis usedused whenwhen wewewantwant toto testtest aa particularparticular

conditioncondition duringduring thethe executionexecutionofof thethe programprogram.. ThereThere areare onlyonly

twotwo valuesvalues thatthat aa BooleanBoolean typetypecancan taketake:: TRUETRUE oror FALSEFALSE..

DefaultDefault valuevalue isis FALSEFALSE..

//Demonstrate Boolean values


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//Demonstrate Boolean values.

Class BoolTest

{


{

b=false;

System.out.println(b is +b);

b=true;

System.out.println(b is +b);// a boolean value can control the if statement

if(b) System.out.println(This is executed.);

b=false;

if(b) System.out.println(This is not executed.);

//outcome of a relational operator is a boolean value

System.out.println(10>9 is +(10>9));

}

}


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Standard Default Values

Type of Variable Default Value

Byte Zero : (byte) 0

Short Zero : (Short) 0

Int Zero: 0

Long Zero:0L

Float 0.0f Char Null Character

Boolean False

Reference null

In Java, every variable has a default value. If we dontinitialize a variable when it is first created, java providesdefault value to that variable.


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LabelledLoops

InIn java,java, wewe cancan givegive aa labellabel toto aablockblock ofof statementsstatements.. AA labellabel isis

anyany validvalid javajava variablevariable namename.. totogivegive aa labellabel toto aa loop,loop, placeplace itit

beforebefore thethe looploop withwith aa coloncolon atatthethe endend..

class cb


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class cb

{

public static void main(String args[]) {

LOOP1: for(int i=1;i=10) break;

for(int j=1; j


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Arrays, Strings and Vectors

AnAn arrayarray isis aa groupgroup ofof contiguouscontiguous ororrelatedrelated datadata itemsitems thatthat shareshare aa

commoncommon namename..

OneOne DimensionalDimensionalarraysarrays

TwoTwo DimensionalDimensionalarraysarrays

MultiMulti DimensionalDimensionalarraysarrays

AnonymousAnonymous ArrayArray


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Creating anArray

LikeLike anyany otherother variables,variables, arraysarrays mustmust bebedeclareddeclared andand createdcreated inin thethe computercomputer

memorymemory beforebefore theythey areare usedused.. CreationCreation ofof

anan arrayarray involvesinvolves threethree stepssteps.. DeclaringDeclaring thethe arrayarray

CreatingCreating MemoryMemory locationslocations

PuttingPutting valuesvalues intointo thethe memorymemory locationslocations


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Declaration ofArrays

ArraysArrays inin JavaJava maymay bebe declareddeclared inin twotwo waysways..

FormForm11

FormForm11

ExamplesExamples::

intint number[number[ ]];;

floatfloat average[average[ ]];;

intint [[ ]=]= countercounter;;

float[float[ ]=marks]=marks;;

Type arrayname[ ];

Type [ ]arrayname;

Remember, we do not enter

the size of the arrays in thedeclaration


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Creation ofArrays

AfterAfter declaringdeclaring anan array,array, wewe needneed toto createcreate itit inin thethememorymemory.. JavaJava allowsallows usus toto createcreate arraysarrays usingusing newnew

operatoroperator only,only,

ExamplesExamples::

numbernumber == newnew int[int[55]];;

averageaverage == newnew float[float[1010]];;

TheseThese lineslines createcreate necessarynecessary memorymemory locationslocations forfor thethe arraysarraysnumbernumber andand averageaverage andand designatedesignate themthem asas intint andand floatfloat

respectivelyrespectively.. Now,Now, thethe variablevariable numbernumber refersrefers toto anan arrayarray ofof 55

integersintegers andand averageaverage refersrefers toto anan arrayarray ofof 1010 floatingfloating pointpoint

valuesvalues..

Arrayname=new type [size];


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ItIt isis alsoalso possiblepossible toto combinecombine thethe twotwo stepssteps-- declarationdeclaration

andand creationcreation-- intointo oneone asas shownshown belowbelow..

StatementStatement ResultResult

intint numbernumber [][];;

Number=newNumber=new intint [[55]];;

int number[ ]=new int [5];

PointsPoints nowherenowhere

NumberNumber [[00]]

NumberNumber [[11]]

NumberNumber [[22]]

NumberNumber [[33]]

NumberNumber [[44]]

f


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Initialization ofArrays

TheThe FinalFinal stepstep isis toto putput valuesvalues intointo thethe arrayarray createdcreated..ThisThis processprocess isis knownknown asas initializationinitialization..

ExamplesExamples::intint number[number[ ]={]={3535,, 4040,, 2020,, 5757,, 1919}};;

ItIt isis possiblepossible toto assignassign anan arrayarray objectobject toto anotheranother.. ExampleExample::

intint a[a[ ]=]= {{11,, 22,, 33}};;

intint b[b[ ]];;b=ab=a;;

AreAre validvalid inin javajava.. BothBoth thethe arraysarrays willwill havehave thethe samesame valuesvalues..

Arrayname[ subscript]=value

A h


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Array length

InIn java,java, allall arraysarrays storestore thethe allocatedallocatedsizesize inin aa variablevariable namednamed lengthlength.. WeWe

cancan obtainobtain thethe lengthlength ofof thethe arrayarray aa

usingusing aa..lengthlength..

intint aSize=aSize= aa..lengthlength;;

ThisThis informationinformation willwill bebe usefuluseful inin thethemanipulationmanipulation ofof arraysarrays whenwhen theirtheir

sizessizes areare notnot knownknown..

//Average an array of values


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//Average an array of values.

Class Average

{


{

double nums[ ]={10.1, 11.2, 12.3, 13.4, 14.5};

double result=0;

int i;

for(i=0;i


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Two dimensionalArrayTwoTwo dimensionaldimensional arraysarrays areare storedstored inin memorymemory asas withwith

thethe singlesingle dimensionaldimensional arrays,arrays, eacheach dimensiondimension ofof thethearrayarray isis indexedindexed fromfrom zerozero toto itsits maximummaximum sizesize

minusminus oneone;; thethe firstfirst indexindex selectsselects thethe rowrow andand thethe

secondsecond indexindex selectsselects thethe columncolumn withinwithin thatthat rowrow..

For creating two-dimensional arrays, we must follow the same

steps as that of simple arrays. We may create a two-

dimensional array like this.

int myArray[ ][ ];

myArray=new int [3][4];

Or

int myArray[ ][ ]=new int[3][4];

//Demonstrate a two-dimensional array.

O t t


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Class TwoDArray

{


{intTwoD[ ][ ]=new int [4][5];

int i, j, k=0;

for(i =0;i


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//Manually Allocate differing size second dimensions

Class TwoDAgain

{public static void main(String args[])

{

intTwoD[ ][ ]=new int [4][ ];TwoD[ 0]=new int [1 ];

TwoD[ 1]=new int [2 ];



int i, j, k=0;

To be Continue..O t t


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To be Continue..

int i, j, k=0;

for(i =0;i


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// y

Class threeDMatrix

{


int threeD[ ][ ][ ]=new int [3][4][5];

int i,j,k;

for( i =0;i


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for( i =0;i


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Anonymous Array

In java it is perfectly legal to create an anonymousIn java it is perfectly legal to create an anonymous

array using the following syntax.array using the following syntax.

new [] { };

Anonymous array exampleAnonymous array example

new int[]{1,2,3};

The above given example creates a nameless array and

initializes it. Here, neither name of the array nor the

size is specified. It also creates a array which can be

assigned to reference or can be passed as a parameter

to any method.

//Anonymous array program


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// y y p g

public AnonymousArrayExample{

public static void main(String args[]){System.out.println(Length of array is + findLength(new int[]{1,2,3}));

}

public static findLength(int[] array){

return array.lentgh;

}

}

The above given program will print the length of theThe above given program will print the length of the

anonymous array which is being passed to the staticanonymous array which is being passed to the static

method.method.

ForFor--each Loopeach Loop


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ForFor--each Loopeach LoopPurposePurpose

The basic for loop was extended in Java 5 to makeiteration over arrays and other collections more

convenient. This newer for statement is called the

enhanced foror for-each (because it is called this in other

programming languages).The for-each loop is used to access each successive value

in a collection of values.

Arrays and Collections.Arrays and Collections.

It's commonly used to iterate over an array or a

Collections class (eg, ArrayList).

General FormGeneral Form


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GeneralFormGeneralForm

The for-each and equivalent forstatements have these forms.

For-each loop Equivalent for loop

for (type var: arr)

{

body-of-loop

}

for (int i= 0; i < arr.length; i++)

{

type var= arr[i];

body-of-loop}

for (type var: coll)

{

body-of-loop

}

for (Iterator iter= coll.iterator();

iter.hasNext(); )

{

type var= iter.next();body-of-loop

}

//For Each loop with anonymous Array//For Each loop with anonymous Array


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//For Each loop with anonymous Array//For Each loop with anonymous Array

public class MainClass

{public static void main (String args[])

{

int array1[] = {1, 2, 3, 4, 5};

for(int i: array1){

System.out.println(i);

}

}

}

St i


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StringIn Java a string is a sequence of characters , but,

unlike many other languages that implement string ascharacter arrays, java implements strings as objects

of the String class.

In java string are class objects and implemented

using two classes, namely, String and StringBuffer. A

java string is an instantiated object of the String

Class. Java Strings, as compared to C strings, are more

reliable and predictable. This is basically due to Cs

lack of bounds-checking. A java String not a

character array and is not NULL terminated.

Th t i l d St i B ff d fi d


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The string class and StringBuffer are defined

in java.lang. thus, they are available to all

programs automatically.The String Constructors

The String class support several constructors.

To create an empty String, you call the

default constructor.

Example:

String s=new String();// will create an instance of String

with no character with it.

Syntax:


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Syntax:

String stringname;

StringName=new String(String);Example:

String firstName;

firstName =new String(JAVA);

These Two Statements may be combinedas follows:

String firstName =new String(Java);

Note the use of parentheses here. Java strings can be

concatenated using the + operator.String fullName=name1+name2;

String city1=New+Delhi;

System.out.println(firstName+Kumar);

//Construct one String from another


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Class MakeString


{

char c[ ]={J, A, V, A};String s1=new String(c);

String s2=new String(s1);

System.out.println(s1);System.out.println(s2);

}

}

Output:

Java

Java

//Construct string from subset of char array.


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Class SubStringCons

{

public static void main (String args[]){

byte ascii[ ]={65,66,67,68,69,70};

String s1=new String (ascii);

System.out.println(s1);String s2=new String(ascii,2,3);

System.out.println(s2);

}

}

Output:

ABCDEF

CDE

HERE, asciiChars specifies the array of bytes. The second form

allows you to specify a subrange. In each of these constructors,

the byte-to-character conversion is done by using the default

character encoding of the flateform.

Note about String


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Note about String

TheThe ContentsContents ofof thethe arrayarray areare copiedcopied wheneverwhenever youyou createcreate aaStringString objectobject fromfrom anan arrayarray.. IfIf youyou modifymodify thethe contentscontents ofof thethe

arrayarray afterafter youyou havehave createcreate thethe string,string, thethe StringString willwill bebe changedchanged..

StringString LengthLength

TheThe lengthlength ofof aa stringstring isis thethe numbernumber ofof characterscharacters thatthat ititcontainscontains.. ToTo obtainobtain thisthis valuevalue callcall thethe length()length() methodmethod..

charchar chars[]={a,chars[]={a, b,b, c}c};;

StringString s=news=new String(chars)String(chars);;SystemSystem..outout..println(println( ss..length())length());;

String Methods


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String MethodsTheThe StringString classclass definesdefines aa numbernumber ofof methodsmethods thatthat allowallow usus toto

accomplishaccomplish aa varietyvariety ofof stringstring manipulationmanipulation taskstasks.. ListsLists somesome ofof

thethe mostmost commonlycommonly usedused stringstring methodsmethods andand theirtheir taskstasks;;

Method Call Task performed

S2=s1.toLowerCase; Converts the string s1 to all lowercase

S2=s1.toUpperCase; Converts the string s1 to all Uppercase

S2=s1.replace(x, y); Replace all appearances of x with y

S2= s1.trim(); Remove White Spaces at the beginning

and end of the string s1

S1.equals(s2); Returns True if s1 is equal to s2.

S1.equalsIgnoreCase(s2); Returns True if s1=s2, ignoring the case

of characters

S1.length; Gives the length of s1

String Methods


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String MethodsMethod Call Task performed

S1.charAt(n) Gives the nth character of s1

S1.compareTo(s2); Returns negative if s1s2, and zero if s1 is equal s2.

S1.concate(s2); Concatenates s1 and s2

S1.substring(n); Gives substring starting from nth

character

S1.substring(m, n); Gives substring starting from nth

character up to mth (Not including mth)

S1.indexOf(x) Gives the position of the first occurrence

of x in the String s1

S1.indexOf(x, n) Gives the position of x that occurs after

nth position in the String s1

StringBuffer Class


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StringBufferClassStringBufferStringBuffer isis aa peerpeer classclass ofof StringString.. WhileWhile StringString createscreates

stringsstrings ofof fixed_lengthfixed_length,, StringBufferStringBuffer createscreates stringsstrings ofof flexibleflexible

lengthlength thatthat cancan bebe modifiedmodified inin termsterms ofof bothboth lengthlength andand contentcontent..

CommonlyCommonly usedused StringBufferStringBuffer methodsmethods

Method Tasks

S1.setCharAt(n, x) Modifies the nth character to x

S1.append(s2) Appends the string s2 to s1 at the end

S1.insert(n,s2) Inserts the string s2 at the position n of the

string s1

S1.SetLength(n) Sets the length of the string s1 to n. if

ns1.length() zeros are added to s1

//Manipulation of string

l l


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Class StringManipulation

{

public static void main (String args[]){

StringBuffer str= new StringBuffer(Object Language);

System.out.println(Original String:+str);

//obtaining String Length//obtaining String LengthSystem.out.println(Length of String:+str.length());

//Accessing Character in a String//Accessing Character in a String

for(int i=0; i


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//Inserting a string in the middle

String aString=new String(str.toString());

int pos=aString.indexOf( language);str.insert(pos, Oriented );

System.out.println(Modified string : +str);

//Modifying Characters

Str.setCharAt(6, -);System.out.println(String Now: +str);

//Appending a string at the end

Str.append( improves security. );

System.out.println(Appended string:+str);

}

}

//Alphpabetical Ordering of Strings

class StringOrdering


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class StringOrdering

{

static String name[]={Madras, Delhi,

Ahmedabad,Calcutta,Bombay};

public static void main (String args[ ])

{

int size=name.length;

String temp=null;

for(int i=0;i


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VectorUseUse ofof thethe VectorVector ClassClass containedcontained inin thethe javajava..utilutil

packagepackage.. ThisThis classclass cancan bebe usedused toto createcreate aagenericgeneric dynamicdynamic arrayarray knownknown asas vectorvector thatthat cancan

holdhold objectsobjects ofof anyany typetype andand numbernumber.. ArraysArrays

cancan bebe implementedimplemented asas vectorvector.. VectorsVectors areare

createdcreated likelike arraysarrays asas followsfollows..

vectorvector intVectintVect == newnew vector()vector();;

//declare//declare withoutwithout sizesize

vectorvector list=newlist=new vector(vector(33));;

//// declaringdeclaring withwith sizesize

Vectors Advantages over arrays


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VectorsAdvantages over arrays11.. ItIt isis convenientconvenient aa numbernumber ofof advantagesadvantages overover

arrayarray..22.. AA vectorvector cancan bebe usedused toto storestore aa listlist ofof objectsobjects

thatthat maymay varyvary inin sizesize..

33.. WeWe cancan addadd deletedelete objectsobjects fromfrom thethe listlist asasandand whenwhen requiredrequired..

AA majormajor constraintconstraint inin usingusing vectorsvectors isis thatthat wewe

cancan notnot directlydirectly storestore simplesimple datadata typetype inin aa

vectorvector;; wewe cancan onlyonly storestore objectsobjects.. Therefore,Therefore, wewe

needneed toto convertconvert simplesimple typestypes toto objectsobjects.. ThisThis cancan

usingusing withwith wrapperwrapper classclass..

Vector Methods


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Vector Methods

Method Tasks

list.addElement(item) Adds the item specified to the list at the end

list.elementAt(10) Gives the name of the 10th objects

list.size() Gives the number of objects present

list.removeElement(item) Removes the specified item from the list

list.removeElementAt(n) Removes the item stored in the nth position

of the list

list.removeAllElements( ) Removes all the elements in the list.

list.copyInto(array) Copies all items from list to array

List.insertElementAt(Item, n) Insert the item a nth position

//Program illustrates the use of arrays, string and vectors. This


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program converts a string vector into an array of strings and

displays the strings.

import java.util.*; //importing vector classclass languageVector

{


{

Vector list =new Vector();

int length=args.length;

for(int i=0;i


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list.insertElementAt( COBOL , 2);

int size=list.size();

String listArray[]=new String[size];list.copyInto(listArray);

System.out.println(List of languages);

for(int i=0;i


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WrapperClasses

AsAs pointedpointed outout earlier,earlier, vectorsvectors

cannotcannot handlehandle primitiveprimitive datadata typestypeslikelike int,int, float,float, long,long, charchar andand

doubledouble.. PrimitivePrimitive datadata typestypes maymaybebe convertedconverted intointo objectobject typestypes byby

usingusing thethe wrapperwrapper classesclasses

containedcontained inin thethe javajava..langlangpackagepackage..

Wrapper Classes for Converting Simple Types


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WrapperClasses forConverting Simple Types

Simple Type Wrapper Class

boolean boolean

Char Character

double Double

float Float

int Integer

long Long

The wrapper classeshave a number of uniquemethods

f h dli i i i d d bj Th


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forhandling primitive data types and objects. There are

listed in the following tables.

Converting PrimitiveNumbers to objectsNumber using

Constructormethods

Constructor Calling Conversion Action

Integer IntVal=new Integer(i); Primitive integer to integer object

Float FloatVal= new Float(f); Primitive Float to Float object

Double DoubleVal=newDouble(d) Primitive Double to Double object

Long LongVal=new Long(l); Primitive long to long object

Note: i, f, d and l are primitive data values denoting int,

float, double, and long data types. They may be

constants or variables.

Converting Object Numbers to Primitive Numbers


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Converting ObjectNumbers to PrimitiveNumbers

using typeValue()method

Method Calling Conversion Action

Int i=intVal.intValue(); Object to primitive integer

Float f=FloatVal.floatValue() Object to primitive float

Long l=longVal.longValue(); Object to primitive long

Double d= DoubleVal.DoubleValue(); Object to primitive Double




C ti N b t St i U i t St i () M th d


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ConvertingNumbers to Strings Using to String() Method


Str=Integer.toString(i) Primitive integer to string

Str=Float.toString(f) Primitive float to string

Str=Double.toString(d) Primitive double to string

Str=Long.toString(l) Primitive long to string




Converting String Objects toNumeric Objects Using the


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C e g S g O jec s e c O jec s Us g e

Static Method ValueOf()


DoubleVal=Double.Valueof(str); Converts string to Double objects

FloatVal=Float.ValueOf(str); Converts string to Float object

IntVal=Integer.Valueof(str); Converts string to integer object

LongVal=Long.ValueOf(str); Converts string to Long object

ConvertingNumeric Strings to PrimitiveNumbers Using


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g g g

Parsing Methods


Int =Integer.parseInt(str); Converts string to primitive integer

long i=Long.parseLong(str); Converts string to primitive long

parseInt() and parseLong( )methods throw a numberformatException if the value of the str does not

represent an integer.

//Use of wrapper class methods


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import java.io.*;

class Invest

{


{

float principalAmount=newFloat(0); //Converting number to object

float intrestRate=new float(0);

int numYears=0;

try

{

DataInputStream in=new DataInputStream(System.in);

System.out.print(Enter Principal Amount:);

System.out.flush();

String principalString=in.readLine();

principalAmount=Float.valueOf(principalString);


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// String object to number object

System.out.print(EnterInterest Rate:);

System.out.flush();

String interestString=in.readLine();

interestRate=Float.valueOf(interestString);

System.out.print(Enter Number Of Years:);

System.out.flush();

String yearsString=in.readLine();

numYears=Integer.parseInt(yearsString); //Numeric strings to numbers

} //Try brace closing

Catch (IOException e) //Exception Handling

{

System.out.println(I/O Error);

System.exit(1);

}

Float value=loan(principalAmount.floatvalue(),interestRate.floatValue(),

numYears);


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numYears);

printline();

System.out.println(final Value=+value);

Printline();

} //main function closing Brace

static float loan(float p, float r, int n) //User definedFunction

{

int year=1;float sum=p;

while(year


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Co pos te atatypesTheThe datatypedatatype thatthat areare basedbased onon

fundamentalfundamental oror primitiveprimitive datatypes,datatypes, areareknownknown asas CompositeComposite DatatypesDatatypes.. SinceSince

thesethese datatypesdatatypes areare createdcreated byby users,users, thesethese

areare alsoalso knownknown asas UserUser--DefinedDefined DatatypesDatatypes..ClassClass::--

sincesince thesethese datatypesdatatypes areare createdcreated

throughthrough classes,classes, wewe shallshall bebe exploringexploringhowhow classesclasses formform thethe platformsplatforms forfor

creatingcreating useruser--defineddefinedtypestypes..

Defining aClass

AA ll ii d fi dd fi d dd i hi h


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AA classclass isis aa useruser defineddefined datadata typetype withwith aa

templatetemplate thatthat servesserves toto definedefine itsits propertiesproperties..

syntaxsyntax::

classclass class_nameclass_name

{{

datadata membermember;;

membermember functionfunction;;

}}

OnceOnce thethe classclass typetype hashas beenbeen defined,defined, wewe cancan createdcreatedvariablesvariables ofof thatthat typetype usingusing declarationsdeclarations thatthat areare

similarsimilar toto thethe basicbasic declarationsdeclarations.. InIn java,java, thesethese

variablesvariables areare termedtermed asas instancesinstances ofof classes,classes, whichwhich areare

thethe actualactual objectobject..

JavaAccess Specifier

AA M difiM difi


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AccessAccess ModifiersModifiers

oo

PrivatePrivateoo ProtectedProtected

oo DefaultDefault

oo PublicPublicPublicPublic accessaccess modifiermodifier::-- Fields,Fields, methodsmethods andand

constructorsconstructors declareddeclared publicpublic (least(least restrictive)restrictive)

withinwithin aa publicpublic classclass areare visiblevisible toto anyany classclass ininthethe javajava program,program, whetherwhether thesethese classesclasses areare inin

thethe samesame packagepackage oror inin anotheranother packagepackage..



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PrivatePrivate accessaccess modifiermodifier::-- thethe privateprivate (most(most

restrictive)restrictive) fieldsfields oror methodsmethods cannotcannot bebe usedused forfor

classesclasses andand interfacesinterfaces.. Fields,Fields, methodsmethods oror

constructorsconstructors declareddeclared privateprivate areare strictlystrictly

controlled,controlled, whichwhich meansmeans theythey cannotcannot bebe accessesaccesses

byby anywhereanywhere outsideoutside thethe enclosingenclosing classclass..NoteNote::--

AA standardstandard designdesign strategystrategy isis toto makemake allall

fieldsfields privateprivate andand provideprovide publicpublic gettergettermethodsmethods forfor themthem..



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protectedprotected accessaccess modifiermodifier::-- TThehe protectedprotected

fieldsfields oror methodsmethods cannotcannot bebe usedused forfor classesclasses andand

interfacesinterfaces.. ItIt alsoalso cannotcannot bebe usedused forfor fieldsfields andand

methodsmethods withinwithin anan interfaceinterface.. Fields,Fields, methodsmethods

andand constructorsconstructors declareddeclared protectedprotected inin aa

superclasssuperclass cancan bebe accessedaccessed onlyonly byby subclassessubclasses ininotherother packagespackages..

classesclasses inin thethe samesame packagepackage cancan alsoalso accessaccess

protectedprotected fields,fields, methodsmethods andand constructorsconstructorsasas well,well, eveneven ifif theythey areare notnot aa subclasssubclass ofof

thethe protectedprotected membersmembers classclass


d f ld f l difidifi JJ


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defaultdefault accessaccess modifiermodifier::-- JavaJava

provide

sprovide

s aade

fau

ltde

fau

lt spe

cifie

rspe

cifie

rw

hichw

hich isisusedused whenwhen nono acccessacccess modifiermodifier isis

presentpresent.. AnyAny class,class, field,field, methodmethod oror

constructorconstructor thatthat hashas nono declareddeclared

accessaccess modifiermodifier isis accessibleaccessible onlyonly byby

classessclassess inin thethe samesame packagepackage..

NoteNote::TheThe defaultdefault modifiermodifier isis notnot usedused forfor

fieldsfields andand methodsmethods withinwithin anan

interfaceinterface..

//Application of classes and objects


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class rectangle

{

int length, width; //Declaration of variables

void getData(int x, int y) //Definition of method

{

length=x;

width=y;

}

int rectArea()

{

int area = length * width;

return(area);

}

}

//Program Continue

Class RectArea


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{


{

int area1, area2;

Rectangle rect1=new Rectangle();

Rectangle rect2=new Rectangle();rect1.length=15;

rect2.width=10;

area1=rect1.length*rect1.width;

rect2=rect2.rectArea();System.out.println(Area1=+area1);

System.out.println(Area2=+area2);

}

}

//A simple Class Example.

l b


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class box

{

double width;

double height;

double depth;

void volume()

{

System.out.print( Volume is );

System.out.println(Width * height * depth );

}

}

//Program Continue

Class boxDemo3


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{


{

box mybox1=new box();

box mybox2=new box();

//assign values to mybox1s instance variables

mybox1.width=10;

mybox1.height=20;

mybox1.depth=15;

//assign different values to mybox2s instance variablesmybox2.width=3;

mybox2.height=6;

mybox2.depth=9;

//display volume of first box


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Mybox1.volume();

//display volume of second box

mybox2.volume();

}

}

Constructor


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JavaJava supportssupports aa specialspecial typetype ofof

method,method, calledcalled aa constructor,constructor, thatthatenablesenables anan objectobject toto initializeinitialize itselfitself

whenwhen itit isis createdcreated..

SomeSome rulesrules asas followsfollows..

ConstructorsConstructors havehave thethe samesame namename asas thethe

classclass itselfitself.. TheyThey dodo notnot specifyspecify aa returnreturn type,type, notnot eveneven voidvoid..

ThisThis isis becausebecause theythey returnreturn thethe instanceinstance ofof thethe

classclass itselfitself..

Constructor


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ThereThere areare ThreeThree typestypes constructorconstructor

defaultdefault constructorconstructor

ParameterizedParameterized constructorconstructor CopyCopy constructorconstructor

//Application of classes and objects with constructor

class rectangle


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class rectangle

{

int length, width; //Declaration of variables

rectangle(int x , int y) //Constructor method

{

length=x;

width=y;

}

int rectArea()

{

int area = length * width;

return(area);

}

}

//Program Continue


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Class RectArea

{public static void main (String args[ ])

{

Rectangle rect1=new Rectangle(15, 10); //Calling Constructor

int area1=rect1.rectArea();

System.out.println(Area1= +area1);

}

}

Methods Overloading


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InIn javajava itit isis possiblepossible toto createcreate methodsmethods

thatthat havehave samesame name,name, butbut differentdifferentparameterparameter listslists andand differentdifferent

definitionsdefinitions.. ThisThis isis calledcalled methodmethod

overloadingoverloading.. MethodMethod overloadingoverloading isisusedused whenwhen objectsobjects areare requiredrequired toto

performperform similarsimilar taskstasks butbut usingusing

differentdifferent inputinput parametersparameters..

//method overloading

class Room


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{

float length;

float breadth;

Room(float x, float y) //constructor 1

{

length=x; breadth=y;

}Room (float x) //constructor 2

{

length=breadth=x;

}

int area()

{

return(length*braadth);

}

Here, we are overloading the constructor


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method Room(). An object representing a

rectangular room will be created asRoom room1 = new room (25.0, 15.0);

//using constructor1

On the other hand, if the room is square,

then we may create the corresponding

object as.

Room room2 = new room (20.0);

//using constructor1

Static MembersStatic Members


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LetLet usus assumeassume thatthat wewe wantwant toto definedefine aa

membermember thatthat isis commoncommon toto allall thethe objectsobjectsandand accessedaccessed withoutwithout usingusing aa particularparticular

objectobject.. ThatThat is,is, thethe membermember belongsbelongs toto thethe

classclass asas aa wholewhole ratherrather thanthan thethe objectsobjectscreatedcreated fromfrom thethe classclass.. SuchSuch membermember cancan bebe

defineddefined asas followsfollows..

staticstatic intint countcount;;

staticstatic intint max(intmax(int x,x, intint y)y);;

//Defining and using static memebers

class Mathoperation

{


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{

static float mul(float x, float y)

{

return x*y;

}

static float divide(float x, float y)

{

return x/y;

}}

class Mathapplication

{


{

float a=Mathoperation.mul(4.0,5.0);float b=Mathoperation.divide(a,2.0);

System.out.println(b= +b);

}

}

//Nesting of methods

class Nesting

{


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{

int m, n;

Nesting (int x, int y) //constructor method

{

m = x;

n = y;

}

int largest()

{if (m>=n)

return(m);

else

return(n);

}

void display(){

int large=largest(); //calling a method

System.out.println(Largest value =+large);

}

}

//Program is continue

l N ti T t


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class NestingTest

{


{

Nesting nest= new Nesting (50, 40);

nest.display();

}

}

Inheritance: Extending A ClassInheritance: Extending A Class


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ReusabilityReusability isis yetyet anotheranother aspectaspect ofof OOPOOP

paradigmparadigm.. JavaJava ClassesClasses cancan bebe reusedreused ininseveralseveral waysways.. ThisThis isis basicallybasically donedone byby

creatingcreating newnew classes,classes, reusingreusing thethe propertiesproperties

ofof existingexisting onesones.. TheThe mechanismmechanism ofof derivingderivingaa newnew classclass fromfrom anan oldold oneone isis calledcalled

InheritanceInheritance.. TheThe oldold classclass knownknown asas thethe basebase

classclass oror supersuper classclass oror parentparent classclass andand thethenewnew oneone isis calledcalled thethe subclasssubclass oror derivedderived

classclass oror childchild classclass..

InheritanceInheritance


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TheThe inheritanceinheritance allowsallows subclassessubclasses toto inheritinherit

allall thethe variablesvariables andand methodsmethods ofof theirtheirparentparent classesclasses inheritanceinheritance maymay taketake

differentdifferent formsforms..

SingleSingle InheritanceInheritance (Only(Only oneone supersuper class)class)

MultipleMultiple InheritanceInheritance (several(several supersuper classes)classes)

HierarchicalHierarchical InheritanceInheritance (One(One supersuper class,class, manymany subclasses)subclasses)

MultilevelMultilevel InheritanceInheritance (Derived(Derived fromfrom derivedderived class)class)

InheritanceInheritance


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Defining a SubclassDefining a Subclass

AA subclasssubclass isis defineddefined asas followsfollows::

classclass subclassnamesubclassname extendsextends superclassnamesuperclassname

{{

variablesvariables declarationdeclaration;;

methodsmethods declarationdeclaration;;

}}

Note: Java does not directly implement multiple

inheritance. However, this concept is implemented using

a secondary inheritance path in the form of interfaces.

InheritanceInheritanceA


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A

B

Single InheritanceSingle Inheritance

B C D

HierarchicalHierarchical InheritanceInheritance

A

B

C

MultilevelMultilevel inheritanceinheritance

B

C

A

Multiple InheritanceMultiple Inheritance

//Application of single Inheritance

class Room


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class Room

{

int length;int breadth;

Room(int x, int y) //constructor

{

length=x; breadth=y;

}

int area()

{

return(length*braadth);

}

}

//Program continue

class BedRoom extends Room


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class BedRoom extends Room

{

int heigth;BedRoom(int x, int y, int z)

{

super(x, y)

height =z;

}

int volume()

{

return(length*breath*height);

}

//Program Continue


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class InherTest{ public static void main(String args[])

{

BedRoom room1=new BedRoom(14, 12, 10);

int area1=room1.area(); //superclass method

int volume1=room1.volume(); //base class method

System.out.println(Area1 = +area1);

System.out.println(Volume =+volume);

}

}

Subclass ConstructorSubclass Constructor


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AA subclasssubclass constructorconstructor isis usedused toto constructorconstructor thethe instanceinstance

variablesvariables ofof bothboth thethe subclasssubclass andand thethe superclasssuperclass.. TheThekeywordkeyword supersuper isis usedused subjectsubject toto thethe followingfollowing conditioncondition..

SuperSuper maymay onlyonly bebe usedused withinwithin aa subclasssubclass constructorconstructor

methodmethod

TheThe callcall toto superclasssuperclass constructorconstructor mustmust appearappear asas thethe

firstfirst statementstatement withinwithin thethe subclasssubclass constructorconstructor

TheThe parametersparameters inin thethe supersuper callcall mustmust matchmatch thethe orderorder

andand typetype ofof thethe instanceinstance variablevariable declareddeclared inin thethe

superclasssuperclass..

//Illustration of method overriding

class Super


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p

{

int x;Super (int x)

{

this.x=x;

}

void display()

{

System.out.println(Super x= +x);

}

}

Class Sub extends Super

{


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{

int y;

sub (int x, int y){

super(x);

this.y=y;

}

void display() //method defined again

{

System.out.println(Super x= +x);

System.out.println(Sub y= +y);

}

Class OverrideTest


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{


{

Sub s1= new Sub(100, 200);

s1.display();

}

}

Final Variable and MethodFinal Variable and Method


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AllAll thethe methodmethod andand variablesvariables cancan bebe overriddenoverridden byby

defaultdefault inin subclassessubclasses.. IfIf wewe wishwish toto preventprevent thethesubclassessubclasses fromfrom overridingoverriding thethe membersmembers ofof thethe

superclass,superclass, wewe cancan declaredeclare themthem asas finalfinal usingusing thethe

keywordkeyword finalfinal asas aa modifiermodifier..

ExampleExample::--

finalfinal intint SIZE=SIZE=100100;;

finalfinal voidvoid showstatusshowstatus()()

{{bodybody ofof functionfunction;;

}}

Note:Note:--


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MakingMaking aa methodmethod finalfinal ensuresensures thatthat thethefunctionalityfunctionality defineddefined inin thisthis methodmethod

willwill nevernever bebe alteredaltered inin anyany wayway..

Similarly,Similarly, thethe valuevalue ofof finalfinal variablevariable cancannevernever bebe changedchanged.. FinalFinal variables,variables,

behavebehave likelike classclass variablesvariables andand theythey dodo

notnot taketake anyany spacespace onon individualindividualobjectsobjects ofof thethe classclass..

Final ClassesFinal Classes

SometimesSometimes wewe maymay likelike toto preventprevent aa classclass beingbeing furtherfurther


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SometimesSometimes wewe maymay likelike toto preventprevent aa classclass beingbeing furtherfurther

subclassessubclasses forfor securitysecurity reasonsreasons.. AA classclass thatthat cancan notnot bebe

subclassedsubclassed isis calledcalled aa finalfinal classclass.. ThisThis isis achievedachieved inin javajava

usingusing thethe keywordkeyword finalfinal asas followsfollows::

finalfinalclassclass AclassAclass

{{bodybody ofofclassclass;;

}}

AnyAny attemptattempt toto inheritinherit thesethese classesclasses willwill causecause anan errorerror andand thethecompilercompiler willwill notnot allowallow itit.. DeclaringDeclaring aa classclass finalfinal preventsprevents anyany

unwantedunwanted extensionsextensions toto thethe classclass.. ItIt alsoalso allowsallows thethe compilercompiler toto

performperform somesome optimisationsoptimisations whenwhen aa methodmethod of of finalfinal classclass isis

invokedinvoked..

Private protected AccessPrivate protected Access

A field can be declared with two keywordsA field can be declared with two keywords


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A field can be declared with two keywordsA field can be declared with two keywords

private and protected together like:private and protected together like:Example:Example:

private protected int codeNumber;private protected int codeNumber;

This is gives a visibility level in between the

protected access and private access. This

modifier makes the fields visible in all subclassesregardless of what package they are in.

remember, these field are not accessible by other

classes in the same package.

Rules ofThumb for access modifiersRules ofThumb for access modifiers

GivenGiven belowbelow areare somesome simplesimple rulesrules ofof applyingapplying


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GivenGiven belowbelow areare somesome simplesimple rulesrules ofof applyingapplying

appropriateappropriate accessaccess modifiersmodifiers..

11.. UseUse publicpublic ifif thethe fieldfield isis toto bebe visiblevisible everwhereeverwhere..

22.. UseUse protectedprotected ifif thethe fieldfield isis toto bebe visiblevisible everywhereeverywhere

inin thethe currentcurrent packagepackage andand alsoalso subclassessubclasses inin thethe

otherother packagespackages..33.. UseUse defaultdefault ifif thethe fieldfield isis toto bebe visiblevisible everywhereeverywhere

inin thethe currentcurrent packagepackage onlyonly..

44.. UseUse ofof privateprivate protectedprotected ifif thethe fieldfield isis toto bebe visiblevisible

onlyonly inin subclasses,subclasses, regardlessregardless ofof packagespackages..

55.. UseUse privateprivate ifif thethe fieldfield isis notnot toto bebe visiblevisible anywhereanywhere

exceptexcept inin itsits ownown classclass..

Using abstract ClassesUsing abstract Classes

AnyAny ClassClass thatthat containscontains oneone oror moremore abstractabstract methodsmethods


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AnyAny ClassClass thatthat containscontains oneone oror moremore abstractabstract methodsmethods

mustmust alsoalso bebe declareddeclared abstractabstract.. ToTo declaredeclare aa classclass

abstract,abstract, youyou simplysimply useuse thethe abstractabstract keywordkeyword inin frontfront ofofthethe classclass keywordkeyword atat thethe beginningbeginning ofof thethe classclass

declarationdeclaration.. ThereThere cancan bebe nono objectsobjects ofof anan abstractabstract classclass..

ThatThat is,is, anan abstractabstract classclass cannotcannot bebe directlydirectly instantiatedinstantiated

withwith thethe newnew operatoroperator.. SuchSuch objectsobjects wouldwould bebe useless,useless,

becausebecause anan abstractabstract classclass isis notnot fullyfully defineddefined..

Also,Also, youyou cannotcannot declaredeclare abstractabstract constructors,constructors, oror

abstractabstract staticstatic methodsmethods.. AnyAny subclasssubclass onon anan abstractabstract

classclass mustmust eithereither implementimplement allall ofof thethe abstractabstract methodsmethods

inin thethe superclass,superclass, oror bebe itselfitself declareddeclared abstractabstract..

//A simple demonstration of abstract.

abstract class A

{


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{

Abstract void callme();

//Concrete methods are still allowed in abstract classes

void callmetoo( )

{

System.out.println(Bs implementation of callme.);

}}

class AbstractDemo

{

public static void main (String args[])

B b =new B();

b.callme();

b.callmetoo():

}

}

//Using abstract methods and classes

abstract class Figure


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abstract class Figure

{

double dim1;

double dim2;

Figure (double a, double b)

{

dim1=a;

dim2=b;

}//area is now an abstract method

abstract double area();

}

//Program is continue.

class rectangle extends Figure


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class rectangle extends Figure

{

Rectangle (double a, double b)

{

super (a, b);

}

double area()

{

System.out.println(Inside Area for Rectangle.);return dim1*dim2;

}

}


class Triangle extends Figure


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g g

{

Triangle (double a, double b)

{

super (a, b);

}

//override area for right triangle

double area()

{System.out.println(Inside Area forTriangle.);

return dim1*dim2/2;

}


class AbstractAreas


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{

public static void main (String args []){

//Figure f=newFigure(10,10); //illegal now

Rectangle r =new Rectangle(9,5);

Triangle t= newTriangle(10,8);

Figure figref; //this is ok, no object is created

figref=r;

System.out.println(Area is +figref.area());

figref=t;

System.out.println(Area is +figref.area());

}

}

Defining InterfacesDefining Interfaces

AnAn interfaceinterface isis basicallybasically aa kindkind ofof classclass LikeLike


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AnAn interfaceinterface isis basicallybasically aa kindkind ofof classclass.. LikeLike

classes,classes, interfacesinterfaces containcontain methodsmethods andandvariablesvariables butbut withwith aa majormajor differencedifference.. TheThe

differencedifference isis thatthat interfacesinterfaces definedefine onlyonly

abstractabstract methodsmethods andand finalfinal fieldsfields.. ThisThismeansmeans thatthat interfacesinterfaces dodo notnot specifyspecify anyany

codecode toto implementimplement thesethese methodsmethods andand datadata

fieldsfields containcontain onlyonly constantsconstants.. Therefore,Therefore, ititisis thethe responsibilityresponsibility ofof thethe classclass thatthat

implementsimplements anan interfaceinterface toto definedefine thethe codecode

forfor implementionimplemention ofof thesethese methodsmethods..

Syntax for defining InterfaceSyntax for defining Interface


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interfaceinterface InterfaceNameInterfaceName

{{

variablesvariables declarationdeclaration;;

methodsmethods declarationdeclaration;;

}}

HereHere InterfaceInterface isis thethe keykey wordword andand

InterfaceNameInterfaceName isis anyany validvalid javajava variable(Justvariable(Just

likelike classclass names)names)..

defining Interfacedefining Interface


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NOTENOTE:: ThatThat allall variablesvariables areare

declareddeclared asas constantsconstants.. MethodsMethods

declarationdeclaration willwill containcontain onlyonly aa listlist ofof

methodsmethods withoutwithout anyany bodybodystatementsstatements..

ExampleExample::--returnreturn--typetype methodnamemethodname11 ((parameter_listparameter_list));;

HereHere isis anan exampleexample ofof anan interfaceinterface definitiondefinition thatthat

containscontains twotwo variablesvariables andand oneone methodmethod


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interfaceinterface itemitem

{{

staticstatic finalfinal intint codecode ==10011001;;

staticstatic finalfinal StringString name=Fanname=Fan;;voidvoid display()display();;

}}

Note: That the code for the method is not included in theinterface and the method declaration simply ends with a

semicolon. The class that implements this interface must

define the code for the method

Extending InterfacesExtending InterfacesLikeLike classesclasses interfacesinterfaces cancan alsoalso bebe extendedextended ThatThat


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LikeLike classes,classes, interfacesinterfaces cancan alsoalso bebe extendedextended.. ThatThat

is,is, anan interfaceinterface cancan bebe subsub interfacedinterfaced fromfrom otherotherinterfacesinterfaces.. TheThe newnew subsub interfaceinterface willwill inheritinherit allall

thethe membersmembers ofof thethe subsub interfaceinterface inin thethe mannermanner

similarsimilar toto subclassessubclasses.. ThisThis isis achievedachieved usingusing thethe

keywordkeyword extendsextends asas shownshown belowbelow::

ExampleExample

interfaceinterface namename22 extendsextends namename11

{{

bodybody ofof namename22

}}

Extending InterfacesExtending InterfacesExampleExample::


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ExampleExample::

interfaceinterface ItemConstantsItemConstants{{

intint codecode 10011001;;

StringString Name=FANName=FAN;;

}}

interfaceinterface ItemMethodsItemMethods

{{

voidvoid display()display();;

}}

Example ContinuedExample Continued


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pp

Interface item extendsInterface item extends ItemConstantsItemConstants,, ItemMethodsItemMethods

{{

..

....

..

}}

Implementing InterfaceImplementing InterfaceInterfacesInterfaces areare usedused aa superclassessuperclasses whosewhose


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InterfacesInterfaces areare usedused aa superclassessuperclasses whosewhose

propertiesproperties areare inheritedinherited byby classesclasses.. ItIt isis thereforethereforenecessarynecessary toto createcreate aa classclass thatthat inheritsinherits thethe givengiven

interfaceinterface.. ThisThis isis donedone asas followsfollows::

ExampleExample::

classclass classnameclassname implementsimplements interfacenameinterfacename

{{

bodybody ofof classnameclassname;;

}}

HereHere thethe classclass classnameclassname implementsimplements thethe interfaceinterface

interfancenameinterfancename..AA moremore generalgeneral formform ofof implementationimplementation

maymay looklook likelike thisthis::

//Implementing interfaces

interface Area // interface defined


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{

final static float pi =3.14F;float compute (float x, float y);

}

class Rectangle implements Area //Interface Implemented

{

public float compute (float x, float y)

{

return(x*y);

}

}

//Program continue..

class Circle implements Area

{


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{

public float compute (float x, float y){

return(pi*x*y);

}

}

class InterfaceTest

{


{

Rectangle rect=new Rectangle();

Circle cir =new Circle();

Area area; //Interface Object

//Program continue..

area rect; //interface Object

i l ( f l ( ))


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System.out.println(Area of Rectangle =+area.compute(10, 20));

// area refers to cir objectarea = cir;

System.out.println(Area of Rectangle =+area.compute(10, 0));

}

}

The output is as follows:The output is as follows:

Area of Rectangle =200;Area of Rectangle =200;

Area of Circle =314;Area of Circle =314;

//Implementing multiple interfaces

class student


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{

int rollnumber;

void getNumber(int n)

{

rollNumber=n;

}

void putNumber()

{System.out.println(Roll no: + rollnumber);

}

}

//program Continue

class Test extends Student

{


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{

float part1, part2;void getMarks (flaot m1, float m2)

{

part1=m1;

part2=m2;

}

void putMarks()

{ System.out.println(Marks Obtained );

System.out.println(Part 1= +part1);

System.out.println(Part 2= +part2);

}

}

//program Continue

interface Sports


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{

float sportwt = 6.0F;

void putwt();

}

class results extends Test implements Sports

{

float total;

public void putwt(){

System.out.println(Sports Wt = +sportwt);

}

//program Continue

void display()


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void display()

{

total=part1+part2+sportwt;

putNumber();

putMarks();

putwt();

System.out.println(Total score= +total);}

}

//program Continue

class Hybrid


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y


{

Results student1=new Results();student1.getnumber(1234);

student1.getMarks(27.5F,33.0F);

student1.display();}

}

//program Continue


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Output of the ProgramRollno: 1234Rollno: 1234

Marks ObtainedMarks Obtained

part1=27.5part1=27.5part2=33part2=33

Sports wt=6;Sports wt=6;

total Score=66.5total Score=66.5

Java APIPackagesJava APIPackagesJavaJava APIAPI providesprovides largelarge numbernumber ofof classesclasses


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pp gg

groupedgrouped intointo differentdifferent packagespackages accordingaccording totofunctionalityfunctionality.. MostMost ofof thethe timetime wewe useuse packagespackages

availableavailable withwith thethe javajava APIAPI..

Java System Packages and their ClassesJava System Packages and their Classes

Language support classes. These are classes that java compiler itself

uses and therefore they are automatically imported. They include


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Java.langJava.languses and therefore they are automatically imported. They include

classes for primitive types, strings, math functions, threads and

exception

java.utiljava.util

Language utility classes such as vectors, date etc.

Java.io

Input/output support classes. They provide facilities for the input and

output of data.

Java.awt

Set of classes for implementing graphical user interface. They include

classes for windows, buttons, lists. Menus and so on.

Java.net

Classes for networking. They include classes for communicating with

local computers as well as with internet servers.

Java.applet

Classes for creating and implementing applets.

//The listing below show a package named package1

containing a single class ClassA


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package package1;

Public class ClassA

{

public void displayA(){

System.out.println(Class A);

}

}


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StaticImportStaticImport

StaticStatic importimport isis anotheranother languagelanguage


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StaticStatic importimport isis anotheranother languagelanguage

featurefeature.. ThisThis featurefeature eliminateseliminates thetheneedneed ofof qualifyingqualifying aa staticstatic membermember

withwith thethe classclass namename.. thethe staticstatic importimport

declarationdeclaration isis similarsimilar toto thatthat ofof importimport..

WeWe cancan useuse thethe importimport statementstatement toto

importimport classesclasses fromfrom packagespackages andand useusethemthem withoutwithout qualifyingqualifying thethe packagepackage..

//Use of static import

Import static java.lang.Math.*;

public class mathop


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public class mathop

{public static void circle (double r)

{

double area=PI*r*r;

System.out.println(The Area of circle is :+area);}


{

mathop obj =new mathop();

obj.circle(2,3);

}

}

Multithreaded ProgrammingMultithreaded ProgrammingMultithreadingMultithreading isis aa conceptualconceptual programmingprogramming


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paradigmparadigm wherewhere aa program(process)program(process) isis divideddivided

intointo twotwo oror moremore subprogaramssubprogarams (processes),(processes),

whichwhich cancan bebe implementedimplemented atat thethe samesame timetime inin

parallel,parallel, forfor example,example, oneone subprogramsubprogram cancan displaydisplay

anan animationanimation onon thethe screenscreen whilewhile anotheranother maymaybuildbuild thethe nextnext animationanimation toto bebe displayeddisplayed.. ThisThis isis

somethingsomething similarsimilar toto dividingdividing aa tasktask intointo subtaskssubtasks

andand assigningassigning themthem toto differentdifferent peoplepeople forforexecutionexecution independentlyindependently andand simultaneouslysimultaneously..

ThreadThreadAA th dth d ii i ili il tt th tth t


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AA threadthread isis similarsimilar toto aa programprogram thatthat

hashas singlesingle flowflow ofof controlcontrol .. ItIt hashas

beginning,beginning, aa body,body, andand anan end,end, andand

executesexecutes commandscommands sequentiallysequentially.. InInfact,fact, allall mainmain programsprograms inin ourour

earlierearlier examplesexamples cancan bebe calledcalled

singlesingle--threadedthreaded programsprograms..

Creating ThreadCreating Thread

CreatingCreating threadsthreads inin javajava isis simplesimple


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CreatingCreating threadsthreads inin javajava isis simplesimple..

ThreadsThreads areare implementedimplemented inin thethe formformofof objectsobjects thatthat containcontain aa methodmethod calledcalled

run()run().. TheThe run()run() methodmethod isis thethe heartheart

andand soulsoul ofof anyany threadthread.. ItIt makesmakes upup thethe

entireentire bodybody ofof threadthread andand isis thethe onlyonly

methodmethod inin whichwhich thethe threadsthreads behaviorbehaviorcancan bebe implementedimplemented.. AA typicaltypical run()run()

wouldwould appearappear asas followfollow..

public void run()

{


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.....

(Statements for implementing thread)

}

The run() method should be invoked by an object of the concerned

thread. This can achieved by creating the thread and initiating itwith the help of another thread method called start().

1. By Creating Thread classBy Creating Thread class

Define a class that extends thread class and override its run()

method with the code required by the thread.2. By Converting class to threadBy Converting class to thread

interface has only one method, run(), that is to be defined in

the method with the code to be executed by the thread.

Extending the Thread ClassExtending the Thread Classwewe cancan makemake ourour class,class, runnablerunnable asas threadthread byby


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extendingextending thethe classclass javajava..langlang..ThreadThread.. ThisThis givesgives usus

accessaccess toto allall thethe threadthread methodsmethods directlydirectly.. ItIt

includesincludes thethe followingfollowing stepssteps..

11.. DeclareDeclare thethe classclass asas extendingextending thethe ThreadThread

classclass..

22.. ImplementImplement thethe run()run() methodmethod thatthat isis responsibleresponsible forfor

executingexecuting thethe sequencesequence ofof codecode thatthat thethe threadthread willwill

executeexecute..33.. CreateCreate aa threadthread objectobject andand callcall thethe start()start() methodmethod toto

initiateinitiate thethe threadthread executionexecution..

//Creating threads using the thread class

Class A extends Thread


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Class A extends Thread

{public void run()

{

for( int i=1; i


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Class B extends Thread

{public void run()

{

for( int j=1; j


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Class C extends Thread

{public void run()

{

for( int k=1; k


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Class ThreadTest

{

public static void

java evolution

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