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JAVAFORBEGINNERS

1.IntroductiontoJava

2.Featuresofjava

3.DataTypes,VariablesandArrays

4.Operators

5.Controlstatements

6.Classesandmethods

7.Inheritance

8.PackagesandInterface

9.ExceptionHandling

10.EventHandling

11.TheAppletClass

12.MoreeBooksandApps

Disclaimer

ThiseBookcontentsisforinformationalandstudypurposesonly.TheKnowledgeflow

makesnoclaims,promises,orguaranteesabouttheaccuracy,completeness,oradequacy

ofthecontentsofthiseBookandnolegalliabilityorotherresponsibilityisacceptedby

Knowledgeflowforanyerrors,omissions,orstatementsonthiseBook.

IntroductiontoJava

JavawasdesignedandconceivedbyJamesGosling,PatrickNaughton,Chris

Warth,EdFrankandMikeSherdan,whichwasdoneatSunMicrosystemsinyear

1991.

Ittookalmost18monthsforjavatocomeintoexistenceasaworkingversion.

Initiallyjavawasknownas“Oak”,whichwasthenrenamedas“Java”inyear1995.

SincejavahadmuchhadmuchofitscharacterdesignedfromCandC++.

Thischaracterinheritedbythetwowellknownandsimpleprogrammingmakes

javamoreappealingtocomputeranditgiantswhichwouldleadtoalargescale

success.

Butjavaismisunderstoodasthesophisticatedinternetversionrepresentationof

C++.

IthassignificantdifferencepracticallyandphilosophicallywhencomparedtoC++.

IfyouhavegoodknowledgeinC++thenyouwillfindjavaasyourcupofteaand

youwillateaseusingandunderstandingjava.

LogoofJava

Therefore,therearetwomainreasonsfortheevolutionofthecomputerlanguages.

JavahadenhancedandrefinedtheobjectorientedscenarioofC++.Thisgavemore

featurestotheuserswhichareasfollows.

Multithreading.

Librarywhichwouldprovideeasyinternetaccess.

Oneofthejava’smagicwasthebytecode.Bytecodeissetofinstructionwhichis

highlyoptimizedanddesignedtobeexecutedbyJVM(JavaVirtualMachine).Itis

aninterpreterforbytecode.Thisleadtothedesignoftrulyportableprograms.

Javaredesignedtheinternetwithnewfeatureandnetworkedprogramwhichareas

follows.

Applets-Itisakindofjavaprogramthatistobetransmittedoverandexecuted

automaticallybyjavacompatiblewebbrowsers.

Security-Itprovidedthesecurityofdownloadingvariousappletsandprograms

frominternetwithoutcontaininganyvirusorTrojanhorses.

Portability-Sincethereislargeanddifferentkindofoperatingsystemsthereforeit

providesthefreedomofrunninginanyoperatingsystemsoitsprogramcanbeused

indifferentOSwithoutanyissuesofcompatibility.

Theevolutionsinjavaareasfollows.

Java1.0

Java1.1

Java1.2

J2SE

J2SE1.2

J2SE1.3

J2SE1.4

J2SE5

J2SE5madevariouschangestoJava

Thenewfeaturethatwasaddedisasfollow.

Generics

Annotations

Autoboxingandauto-unboxing

Enumerations

Enhanced,for-eachstyleforloop

Variable-lengtharguments

Staticimport

FormattedI/O

Concurrencyutilities

InJ2SE5,andthedeveloperskitwascalledJDK5.1.5usedasinternalversionnumber

andthisisreferredasdeveloperversionnumber.

Javabecamethecenterofinnovationincomputertechnologicalworld.Theexistenceof

JVMandbytecodechangedthescenarioofsecurityandportabilityintheprogramming

world.ThewaythenewideasareputintothelanguagehasbeenredefinedbytheJCPi.e.

javacommunityprocess.

FeaturesofJava

Object-orientedprogramming

Thisisthecorefeatureofjava.

Thisistomanagetheincreaseinthecomplexity.

Itprovidesaverysophisticatedandwelldefinedinterfaceforthedata.

Itisalsoknownasdatacontrollingaccesscode.

Anotherimportantfeatureofjavabeingobjectorientedisabstraction.

Complexitycanbemanagedusingabstraction.

ThethreeOOPprinciples

Encapsulation-Itsagendaistomanipulatethedataandkeepthedataisolatedand

safefromtheexternalinterferenceandmisuse.Theencapsulationisdonebytheuse

oftheprotectivewrapper.Thispreventstheexternalsourcesfromaccessingthedata

orthecode.

EncapsulationinJava

Inheritance-Inthistheobjectwouldacquirethepropertyofotherobjectpresent.It

justfollowstheconceptofthehierarchicalclassification.Thisconsistsofclasses,

subclasses.Inheritancealsoislinkedorinteractswithencapsulationaswell.

Inheritance

Polymorphism-Itismeansmanywaystocarryoutthemethodbutfromoneinput.

Polymorphism

Bytecode

Thisishighlyoptimizedbysetofinstructionsdesignedwhichisdesignedtobeexecuted

byJavavirtualmachinethatisJVM.

JVM

Itwasdesignedasaninterpreterforthebytecode.

Anotherfeatureofjavaprogramisthatitissimple.

Thisenablestheprofessionalstolearn.

Workinaveryeffectivemannerbutitisalsoveryeasytounderstand.

Robust

Theabilitythatincludescreatingarobustprogramthatcanbeamultiplatformprogram

aregivenaveryhighpriorityindesignofJava.

Multithreading

Therealworldrequirementsaremetbyjavawhichhelpstoachievetherequirementof

creatinginteractiveandnetworkedprograms.

Highperformance

Theadvantageofbeingamultiplatformfunctioningprogramhelpstofindthecross

platformsolution.

Itprovidesbenefitsofbeinganplatformindependentcodewiththehelpofjavarun

timesystem.

Distributed

Thisisbecauseitisbeendesignedfortheinternetwhichhasadistributed

environmentbecauseofthehandlingofTCP/IPprotocols.

Thisallowstheprogramtofindoutmethodsacrossanetwork.

URLisusedinthistoaccessafileoninternet.

ThispropertysupportsRMI(RemoteMethodInvocation).

Dynamic

Thisistheactionthatistakenduringtherun-timesuchastoresolve,verifyandadd

objects.

Itprovidesusthefunctionwhichwillallowustolinkcodedynamicallythatwillbe

safe.

Simpleprogram

/*Callthisfile“Example.java”*/

ClassExample{

Publicstaticvoidmain(stringargs[]){

System.out.println(“thisisasimplejavaprogram.”);

}

}

Commandlineargumenttopasstheclassnameis

C:\>javaExample

Simpleoutputoftheaboveprogram

thisisasimplejavaprogram.

Callingofthefileinjavacmd

Callingofthefile:“Example.java”.

DataTypes

Integers

Itincludeswholevaluedsignednumberswhichareasfollow.

Byte-Whosewidthis8anditrangesfrom-128to127.Itisthesmallestintegertype.Itis

usefulwhenuserisdealingwithstreamorflowingdatafromanetworkorafile.

Declarationoftwobytevariablescalledxandyisasfollow

Bytex,y;

Short-Thewidthofthistypeofintegeris16anditrangesfrom-32,768to32,767.Itis

theleastcommonlyuseddatatypeinjava.

Declaration

Shorta;

Shortb;

Int-Thewidthofthistypeofintegeris32anditrangesfrom-2,147,483,648to

2,147,483,647.Itismoreefficientascomparedtobyteandshort.Itiscommonlyusedto

controlloopsandindexedarrays.

Declaration

Inta;

Long-Thewidthofthistypeofintegeris64anditrangesfrom

-9,223,372,036,854,775,808to9,223,372,036,854,775,807.Thisisusedforthosevalues

whicharelargeenoughthattheintegercannothandlethem.

Declaration

Intlightspeed;

Longdays;

Longsecond;

Seconds=days*24*60*60;

Floatingpointtype

Thisisforrealnumbersusedforcalculationsuchassquareroots,sineandcosine.These

areoftwotypes.

Float-Widthinbitsis32andrangeisfrom1.4e-045to3.4e+038.Floatisusedasa

variabletypeforthefractionalcomponent,butspecifiessingleprecision.Itcanbeusedin

representingdollarsandcents.

Declaration

Floathightemp;

Double-Widthinbitsis64andrangeisfrom4.9e-324to1.8e+308.itisusedandis

optimizedinsuchawaythatIcanbeusedforhighspeedmathematiccalculation.Ithas

doubleprecisionwhichisfasterthanthesingleprecision.Functionsuchassin()andsqrt()

etc,returndoublevalues.

Declaration

Doublepi,r,a;

r=10.4;

pi=3.14;

a=pi*r*r;

Characters

Thedatatypeusedstoreordeclarecharacterinjavaischar.

Itis16-bittypeinjava.Rangeofacharis0to65,536.

Therearenocharswhicharenegativeinnature.

Programdemonstrationforchar

ClasscharExample

{

Publicstaticvoidmain(Stringargs[]){

Chara,b;

a=88;

b=’y’;

system.out.print(“aandb:“);

system.out.println(a+““+b);

}

}

Booleans

Itisaprimitivetypeforlogicalvalues.

Thistendshaveonlyoneoftwopossiblevalues,trueorfalse.

Itisgovernedbyiforforcontrolstatements.

Variables

Itisbasicunitofstorageandvariableshavescope,visibilityandlifetime.

Declarationofvariables

Intx,y,z;

Or

Intx=1,y=2,z=5;

Typeconversionandcasting

Ifthereisanycompatibilityexistingbetweentwotypesthenjavawouldautomatically

performstheconversion.

Javaautomaticconversion

Itwillbeperformedwhentwoconditionsaremet.

Whenthetwotypesarecompatible;

Destinationtypeislargerthanthesourcetype.

Afterthetwoconditionsarebeensatisfiedawideningconversiontakesplace.

Castingcompatibletypes

Itisasimpleandexplicittypeofconversion.

Whenafloatingtypeofconversionisattachedtoanintegertypethistypeof

conversioniscalledtruncation.

Itisakindofconversionsometimecallednarrowingconversion.

Arrays

Itisagroupofsimilarvariablesthatwouldbereferredbyacommonname.

Theelementavailableinthearrayisaccessedthroughindex.

Thiscanbecreatedandmayhaveoneormoredimension.

Typesofarrays

Therearetwomaintypesofarraysare.

1. One-dimensionalarrays

2. Multi-dimensionalarrays

One-dimensionalArrays

It’salistofsimilartypesofdata.Beforeyoucreatearrayyouneedtocreateavariableof

anytype.

Syntax

Typevariable-name[];

Intyear_month[];

Multi-dimensionalArrays

Itisarraysofarraysneedtospecifyeachdimensionalarrayvariables,additionalindex

usingothersquarebracketsrepresentedas.

InttwoD[][]=newint[6][7];

Operators

Therearefourmaintypesofoperator.

Arithmeticoperators

TheBitwiseoperators

Relationaloperators

Booleanlogicaloperators

Arithmeticoperators

Addition-Thisoperatorisusedtoaddthevalues.Itisrepresentedby“+“.For

example

A=a+4.

Subtraction-Thisoperatorisusedtosubtractthevalues.Itisrepresentedby“-“.

Forexample

A=a-4.

Multiplication-Thisoperatorisusedtomultiplythevalues.Itisrepresentedby“*“.

Forexample

A=a*4.

Division-Thisoperatorisusedtodividethevalues.Itisrepresentedby“/“.For

example

A=a/4.

Modulus-Thisoperatorisusedtofindtheremainderofthevalueswhendivided.It

isrepresentedby“%“.Forexample

A=2%4.WhereA=0.

Increment-Thisoperatorisusedtoincreasesitsoperandbyone.Itisrepresentedby

“++“.Forexample

a=a++whichisequaltoa=a+1.

Decrement:Thisoperatorisusedtodecreasesitsoperandsbyone.Itisrepresented

by“—“.Forexample

a=a—whichisequaltoa=a-1.

Bitwiseoperators

UnaryNOT-Thisinvertsallofthebitsofoperandcontainedanditisrepresentedby“~“.

Forexample

~00101010=11010101

And-Itproduces1bitifbothoperandsarealso1anditisrepresentedby“&“.

Forexample

00101010

&00001111

000101010

OR-Ifeitheroftheoperandisoneitproduces1andItisrepresentedby“|“.

Forexample

00101010

|00001111

00101111

XOR-Ifeitherofthebitoperandis1,thenresultisalsooneotherwiseits0anditis

representedby“^”.

Forexample

00101010

^00001111

00100101

Leftshift-Itshiftsormovesallofthebitsintheparticulargivenvaluetotheleftside

numberoftimesthatisbeendeclaredanditisrepresentedby” ≪ ”.

Rightshift-Itshiftsormovesallofthebitsintheparticulargivenvaluetotherightside

numberoftimesthatisbeendeclaredanditisrepresentedby” ≫ ”.

Relationaloperators

Equalto-Thisrelationoperatorshowsthatthevaluesareequaltoeachotheranditis

representedby“==”.

Notequalto-Thisrelationoperatorshowsthatthevaluesarenotequaltoeachotherand

itisrepresentedby“!=”.

Greaterthan-Thisrelationoperatorshowsthatonevalueisgreaterwhencomparedto

otheranditisrepresentedby“>”.

Lessthan-Thisrelationoperatorshowsthatonevalueislesswhencomparedtootherand

itisrepresentedby“<”.

Greaterthanorequalto-Thisrelationoperatorshowsthatonevalueisgreaterorequal

butnotlesswhencomparedtootheranditisrepresentedby“>=”.

Lessthanorequalto-Thisrelationoperatorshowsthatonevalueissmallerorequalbut

notgreaterwhencomparedtootheranditisrepresentedby“<=”.

Booleanlogicaloperators

LogicalAND-Itisrepresentedby“&”.

Forexample

A&B=Ifaisfalseandbistrueitresultsasfalse,butisbotharetrueitresultsas

true.Similarlywhenbotharefalseitresultsasfalse.

LogicalOR-Itissigned|.

Forexample

A|B=Ifaisfalseandbistrueitresultsastrue,butisbotharetrueitresultsas

true.Similarlywhenbotharefalseitresultsasfalse.

LogicalXOR-Itisshownusing“^”.

Forexample

A^B=Ifaisfalseandbistrueitresultsastrue,butisbotharetrueitresultsas

false.Similarlywhenbotharefalseitresultsasfalse.

LogicalUnaryNot-Itisdepictedas“!”.

Forexample

!A=Ifaisfalseitresultsastrue,butifaistrueitresultsasfalse.

Assignmentoperators

Theassignmentisthesingleequalsignthatisrepresentedby“=”.

Thegeneralrepresentation

var=expression;

Inthisthevariable,whichisrepresentedas var shouldbecompatiblewiththetypeof

expression.

Inta,b,c;

a=b=c=100;

The?Operator

Thisisusedforreplacementofifthenelsestatementsanditisrepresentedas“?”.

Forexample

expressiona?expressionb:expressionc

Thisaboveexamplestatesthatiftheexpressionaistruethenexpressionbisevaluated

otherwiseexpressioncisevaluated.

ControlStatements

Therethreetypesofstatementsinjava.

1. Selectionstatements

2. Iterationstatements

3. Jumpstatements

Selectionstatements

Itistomanagetheflowofprogramsthatistobeexecutedbasedonthedynamic

conditionswhichcanbeonlyrealizedduringtheruntime.

Itprovidesflexibility.

Ifstatement-Itprovidesdifferentpathsforexecutionofprogram.

Syntax

If(conditionprovided)statementa;

Else

Statementb;

Thismeansiftheconditionistrue,thenstatementaisexecutedbutiffalsethenstatement

bisexecuted.

Forexample

inta,b;

If(x<y)a=0;

Else

b=0;

Nowthereisonetypeofprocedureusingifstatementi.e.nestedifstatementanditisvery

commonmethodinprogrammingworld.

Forexample

If(a==10){

If(b<15)i=j;

If(c>50)p=q;

Else

i=p;

}

Else

i=q;

Now,thesecondifstatementintheparenthesisisassociatedwithelse.Anothertypeof

procedureisofusingifstatementistheif-else-ifladderstatement.

Forexample

If(condition)

Statement;

Elseif(condition)

Statement;

Elseif(condition)

Statement;

.

.

.

.

.

Else

Statement;

Switchstatements

Itisamultibranchedstatement.

Syntax

Switch(expression)

{

Casevalue1:

Statement

Break;

Casevalue2:

Statement

Break;

.

.

.

Casevalen:

Statement

Break;

Default:

Statement;

}

Thefunctioningoftheswitchstatementiscomparesthegivenvaluewithallthecasesand

whenthematchfoundtheprogramsequenceisexecuted.

Forexample

Classsampswitch{

Publicstaticvoidmain(stringargs[])

{

Switch(i)

{

Case0:

System.out.println(“iiszero.”);

Break;

Case1:

System.out.println(“iisone.”)

Break;

Default:

System.out.println(“iisgreaterthan4.”)

}

Output

iiszero.

iisone.

iisgreaterthan4.

iisgreaterthan4.

Exampleofnestedswitchloopprogram

Switch(countfigures)

{

Case1:

Switch(targetvalue)

{//nestedswitch//

Case0:

System.out.println(“targetiszero”;

Break;

Case1:

System.out.println(“targetisone”;

Break;

}

Break;

Case2://…

Importantfeaturesofswitchstatementare.

Switchstatementcanonlycheckforequalityunlikeif.

Therecannotbetwocasesconstantinthesameswitchwithidenticalvalues.

Itismoreeffectivethanusingthesetofnestedifstatement.

Iterationstatements

Thesestatementsareusedtocreateloop.Therearethreetypesofiterationstatementused

injava.

Whilestatement

Itsfunctionistorepeatorblockstatementwhileitscontrollingexpressionistrue.

Syntax

While(condition){

//bodyofloop

}

Theloopisexecutedwhentheconditionistrue.Whenitisfalsethecontrolwillpassto

thenextlineofthecodefollowingtheloop.

Forexample

Classwhile{

Publicstaticvoidmain(stringargs[])

{

Intn=5;

While(n>0)

{

System.out.println(“tick“+n);

n—;

}

}

}

Output

Itwilltick5times

Tick5

Tick4

Tick3

Tick2

Tick1

Do-whilestatement

Thisloopexecutesitsbodyatleastoncebecauseitcontainsitsconditionexpressionatthe

bottomoftheloop.

Syntax

do

{

System.out.println(“tick”+n);

n—;

}

Whilen>0);

}

}

Forstatement

Itisaverypowerfulaswellasveryversatileconstruct.

Theconditionwhatisprovidedinforstatementuntilandunlesstheconditionisnot

beensatisfieditwon’texecute.

Iftheconditionisevaluatedandthevalueisfalsethenitisterminated.

Syntax

For(initialize;condition;iterate)

{

Body

}

Forexample

Classfortick

{

Publicstaticvoidmain(stringargs[])

{

Intn;

For(n=11;n>0;n—);

}

}

Jumpstatements

Javasupportsthreejumpstatementswhichareasfollows.

1. Break

2. Continue

3. Return

Break

Itisusedtoterminateastatementwhichisinsequenceinaswitchstatementanditcanbe

usedforexitingaloop.SometimeItcanbeusedinsteadofgoto.

Continue

Itprovidesanearlyiterationforaloop.

Forexample

Classcontinue

{

Publicstaticvoidmain(stringargs[])

{

For(inti=0;i<5;i++)

{

System.out.print(i+““);

If(i%2==0)continue;

System.out.print(““);

}

}

}

Return

ItisusedtoreturnfromamethodandItisatransferbackcallingofthemethod.

Forexample

Classreturn{

Publicstaticvoidmain(stringargs[])

{

Booleant=true;

System.out.println(“return”);

If(t)return;

System.out.println(“thiswon’twork”);

}

}

ClassesandMethods

Classesmightcontainonlycodeordatabutmayalsocontainboth.Aclassisdeclaredby

keywordclassanditcanbecomplexinnature.

Syntax

Classclassname

{

Typeinstance-variablea;

Typeinstance-variableb;

.

.

.

Typeinstance-variablen;

}

Typemethoda(parameter-list)

{

//bodyofmethod

}

Typemethodnamea(parameter-list)

//bodyofmethod

.

.

}

}

Classesarealsocalledtheboxwhichdefinesvariable-width,heightanddepth.

Example

Classbox

{

Doublewidth;

Doubleheight;

Doubledepth;

}

Classthatimplementsstackofdataandinteger.

Example

Classstack

{

Intstk[]=newint[10];

Stack()

Tos=-1

}

Voidpush(intitem){

If(tos==9)

System.out.println(‘it’sfull”);

Else

Stk[++tos]=item;

}

Intpop()

{if(tos<0){

System.out.println(“stackunderflow”);

Return0;

}else

Returnstk[tos—];

}

}

Overloadingmethod

Whentwoormoremethodsaredefinedinthesameplaceandthenamedefinedissame

buttheparametersaredifferent.Thismethodisanoverloadingmethod.Thisprovides

polymorphisminjava.

Example

Classoverload1

{

Voidtest(){

System.out.println(“noparameter”);

}

Voidtest(inta)

{

System.out.println(“a:“+a);

}

Voidtest(inta,intb)

{

System.out.println(“aandb:“+a+““+b);

}

Doubletest(doublea)

{

System.out.println(“doublea:“+a);

Returna*a;

}

}

Classoverload

{

Publicstaticvoidmain(stringargs[])

{

Overload1ob=newoverload();

Doubleresult;

ob.test();

ob.test(10);

ob.test(10,20);

Result=ob.test(123.25);

System.out.println(“result:”+result);

}

}

Output

A=10

AandB=1020

Doublea=123.25

Result=15190.5625

Inheritance

Inheritanceisasuperclassfromwhichalltheclassesareinheritedandwhichdoes

inheritingfromasuperclassiscalledthesubclass.

Basicprogramofinheritance

Classx

{

inti,j;

voidshowIj()

{

System.out.println(“iandj:”+i+““+j);

}

}

Classyextendsx

Inta;{

System.out.println(“a:“+a);

}

Voidsum()

{

System.out.println(“i+j+a:“+(i+j+a));

}

}

Classsimpinheritance

{

Publicstaticvoidmain(stringargs[])

{

qSuperob=newq();

psuperob=newp();

Subob.i=8;

Subob.j=7;

Subob.a=9;

System.out.println(“contents”);

Subob.showij();

Subob.showa();

System.out.println(“sumofi,janda”);

}

}

Output

Contents:Iandj:87

a:9

Sumofi,janda:i+j+a:24

Mainuseofinheritanceinjavaisforoverridingandcodereusability.

Overriding

Whensubclassesareidenticalofasuperclassthisscenarioiscalledmethod

overriding.

Itprovidesthecharacteristiccalledpolymorphisminjava.

Inheritanceshowingoverriding

Examplecode

Classx{

inta,b

X(intp,intq)

{

p=a;

q=b;

}

Voidshow()

{

System.out.println(“aandb:“+i+”“+j);

}

}

Classyextendsx{

Intr;

Y(inta,intb,intc)

{

Super(a,b);

r=c;

}

Voidshow(){

System.out.println(“r:“+r);

}

}

Classoverride{

Publicstaticvoidmain(stringargs[])

{

ysubob=newy(1,2,3);

Subob.Show();

}

}

Output

r=3

Typesofinheritance

Therearethreetypesofinheritance.

Singleinheritance

Multipleinheritance

Hierarchicalinheritance

Typesofinheritance

Injavamultipleandhybridwillonlysupportedwithuseofinterface.

Multipleandhybridinheritance

Packages

Packagescontainnameswereclassesarestored.

Syntax

Packagepkg;

Torepresentmultipackaging

Packagepkgx[.pkgy[.pkgz]];

Forexample

Packagejava.awt.imagea;

Findingofpackages

Therearethreewaystofindthepackages.Thejavaruntimesystemusestheworking

directory;ifthepackageiscontainedinthesubdirectorythenitwillbediscoveredoryou

cansetthelocationbysettingthelocationofclassasshown.

Packagempack

Itcanuseclasspathwithjavaaswellasjavactospecifythe

locationofclassasshown.

C:\

myprograms\java\mpack

Accessprotection

Fortheprotectionofpackagestherearethreespecifiersinexistenceinjava.

1. Private-cannotbeseenoraccessedfromoutsidetheclass.

2. Public-ithasfeaturetobeaccessedfromanywhere.

3. Protected-thiscanbeaccessedonlybyclasseswhicharesub-classes.

Packagesyntax

Importingapackage

Thestatementthatimportsthepackagecomeimmediatelyafterthepackagingstatement

anditsmainfunctionistoimportthepackagebysavingmoretimetoitslocation.

Syntax

Importpkga[.pkgb].(classnamed*);

Interface

Itissimilartoclasswhichcontainsconstants,methodsandsignatures.

Javasimplecalculatorinterface

Interfaceforjava

Declaration

Accessinterfacem

{

Returnmethod1(parameterlist);

Returnmethod2(parameterlist);

Typefinalvariablename1=value;

Typefinalvariablename2=value;

//…

Returntypemethodnamen(parameterlist);

Typefinalvarnamen=value;

}

Simpleinterfacecontainsonlyonefunctionormethodknownascallbackfunction.

Forexample

Interfacecallback

{

Voidcallback(intparm);

}

Implementinginterface

Tocreatinganyinterfaceimplementationofclassisincludedindefinitionofaclass.

Forexample

Classclientcallback

{

Publicvoidcallback(intx)

{

System.out.println(“callback”+x);

}

}

ExceptionalHandling

Itisadrawbackthataffectstheperformanceofjavaprogrambecauseitcanoccuratany

point.Itoccurrenceisatexecutionstate.

Reasons

Invaliddata

Fileabsent

LossofnetworkconnectionandtimeoutwhentheJVMisatrun.

Thecommonexceptionsare.

Checked-Theseexceptionscannotbeforecastedbytheprogrammeranditcannotbeeven

ignoredduring.

Runtime-Thisisadynamicexception,butitcanbeignoredunlikethecheckedone.

Errors-Thesearealsoignoredbecausenothingcanbedonetoovercomeitandthisisnot

underprogrammer’scontrol.

Exceptionhierarchy

Ithastwosubdivisions:Inputoutputexceptionclassesandruntimeexceptionclass.

Throw

TheseareexceptionswhicharethrownbyJVMduringruntime.

Syntax

throwThrowableinstance;

Throw

Whenthisstatementisusedthereisanimmediatestopintheexecutionofprogram.

Forexample

Classthrowdem

{

Staticvoiddemopro()

{

Try{

ThrownewNullPointerException(“dem“);

}catch(NullPointerExceptione)

{

System.out.println(“caughtinsidedemopro.“);

Throwe;

}

}

Publicstaticvoidmain(stringargs[]{

Try{

Demopro();

}

Catch(NullPointerExceptione){

System.out.println(recatch:“+e);

}

}

}

Finally

Itisacodethatisusedinexecutingbeforeorafterthetryandcatchblockisexecutedor

completed.

Syntax

Classfinallydem

{

Staticvoidprox()

{

Try

{

System.out.println(“inprocx”);

ThrownewruntimeException(“demo”);

}

Finally

{

System.out.println(“proxfinally”);

}

}

Eventhandling

Event

Itshowsthechangeinstateofasource.

Eventsources

Itisanobjectgeneratinganevent.

Syntax

PublicvoidaddTypeListener(TypeListnerl)

Forexample

Addkeylistner()-toregisterakeyboardevent.

Addmousemotionlistner()-toregisteramousemotionlistener.

ActionEventClass

Thishappenswhenbuttonispressed.Doubleclickingoftheitemoranyiteminthemenu

isselected.

Eventoccurrenceinjava

Keyeventclass

Thisgeneratedfromthekeyinputofthekeyboardandtherearethreetypesofkeyevents.

1. KEY_PRESSED

2. KEY_RELEASED

3. KEY_TYPED.

Mouseeventclass

Thereareeighttypesofmouseeventclasses.

1. MOUSE_DRAGGED

2. MOUSE_CLICKED

3. MOUSE_ENTERED

4. MOUSE_EXITED

5. MOUSE_MOVED

6. MOUSE_PRESSED

7. MOUSE_RELEASED

8. MOUSE_WHEELED

Actionlistenerinterface

Itisusedtodefinetheactionstheseareallperformedwhichareinvokedatthecallofan

event.Itisusedtoknowthereactionofthemethod.

TheAppletclass

Itcontainsseveralmethodswhichareusefulforjavaexecutionanddetailedcontrol.The

Appletinitializationandterminationareasfollow.

Forstarting

init()-Usedtoinitializemethoditisthefirstmethod.

start()-Afterinitializationmethodthismethodcomesanditsfunctionistorestartor

displayonscreen.

paint()-Inthistheoutputoftheappletisredrawneachtimeitiscalled.

Forstopping

stop()-Itistoleavethebrowserwhichisopenedandcontainsapplet.

destroy()-Itisfortheappletoncewhichhastoremovedfromthememory.

Appletgeneration

HTMLapplettag

<APPLET

[CODEBASE=codebaseurl]

CODE=appletfile

[ALT=alternatetext]

[NAME=appletinstancename]

WIDTH=pixelsHEIGHT=pixels

[ALIGN=alignment]

[VSPACE=pixels][HSPACE=pixels]

>

[PARANAME=attributenameVALUE=attributevalue>]

…

[HTMLdisplayedinabsenceofjava]

</APPLET>

HTMLApplettag

TheAudioclipinterface

play()-Tobegintheaudio.

stop()-Tostoptheaudio.

loop()-Toplaytheloopwithoutbreak.

TheAppletsubinterface

ItprovidesalinkthroughwhichanAppletandthebrowsercancommunicate.

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