java interview questions

6/16/2015 JavaInterviewQuestions

http://javatooj2ee.blogspot.in/2014/06/javainterviewquestions1.html 1/48

28thJune2014

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1.WhatisJVM?TheJavainterpreteralongwiththeruntimeenvironmentrequiredtoruntheJavaapplicationincalledasJavavirtualmachine(JVM)

2.WhatisthemostimportantfeatureofJava?Javaisaplatformindependentlanguage.

3.Whatdoyoumeanbyplatformindependence?Platformindependencemeansthatwecanwriteandcompilethejavacodeinoneplatform(egWindows)andcanexecutetheclassinanyothersupportedplatformeg(Linux,Solaris,etc).

4.WhatisthedifferencebetweenaJDKandaJVM?JDKisJavaDevelopmentKitwhichisfordevelopmentpurposeanditincludesexecutionenvironmentalso.ButJVMispurelyaruntimeenvironmentandhenceyouwillnotbeabletocompileyoursourcefilesusingaJVM.

5.Whatisthebaseclassofallclasses?java.lang.Object

6.WhataretheaccessmodifiersinJava?Thereare3accessmodifiers.Public,protectedandprivate,andthedefaultoneifnoidentifierisspecifiediscalledfriendly,butprogrammercannotspecifythefriendlyidentifierexplicitly.

7.Whatisarepackages?Apackageisacollectionofrelatedclassesandinterfacesprovidingaccessprotectionandnamespacemanagement.

JavaInterviewQuestions

JavainterviewQuestions



8.WhatismeantbyInheritanceandwhatareitsadvantages?Inheritanceistheprocessofinheritingallthefeaturesfromaclass.Theadvantagesofinheritancearereusabilityofcodeandaccessibilityofvariablesandmethodsofthesuperclassbysubclasses.

9.Whatisthedifferencebetweensuperclassandsubclass?Asuperclassisaclassthatisinheritedwhereassubclassisaclassthatdoestheinheriting.

10.Whatisanabstractclass?Anabstractclassisaclassdesignedwithimplementationgapsforsubclassestofillinandisdeliberatelyincomplete.

11.Whatarethestatesassociatedinthethread?Threadcontainsready,running,waitinganddeadstates.

12.Whatissynchronization?Synchronizationisthemechanismthatensuresthatonlyonethreadisaccessedtheresourcesatatime.

13.Whatisdeadlock?Whentwothreadsarewaitingeachotherandcantprecedetheprogramissaidtobedeadlock.

14.Whatisanapplet?Appletisadynamicandinteractiveprogramthatrunsinsideawebpagedisplayedbyajavacapablebrowser

15.Whatisthelifecycleofanapplet?init()methodCanbecalledwhenanappletisfirstloadedstart()methodCanbecalledeachtimeanappletisstarted.paint()methodCanbecalledwhentheappletisminimizedormaximized.stop()methodCanbeusedwhenthebrowsermovesofftheappletspage.destroy()methodCanbecalledwhenthebrowserisfinishedwiththeapplet.

16.Howdoyousetsecurityinapplets?usingsetSecurityManager()method

17.WhatisalayoutmanagerandwhataredifferenttypesoflayoutmanagersavailableinjavaAWT?Alayoutmanagerisanobjectthatisusedtoorganizecomponentsinacontainer.ThedifferentlayoutsareavailableareFlowLayout,BorderLayout,CardLayout,GridLayoutandGridBagLayout

18.WhatisJDBC?JDBCisasetofJavaAPIforexecutingSQLstatements.ThisAPIconsistsofasetofclassesandinterfacestoenableprogramstowritepureJavaDatabaseapplications.

19.Whataredriversavailable?a)JDBCODBCBridgedriverb)NativeAPIPartlyJavadriverc)JDBCNetPureJavadriverd)NativeProtocolPureJavadriver

20.Whatisstoredprocedure?StoredprocedureisagroupofSQLstatementsthatformsalogicalunitandperformsaparticulartask.StoredProceduresareusedtoencapsulateasetofoperationsorqueriestoexecuteondatabase.Storedprocedurescanbecompiledandexecutedwithdifferentparametersandresultsandmayhaveanycombinationofinput/outputparameters.

21.WhatistheJavaAPI?TheJavaAPIisalargecollectionofreadymadesoftwarecomponentsthatprovidemanyusefulcapabilities,suchasgraphicaluserinterface(GUI)widgets.



22.WhytherearenoglobalvariablesinJava?Globalvariablesaregloballyaccessible.Javadoesnotsupportgloballyaccessiblevariablesduetofollowingreasons:1)Theglobalvariablesbreaksthereferentialtransparency2)Globalvariablescreatescollisionsinnamespace.

23.WhatareEncapsulation,InheritanceandPolymorphism?Encapsulationisthemechanismthatbindstogethercodeanddataitmanipulatesandkeepsbothsafefromoutsideinterferenceandmisuse.Inheritanceistheprocessbywhichoneobjectacquiresthepropertiesofanotherobject.Polymorphismisthefeaturethatallowsoneinterfacetobeusedforgeneralclassactions.

24.WhatistheuseofbinandlibinJDK?Bincontainsalltoolssuchasjavac,appletviewer,awttool,etc.,whereaslibcontainsAPIandallpackages.

25.Whatismethodoverloadingandmethodoverriding?Methodoverloading:Whenamethodinaclasshavingthesamemethodnamewithdifferentargumentsissaidtobemethodoverloading.Methodoverriding:Whenamethodinaclasshavingthesamemethodnamewithsameargumentsissaidtobemethodoverriding.

26.Whatisthedifferencebetweenthis()andsuper()?this()canbeusedtoinvokeaconstructorofthesameclasswhereassuper()canbeusedtoinvokeasuperclassconstructor.

27.WhatisDomainNamingService(DNS)?Itisverydifficulttorememberasetofnumbers(IPaddress)toconnecttotheInternet.TheDomainNamingService(DNS)isusedtoovercomethisproblem.ItmapsoneparticularIPaddresstoastringofcharacters.Forexample,www.mascom.comimpliescomisthedomainnamereservedforUScommercialsites,moscomisthenameofthecompanyandwwwisthenameofthespecificcomputer,whichismascomsserver.

28.WhatisURL?URLstandsforUniformResourceLocatoranditpointstoresourcefilesontheInternet.URLhasfourcomponents:http://www[http://www/].address.com:80/index.html,wherehttpprotocolname,addressIPaddressorhostname,80portnumberandindex.htmlfilepath.

29.WhatisRMIandstepsinvolvedindevelopinganRMIobject?RemoteMethodInvocation(RMI)allowsjavaobjectthatexecutesononemachineandtoinvokethemethodofaJavaobjecttoexecuteonanothermachine.ThestepsinvolvedindevelopinganRMIobjectare:a)Definetheinterfacesb)Implementingtheseinterfacesc)Compiletheinterfacesandtheirimplementationswiththejavacompilerd)CompiletheserverimplementationwithRMIcompilere)RuntheRMIregistryf)Runtheapplication.

30.WhatisRMIarchitecture?RMIarchitectureconsistsoffourlayersandeachlayerperformsspecificfunctions:a)Applicationlayercontainstheactualobjectdefinition.b)Proxylayerconsistsofstubandskeleton.c)RemoteReferencelayergetsthestreamofbytesfromthetransportlayerandsendsittotheproxylayer.d)Transportationlayerresponsibleforhandlingtheactualmachinetomachinecommunication.

31.WhatisaJavaBean?AJavaBeanisasoftwarecomponentthathasbeendesignedtobereusableinavarietyofdifferentenvironments.32.Whatarecheckedexceptions?CheckedexceptionarethosewhichtheJavacompilerforcesyoutocatch.e.g.IOExceptionarecheckedExceptions.



33.Whatareruntimeexceptions?Runtimeexceptionsarethoseexceptionsthatarethrownatruntimebecauseofeitherwronginputdataorbecauseofwrongbusinesslogicetc.Thesearenotcheckedbythecompileratcompiletime.

34.Whatisthedifferencebetweenerrorandanexception?Anerrorisanirrecoverableconditionoccurringatruntime.SuchasOutOfMemoryerror.TheseJVMerrorsandyoucannotrepairthematruntime.Whileexceptionsareconditionsthatoccurbecauseofbadinputetc.e.g.FileNotFoundExceptionwillbethrownifthespecifiedfiledoesnotexist.OraNullPointerExceptionwilltakeplaceifyoutryusinganullreference.Inmostofthecasesitispossibletorecoverfromanexception(probablybygivinguserafeedbackforenteringpropervaluesetc.).

35.Whatisthepurposeoffinalization?Thepurposeoffinalizationistogiveanunreachableobjecttheopportunitytoperformanycleanupprocessingbeforetheobjectisgarbagecollected.Forexample,closingaopenedfile,closingaopeneddatabaseConnection.

36.Whatisthedifferencebetweenyieldingandsleeping?Whenataskinvokesitsyield()method,itreturnstothereadystate.Whenataskinvokesitssleep()method,itreturnstothewaitingstate.

37.Whatisthedifferencebetweenpreemptiveschedulingandtimeslicing?Underpreemptivescheduling,thehighestprioritytaskexecutesuntilitentersthewaitingordeadstatesorahigherprioritytaskcomesintoexistence.Undertimeslicing,ataskexecutesforapredefinedsliceoftimeandthenreentersthepoolofreadytasks.Theschedulerthendetermineswhichtaskshouldexecutenext,basedonpriorityandotherfactors.

38.Whatismutableobjectandimmutableobject?IfaobjectvalueischangeablethenwecancallitasMutableobject.(Ex.,StringBuffer,)Ifyouarenotallowedtochangethevalueofanobject,itisimmutableobject.(Ex.,String,Integer,Float,)39.WhatisthepurposeofVoidclass?TheVoidclassisanuninstantiableplaceholderclasstoholdareferencetotheClassobjectrepresentingtheprimitiveJavatypevoid.

40.WhatisJITanditsuse?Really,justaveryfastcompilerInthisincarnation,prettymuchaonepasscompilernoofflinecomputations.Soyoucantlookatthewholemethod,ranktheexpressionsaccordingtowhichonesarereusedthemost,andthengeneratecode.Intheoryterms,itsanonlineproblem.

41.Whatisnestedclass?Ifallthemethodsofainnerclassisstaticthenitisanestedclass.42.WhatisHashMapandMap?MapisInterfaceandHashmapisclassthatimplementsthat.43.Whataredifferenttypesofaccessmodifiers?public:Anythingdeclaredaspubliccanbeaccessedfromanywhere.private:Anythingdeclaredasprivatecantbeseenoutsideofitsclass.protected:Anythingdeclaredasprotectedcanbeaccessedbyclassesinthesamepackageandsubclassesintheotherpackages.defaultmodifier:Canbeaccessedonlytoclassesinthesamepackage.

44.WhatisthedifferencebetweenReader/WriterandInputStream/OutputStream?TheReader/WriterclassischaracterorientedandtheInputStream/OutputStreamclassisbyteoriented.

45.Whatisservlet?Servletsaremodulesthatextendrequest/responseorientedservers,suchasjavaenabledwebservers.Forexample,aservletmightberesponsiblefortakingdatainanHTMLorderentryformandapplyingthebusiness



logicusedtoupdateacompanysorderdatabase.

46.WhatisConstructor?Aconstructorisaspecialmethodwhosetaskistoinitializetheobjectofitsclass.Itisspecialbecauseitsnameisthesameastheclassname.Theydonothavereturntypes,notevenvoidandthereforetheycannotreturnvalues.Theycannotbeinherited,thoughaderivedclasscancallthebaseclassconstructor.Constructorisinvokedwheneveranobjectofitsassociatedclassiscreated.

47.WhatisanIterator?TheIteratorinterfaceisusedtostepthroughtheelementsofaCollection.IteratorsletyouprocesseachelementofaCollection.IteratorsareagenericwaytogothroughalltheelementsofaCollectionnomatterhowitisorganized.IteratorisanInterfaceimplementedadifferentwayforeveryCollection.

48.WhatistheListinterface?TheListinterfaceprovidessupportfororderedcollectionsofobjects.Listsmaycontainduplicateelements.

49.Whatismemoryleak?Amemoryleakiswhereanunreferencedobjectthatwillneverbeusedagainstillhangsaroundinmemoryanddoesntgetgarbagecollected.

50.Whatisthedifferencebetweentheprefixandpostfixformsofthe++operator?Theprefixformperformstheincrementoperationandreturnsthevalueoftheincrementoperation.Thepostfixformreturnsthecurrentvaluealloftheexpressionandthenperformstheincrementoperationonthatvalue.

51.Whatisthedifferencebetweenaconstructorandamethod?Aconstructorisamemberfunctionofaclassthatisusedtocreateobjectsofthatclass.Ithasthesamenameastheclassitself,hasnoreturntype,andisinvokedusingthenewoperator.Amethodisanordinarymemberfunctionofaclass.Ithasitsownname,areturntype(whichmaybevoid),andisinvokedusingthedotoperator.

52.WhatwillhappentotheExceptionobjectafterexceptionhandling?Exceptionobjectwillbegarbagecollected.

53.Differencebetweenstaticanddynamicclassloading.Staticclassloading:Theprocessofloadingaclassusingnewoperatoriscalledstaticclassloading.Dynamicclassloading:Theprocessofloadingaclassatruntimeiscalleddynamicclassloading.DynamicclassloadingcanbedonebyusingClass.forName(.).newInstance().

54.ExplaintheCommonuseofEJBTheEJBscanbeusedtoincorporatebusinesslogicinawebcentricapplication.TheEJBscanbeusedtointegratebusinessprocessesinBusinesstobusiness(B2B)ecommerceapplications.InEnterpriseApplicationIntegrationapplications,EJBscanbeusedtohouseprocessingandmappingbetweendifferentapplications.

55.WhatisJSP?JSPisatechnologythatreturnsdynamiccontenttotheWebclientusingHTML,XMLandJAVAelements.JSPpagelookslikeaHTMLpagebutisaservlet.ItcontainsPresentationlogicandbusinesslogicofawebapplication.

56.Whatisthepurposeofapachetomcat?ApacheserverisastandaloneserverthatisusedtotestservletsandcreateJSPpages.Itisfreeandopen



sourcethatisintegratedintheApachewebserver.Itisfast,reliableservertoconfiguretheapplicationsbutitishardtoinstall.Itisaservletcontainerthatincludestoolstoconfigureandmanagetheservertoruntheapplications.ItcanalsobeconfiguredbyeditingXMLconfigurationfiles.

57.Wherepragmaisused?Pragmaisusedinsidetheservletsintheheaderwithacertainvalue.Thevalueisofnocachethattellsthataservletsisactingasaproxyandithastoforwardrequest.PragmadirectivesallowthecompilertousemachineandoperatingsystemfeatureswhilekeepingtheoverallfunctionalitywiththeJavalanguage.Thesearedifferentfordifferentcompilers.

58.Brieflyexplaindaemonthread.Daemonthreadisalowprioritythreadwhichrunsinthebackgroundperformsgarbagecollectionoperationforthejavaruntimesystem.

59.Whatisanativemethod?AnativemethodisamethodthatisimplementedinalanguageotherthanJava.

60.Explaindifferentwayofusingthread?AJavathreadcouldbeimplementedbyusingRunnableinterfaceorbyextendingtheThreadclass.TheRunnableismoreadvantageous,whenyouaregoingformultipleinheritance.

61.WhatarethetwomajorcomponentsofJDBC?Oneimplementationinterfacefordatabasemanufacturers,theotherimplementationinterfaceforapplicationandappletwriters.

62.WhatkindofthreadistheGarbagecollectorthread?Itisadaemonthread.

63.Whatarethedifferentwaystohandleexceptions?Therearetwowaystohandleexceptions,1.Bywrappingthedesiredcodeinatryblockfollowedbyacatchblocktocatchtheexceptions.and2.Listthedesiredexceptionsinthethrowsclauseofthemethodandletthecallerofthemethodhandlethoseexceptions.

64.Howmanyobjectsarecreatedinthefollowingpieceofcode?MyClassc1,c2,c3c1=newMyClass()c3=newMyClass()Answer:Only2objectsarecreated,c1andc3.Thereferencec2isonlydeclaredandnotinitialized.

65.WhatisUNICODE?Unicodeisusedforinternalrepresentationofcharactersandstringsandituses16bitstorepresenteachother

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Top 371 Java FAQs Useful for Freshers and Experienced

Q1.WhatisthedifferencebetweenanAbstractclassandInterface?1. Abstract classes may have some executable methods and methods leftunimplemented.Interfacescontainnoimplementationcode.2. Anclasscan implementanynumberof interfaces,butsubclassatmostoneabstract



class.3. Anabstractclasscanhavenonabstractmethods.Allmethodsofaninterfaceareabstract.4.Anabstractclasscanhaveinstancevariables.Aninterfacecannot.5.Anabstractclasscandefineconstructor.Aninterfacecannot.6.Anabstractclasscanhaveanyvisibility:public,protected,privateornone(package).Aninterface'svisibilitymustbepublicornone(package).7. Anabstractclass inherits fromObjectand includesmethodssuchasclone()andequals().

Q2.Whatarecheckedanduncheckedexceptions?Javadefinestwokindsofexceptions:Checkedexceptions:ExceptionsthatinheritfromtheExceptionclassarecheckedexceptions.ClientcodehastohandlethecheckedexceptionsthrownbytheAPI,either inacatchclauseorbyforwardingitoutwardwiththethrowsclause.ExamplesSQLException,IOxception.Uncheckedexceptions:RuntimeExceptionalsoextendsfromException.However,alloftheexceptionsthatinheritfromRuntimeExceptiongetspecialtreatment.Thereisnorequirementfortheclientcodetodealwiththem,andhencetheyarecalleduncheckedexceptions.ExampleUncheckedexceptionsareNullPointerException,OutOfMemoryError,DivideByZeroExceptiontypically,programmingerrors.

Q3.Whatisauserdefinedexception?Userdefinedexceptionsmaybeimplementedbydefiningaclasstorespondtotheexceptionandembeddingathrowstatementinthetryblockwheretheexceptioncanoccurordeclaringthatthemethodthrowstheexception(toanothermethodwhereitishandled).ThedevelopercandefineanewexceptionbyderivingitfromtheExceptionclassasfollows:publicclassMyExceptionextendsException{/*classdefinitionofconstructors(butNOTtheexceptionhandlingcode)goesherepublicMyException(){super()}public MyException( String errorMessage ) { super(errorMessage)}

[https://www.blogger.com/null]

}Thethrowstatementisusedtosignaltheoccuranceoftheexceptionwithinatryblock.Often,exceptionsareinstantiatedinthesamestatementinwhichtheyarethrownusingthesyntax.thrownewMyException("Ithrewmyownexception.")Tohandletheexceptionwithinthemethodwhereitisthrown,acatchstatementthathandlesMyException,mustfollowthetryblock.Ifthedeveloperdoesnotwanttohandletheexceptioninthemethoditself,themethodmustpasstheexceptionusingthesyntax:publicmyMethodName()throwsMyException

Q4.WhatisthedifferencebetweenC++&Java?WellasBjarneStroustrupsays"..despitethesyntacticsimilarities,C++andJavaareverydifferentlanguages.Inmanyways,JavaseemsclosertoSmalltalkthantoC++..".HerearefewIdiscovered:JavaismultithreadedJavahasnopointersJavahasautomaticmemorymanagement(garbagecollection)



Javaisplatformindependent(Stroustrupmaydifferbysaying"Javaisaplatform"JavahasbuiltinsupportforcommentdocumentationJavahasnooperatoroverloadingJavadoesntprovidemultipleinheritanceTherearenodestructorsinJava

Q5.WhatarestatementsinJAVA?Statementsareequivalenttosentencesinnaturallanguages.Astatementformsacompleteunitofexecution.ThefollowingtypesofexpressionscanbemadeintoastatementbyterminatingtheexpressionwithasemicolonAssignmentexpressionsAnyuseof++orMethodcallsObjectcreationexpressionsThesekindsofstatementsarecalledexpressionstatements.Inadditiontothesekindsofexpressionstatements,therearetwootherkindsofstatements.Adeclarationstatementdeclaresavariable.Acontrolflowstatementregulatestheorderinwhichstatementsgetexecuted.Theforloopandtheifstatementarebothexamplesofcontrolflowstatements.

Q6.WhatisJARfile?JavaARchivefilesareabigglobofJavaclasses,images,audio,etc.,

compressedtomakeonesimple,smallerfiletoeaseAppletdownloading.Normallywhenabrowserencountersanapplet,itgoesanddownloadsallthefiles,images,audio,usedbytheAppletseparately.Thiscanleadtoslowerdownloads.

Q7.WhatisJNI?JNIisanacronymofJavaNativeInterface.UsingJNIwecancallfunctionswhicharewritteninotherlanguagesfromJava.Followingareitsadvantagesanddisadvantages.Advantages:Youwanttouseyourexistinglibrarywhichwaspreviouslywritteninotherlanguage.YouwanttocallWindowsAPIfunction.Forthesakeofexecutionspeed.YouwanttocallAPIfunctionofsomeserverproductwhichisincorc++fromjavaclient.Disadvantages:Youcantsaywriteoncerunanywhere.Difficulttodebugruntimeerrorinnativecode.Potentialsecurityrisk.YoucantcallitfromApplet.

Q8.Whatisserialization?Quitesimply,objectserializationprovidesaprogramtheabilitytoreadorwriteawholeobjecttoandfromarawbytestream.ItallowsJavaobjectsandprimitivestobeencodedintoabytestreamsuitableforstreamingtosometypeofnetworkortoafilesystem,ormoregenerally,toatransmissionmediumorstoragefacility.AseralizableobjectmustimplementtheSerilizableinterface.WeuseObjectOutputStreamtowritethisobjecttoastreamandObjectInputStreamtoreaditfromthestream.

Q9.Whytherearesomenullinterfaceinjava?Whatdoesitmean?GivemesomenullinterfacesinJAVA?Nullinterfacesactasmarkers..theyjusttellthecompilerthattheobjectsofthisclassneedtobetreateddifferently..somemarkerinterfacesare:Serializable,Remote,Cloneable.



Q10.Issynchronizedamodifier?Identifier?Whatisit??It'samodifier.Synchronizedmethodsaremethodsthatareusedtocontrolaccesstoanobject.Athreadonlyexecutesasynchronizedmethodafterithasacquiredthelockforthemethod'sobjectorclass.Synchronizedstatementsaresimilartosynchronizedmethods.Asynchronizedstatementcanonlybeexecutedafterathreadhasacquiredthelockfortheobjectorclassreferencedinthesynchronizedstatement.

Q11.Whatissingletonclass?whereisitused?Singletonisadesignpatternmeanttoprovideoneandonlyoneinstanceofanobject.Otherobjectscangetareferencetothisinstancethroughastaticmethod(classconstructoriskeptprivate).Whydoweneedone?Sometimesitisnecessary,andoftensufficient,tocreateasingleinstanceofagivenclass.Thishasadvantagesinmemorymanagement,andforJava,ingarbagecollection.Moreover,restrictingthenumberofinstancesmaybenecessaryordesirablefortechnologicalorbusinessreasonsforexample,wemayonlywantasingleinstanceofapoolofdatabaseconnections.

Q12.Whatisacompilationunit?Thesmallestunitofsourcecodethatcanbecompiled,i.e.a.javafile.

Q13.Isstringsawrapperclass?Stringisaclass,butnotawrapperclass.Wrapperclasseslike(Integer)existforeachprimitivetype.Theycanbeusedtoconvertaprimitivedatavalueintoanobject,andviceversa.

Q14.Whyjavadoesnothavemultipleinheritances?TheJavadesignteamstrovetomakeJava:Simple,objectoriented,andfamiliarRobustandsecureArchitectureneutralandportableHighperformanceInterpreted,threaded,anddynamicThereasonsforomittingmultipleinheritancefromtheJavalanguagemostlystemfromthe"simple,objectoriented,andfamiliar"goal.Asasimplelanguage,Java'screatorswantedalanguagethatmostdeveloperscouldgraspwithoutextensivetraining.Tothatend,theyworkedtomakethelanguageassimilartoC++aspossible(familiar)withoutcarryingoverC++'sunnecessarycomplexity(simple).Inthedesigners'opinion,multipleinheritancecausesmoreproblemsandconfusionthanitsolves.Sotheycutmultipleinheritancefromthelanguage(justastheycutoperatoroverloading).Thedesigners'extensiveC++experiencetaughtthemthatmultipleinheritancejustwasn'tworththeheadache.

Q15.Whyjavaisnota100%oops?ManypeoplesaythisbecauseJavausesprimitivetypessuchasint,char,double.Butthenalltherestareobjects.Confusingquestion.

Q16.Whatisaresourcebundle?

Initssimplestform,aresourcebundleisrepresentedbyatextfilecontainingkeysandatextvalueforeachkey.*CoreJava*Servlets&JSP*Struts*EJB



*J2ME

Q17.Whatistransientvariable?Transientvariablecan'tbeserialize.ForexampleifavariableisdeclaredastransientinaSerializableclassandtheclassiswrittentoanObjectStream,thevalueofthevariablecan'tbewrittentothestreaminsteadwhentheclassisretrievedfromtheObjectStreamthevalueofthevariablebecomesnull.

Q18.WhatisCollectionAPI?TheCollectionAPIisasetofclassesandinterfacesthatsupportoperationoncollectionsofobjects. These classes and interfaces are more flexible, more powerful, and moreregularthanthevectors,arrays,andhashtablesifeffectivelyreplaces.Exampleofclasses:HashSet,HashMap,ArrayList,LinkedList,TreeSetandTreeMap.Exampleofinterfaces:Collection,Set,ListandMap.

Q19.IsIteratoraClassorInterface?Whatisitsuse?IteratorisaninterfacewhichisusedtostepthroughtheelementsofaCollection.

Q20.Whatissimilarities/differencebetweenanAbstractclassandInterface?Differencesareasfollows:Interfacesprovideaformofmultipleinheritance.Aclasscanextendonlyoneotherclass.Interfacesarelimitedtopublicmethodsandconstantswithnoimplementation.Abstractclassescanhaveapartialimplementation,protectedparts,staticmethods,etc. AClassmay implement several interfaces.But in caseofabstract class,a classmayextendonlyoneabstractclass.Interfacesareslowasitrequiresextraindirectiontotofindcorrespondingmethodinintheactualclass.Abstractclassesarefast.Similarities:NeitherAbstractclassesorInterfacecanbeinstantiated.

Q21.Whatisatransientvariable?Atransientvariableisavariablethatmaynotbeserialized.

Q22.WhichcontainersuseaborderLayoutastheirdefaultlayout?

Thewindow,FrameandDialogclassesuseaborderlayoutastheirdefaultlayout.

Q23.WhydothreadsblockonI/O?Threadsblockoni/o(thatisentersthewaitingstate)sothatotherthreadsmayexecutewhilethei/oOperationisperformed.

Q24.HowareObserverandObservableused?ObjectsthatsubclasstheObservableclassmaintainalistofobservers.WhenanObservableobject is updated it invokes the update () method of each of its observers to notify theobserversthatithaschangedstate.TheObserverinterfaceisimplementedbyobjectsthatobserveObservableobjects.

Q25.Whatissynchronizationandwhyisitimportant?Withrespecttomultithreading,synchronizationisthecapabilitytocontroltheaccessofmultiplethreadstosharedresources.Withoutsynchronization,itispossibleforonethreadtomodifyasharedobjectwhileanotherthreadisintheprocessofusingorupdatingthatobject'svalue.Thisoftenleadstosignificanterrors.

Q26.Canalockbeacquiredonaclass?Yes,alockcanbeacquiredonaclass.Thislockisacquiredontheclass'sClassobject.



Q27.What'snewwiththestop(),suspend()andresume()methodsinJDK1.2?Thestop(),suspend()andresume()methodshavebeendeprecatedinJDK1.2.

Q28.Isnullakeyword?Thenullvalueisnotakeyword.

Q29.Whatisthepreferredsizeofacomponent?Thepreferredsizeofacomponentistheminimumcomponentsizethatwillallowthecomponenttodisplaynormally.

Q30.Whatmethodisusedtospecifyacontainer'slayout?ThesetLayout()methodisusedtospecifyacontainer'slayout.

Q31.WhichcontainersuseaFlowLayoutastheirdefaultlayout?ThePanelandAppletclassesusetheFlowLayoutastheirdefaultlayout.

Q32.Whatstatedoesathreadenterwhenitterminatesitsprocessing?Whenathreadterminatesitsprocessing,itentersthedeadstate.

Q33.WhatistheCollectionsAPI?TheCollectionsAPIisasetofclassesandinterfacesthatsupportoperationsoncollectionsofobjects.

Q34.Whichcharactersmaybeusedasthesecondcharacterofanidentifier,butnotasthefirstcharacterofanidentifier?Thedigits0through9maynotbeusedasthefirstcharacterofanidentifierbuttheymaybeusedafterthefirstcharacterofanidentifier.

Q35.WhatistheListinterface?TheListinterfaceprovidessupportfororderedcollectionsofobjects.

Q36.HowdoesJavahandleintegeroverflowsandunderflows?Itusesthoseloworderbytesoftheresultthatcanfitintothesizeofthetypeallowedbytheoperation.

Q37.WhatistheVectorclass?TheVectorclassprovidesthecapabilitytoimplementagrowablearrayofobjects

Q38.Whatmodifiersmaybeusedwithaninnerclassthatisamemberofanouterclass?A(nonlocal)innerclassmaybedeclaredaspublic,protected,private,static,final,orabstract.

Q39.WhatisanIteratorinterface?TheIteratorinterfaceisusedtostepthroughtheelementsofaCollection.

Q40.Whatisthedifferencebetweenthe>>and>>>operators?The>>operatorcarriesthesignbitwhenshiftingright.The>>>zerofillsbitsthathavebeenshiftedout.

Q41.WhichmethodoftheComponentclassisusedtosetthepositionandsizeofacomponent?setBounds()

Q42.HowmanybitsareusedtorepresentUnicode,ASCII,UTF16,andUTF8



characters?Unicoderequires16bitsandASCIIrequire7bits.AlthoughtheASCIIcharactersetusesonly7bits, it isusuallyrepresentedas8bits.UTF8representscharactersusing8,16,and18bitpatterns.UTF16uses16bitandlargerbitpatterns.

Q43.Whatisthedifferencebetweenyieldingandsleeping?Whenataskinvokesitsyield()method,itreturnstothereadystate.Whenataskinvokesitssleep()method,itreturnstothewaitingstate.

Q44.Whichjava.utilclassesandinterfacessupporteventhandling?TheEventObjectclassandtheEventListenerinterfacesupporteventprocessing.

Q45.Issizeofakeyword?Thesizeofoperatorisnotakeyword.

Q46.Whatarewrappedclasses?Wrappedclassesareclassesthatallowprimitivetypestobeaccessedasobjects.

Q47.Doesgarbagecollectionguaranteethataprogramwillnotrunoutofmemory?Garbage collection doesnot guarantee that a programwill not runout ofmemory. It ispossibleforprogramstouseupmemoryresourcesfasterthantheyaregarbagecollected.Itisalsopossibleforprogramstocreateobjectsthatarenotsubjecttogarbagecollection

Q48.Whatrestrictionsareplacedonthelocationofapackagestatementwithinasourcecodefile?Apackagestatementmustappearasthefirstlineinasourcecodefile(excludingblanklinesandcomments).

Q49.Cananobject'sfinalize()methodbeinvokedwhileitisreachable?Anobject'sfinalize()methodcannotbeinvokedbythegarbagecollectorwhiletheobjectisstillreachable.However,anobject'sfinalize()methodmaybeinvokedbyotherobjects.

Q50.WhatistheimmediatesuperclassoftheAppletclass?Panel

Q51.Whatisthedifferencebetweenpreemptiveschedulingandtimeslicing?Underpreemptivescheduling,thehighestprioritytaskexecutesuntilitentersthewaitingordeadstatesorahigherprioritytaskcomesintoexistence.Undertimeslicing,ataskexecutesforapredefinedsliceoftimeandthenreentersthepoolofreadytasks.Theschedulerthendetermineswhichtaskshouldexecutenext,basedonpriorityandotherfactors.

Q52NamethreeComponentsubclassesthatsupportpainting.TheCanvas,Frame,Panel,andAppletclassessupportpainting.

Q53.WhatvaluedoesreadLine()returnwhenithasreachedtheendofafile?ThereadLine()methodreturnsnullwhenithasreachedtheendofafile.

Q54.WhatistheimmediatesuperclassoftheDialogclass?Window

Q55.Whatisclipping?Clippingistheprocessofconfiningpaintoperationstoalimitedareaorshape.



Q56.Whatisanativemethod?AnativemethodisamethodthatisimplementedinalanguageotherthanJava.

Q57.Canaforstatementloopindefinitely?Yes,forstatementcanloopindefinitely.Forexample,considerthefollowing:for(

Q58.Whatareorderofprecedenceandassociativity,andhowaretheyused?Orderofprecedencedeterminestheorderinwhichoperatorsareevaluatedinexpressions.Associatitydetermineswhetheranexpressionisevaluatedlefttorightorrighttoleft

Q59.WhenathreadblocksonI/O,whatstatedoesitenter?AthreadentersthewaitingstatewhenitblocksonI/O.

Q60.TowhatvalueisavariableoftheStringtypeautomaticallyinitialized?ThedefaultvalueofaStringtypeisnull.

Q61.Whatisthecatchordeclareruleformethoddeclarations?Ifacheckedexceptionmaybethrownwithinthebodyofamethod,themethodmusteithercatchtheexceptionordeclareitinitsthrowsclause.

Q62.WhatisthedifferencebetweenaMenuItemandaCheckboxMenuItem?TheCheckboxMenuItemclassextendstheMenuItemclasstosupportamenuitemthatmaybecheckedorunchecked.

Q63.Whatisatask'spriorityandhowisitusedinscheduling?Atask'spriorityisanintegervaluethatidentifiestherelativeorderinwhichitshouldbeexecutedwithrespecttoothertasks.Theschedulerattemptstoschedulehigherprioritytasksbeforelowerprioritytasks.

Q64.WhatclassisthetopoftheAWTeventhierarchy?Thejava.awt.AWTEventclassisthehighestlevelclassintheAWTeventclasshierarchy.

Q65.Whenathreadiscreatedandstarted,whatisitsinitialstate?Athreadisinthereadystateafterithasbeencreatedandstarted.

Q66.Canananonymousclassbedeclaredasimplementinganinterfaceandextendingaclass?Ananonymousclassmayimplementaninterfaceorextendasuperclass,butmaynotbedeclaredtodoboth.

Q67.Whatistherangeoftheshorttype?Therangeoftheshorttypeis(2^15)to2^151.

Q68.Whatistherangeofthechartype?Therangeofthechartypeis0to2^161.

Q69.InwhichpackagearemostoftheAWTeventsthatsupporttheeventdelegationmodeldefined?MostoftheAWTrelatedeventsoftheeventdelegationmodelaredefinedinthejava.awt.eventpackage.TheAWTEventclassisdefinedinthejava.awtpackage.



Q70.WhatistheimmediatesuperclassofMenu?MenuItem

Q71.Whatisthepurposeoffinalization?Thepurposeoffinalizationistogiveanunreachableobjecttheopportunitytoperformanycleanupprocessingbeforetheobjectisgarbagecollected.

Q72.WhichclassistheimmediatesuperclassoftheMenuComponentclass.Object

Q73.Whatinvokesathread'srun()method?Afterathreadisstarted,viaitsstart()methodorthatoftheThreadclass,theJVMinvokesthethread'srun()methodwhenthethreadis

initiallyexecuted.

Q74.WhatisthedifferencebetweentheBoolean&operatorandthe&&operator?IfanexpressioninvolvingtheBoolean&operatorisevaluated,bothoperandsareevaluated.Thenthe&operatorisappliedtotheoperand.Whenanexpressioninvolvingthe&&operatorisevaluated,thefirstoperandisevaluated.Ifthefirstoperandreturnsavalueoftruethenthesecondoperandisevaluated.The&&operatoristhenappliedtothefirstandsecondoperands.Ifthefirstoperandevaluatestofalse,theevaluationofthesecondoperandisskipped.

Q75.NamethreesubclassesoftheComponentclass.Box.Filler,Button,Canvas,Checkbox,Choice,Container,Label,List,Scrollbar,orTextComponent.

Q76.WhatistheGregorianCalendarclass?TheGregorianCalendarprovidessupportfortraditionalWesterncalendars.

Q77.WhichContainermethodisusedtocauseacontainertobelaidoutandredisplayed?validate()

Q78.WhatisthepurposeoftheRuntimeclass?ThepurposeoftheRuntimeclassistoprovideaccesstotheJavaruntimesystem.

Q79.Howmanytimesmayanobject'sfinalize()methodbeinvokedbythegarbagecollector?Anobject'sfinalize()methodmayonlybeinvokedoncebythegarbagecollector.

Q80.Whatisthepurposeofthefinallyclauseofatrycatchfinallystatement?Thefinallyclauseisusedtoprovidethecapabilitytoexecutecodenomatterwhetherornotanexceptionisthrownorcaught.

Q81.Whatistheargumenttypeofaprogram'smain()method?Aprogram'smain()methodtakesanargumentoftheString[]type.



Q82.WhichJavaoperatorisrightassociative?

The=operatorisrightassociative.

Q83.WhatistheLocaleclass?TheLocaleclassisusedtotailorprogramoutputtotheconventionsofaparticulargeographic,political,orculturalregion.

Q84.Canadoublevaluebecasttoabyte?Yes,adoublevaluecanbecasttoabyte.

Q85.Whatisthedifferencebetweenabreakstatementandacontinuestatement?Abreakstatementresultsintheterminationofthestatementtowhichitapplies(switch,for,do, or while). A continue statement is used to end the current loop iteration and returncontroltotheloopstatement.

Q86.Whatmustaclassdotoimplementaninterface?Itmustprovideallofthemethodsintheinterfaceandidentifytheinterfaceinitsimplementsclause.

Q87.Whatmethodisinvokedtocauseanobjecttobeginexecutingasaseparatethread?Thestart()methodoftheThreadclassisinvokedtocauseanobjecttobeginexecutingasaseparatethread.

Q88.NametwosubclassesoftheTextComponentclass.TextFieldandTextArea

Q89.Whatistheadvantageoftheeventdelegationmodelovertheearliereventinheritancemodel?Theeventdelegationmodelhastwoadvantagesovertheeventinheritancemodel.First,itenableseventhandlingtobehandledbyobjectsotherthantheonesthatgeneratetheevents(ortheircontainers).Thisallowsacleanseparationbetweenacomponent'sdesignanditsuse.Theotheradvantageoftheeventdelegationmodelisthatitperformsmuchbetterinapplicationswheremanyeventsaregenerated.Thisperformanceimprovementisduetothefactthattheeventdelegationmodeldoesnothavetorepeatedlyprocessunhandledevents,asisthecaseoftheeventinheritancemodel.

Q90.WhichcontainersmayhaveaMenuBar?Frame

Q91.Howarecommasusedintheintializationanditerationpartsofaforstatement?Commasareusedtoseparatemultiplestatementswithintheinitialization

anditerationpartsofaforstatement.

Q92.Whatisthepurposeofthewait(),notify(),andnotifyAll()methods?Thewait(),notify(),andnotifyAll()methodsareusedtoprovideanefficientwayforthreadstowaitforasharedresource.Whenathreadexecutesanobject'swait()



method,itentersthewaitingstate.Itonlyentersthereadystateafteranotherthreadinvokestheobject'snotify()ornotifyAll()methods..

Q93.Whatisanabstractmethod?Anabstractmethodisamethodwhoseimplementationisdeferredtoasubclass.

Q94.HowareJavasourcecodefilesnamed?AJavasourcecodefiletakesthenameofapublicclassorinterfacethatisdefinedwithinthefile.Asourcecodefilemaycontainatmostonepublicclassorinterface.Ifapublicclassorinterfaceisdefinedwithinasourcecodefile,thenthesourcecodefilemusttakethenameofthepublicclassorinterface.Ifnopublicclassorinterfaceisdefinedwithinasourcecodefile,thenthefilemusttakeonanamethatisdifferentthanitsclassesandinterfaces.Sourcecodefilesusethe.javaextension.

Q95.WhatistherelationshipbetweentheCanvasclassandtheGraphicsclass?ACanvasobjectprovidesaccesstoaGraphicsobjectviaitspaint()method.

Q96.Whatarethehighlevelthreadstates?Thehighlevelthreadstatesareready,running,waiting,anddead.

Q97.Whatvaluedoesread()returnwhenithasreachedtheendofafile?Theread()methodreturns1whenithasreachedtheendofafile.

Q98.CanaByteobjectbecasttoadoublevalue?No,anobjectcannotbecasttoaprimitivevalue.

Q99.Whatisthedifferencebetweenastaticandanonstaticinnerclass?Anonstaticinnerclassmayhaveobjectinstancesthatareassociatedwithinstancesoftheclass'souterclass.Astaticinnerclassdoesnothaveanyobjectinstances.

Q100.WhatisthedifferencebetweentheStringandStringBufferclasses?Stringobjectsareconstants.StringBufferobjectsarenot.

Q101.Ifavariableisdeclaredasprivate,wheremaythevariablebeaccessed?Aprivatevariablemayonlybeaccessedwithintheclassinwhichitisdeclared.

Q102.Whatisanobject'slockandwhichobject'shavelocks?Anobject's lock is amechanism that is usedbymultiple threads to obtain synchronizedaccesstotheobject.Athreadmayexecuteasynchronizedmethodofanobjectonlyafterithasacquiredtheobject'slock.Allobjectsandclasseshavelocks.Aclass'slockisacquiredontheclass'sClassobject.

Q103.WhatistheDictionaryclass?TheDictionaryclassprovidesthecapabilitytostorekeyvaluepairs.

Q104.HowaretheelementsofaBorderLayoutorganized?TheelementsofaBorderLayoutareorganizedattheborders(North,South,East,andWest)andthecenterofacontainer.



Q105.Whatisthe%operator?Itisreferredtoasthemoduloorremainderoperator.Itreturnstheremainderofdividingthefirstoperandbythesecondoperand.

Q106.Whencananobjectreferencebecasttoaninterfacereference?Anobjectreferencebecasttoaninterfacereferencewhentheobjectimplementsthereferencedinterface.Q107.WhatisthedifferencebetweenaWindowandaFrame?TheFrameclassextendsWindowtodefineamainapplicationwindowthatcanhaveamenubar.

Q108.Whichclassisextendedbyallotherclasses?TheObjectclassisextendedbyallotherclasses.

Q109.Cananobjectbegarbagecollectedwhileitisstillreachable?Areachableobjectcannotbegarbagecollected.Onlyunreachableobjectsmaybegarbagecollected..

Q110.Istheternaryoperatorwrittenx:y?zorx?y:z?Itiswrittenx?y:z.

Q111.WhatisthedifferencebetweentheFontandFontMetricsclasses?TheFontMetricsclassisusedtodefineimplementationspecificproperties,suchasascentanddescent,ofaFontobject.

Q112.Howisroundingperformedunderintegerdivision?Thefractionalpartoftheresultistruncated.Thisisknownasroundingtowardzero.

Q113.Whathappenswhenathreadcannotacquirealockonanobject?Ifathreadattemptstoexecuteasynchronizedmethodorsynchronizedstatementandisunable to acquire an object's lock, it enters the waiting state until the lock becomesavailable.

Q114.WhatisthedifferencebetweentheReader/WriterclasshierarchyandtheInputStream/OutputStreamclasshierarchy?TheReader/Writerclasshierarchyischaracteroriented,andtheInputStream/OutputStreamclasshierarchyisbyteoriented.

Q115.Whatclassesofexceptionsmaybecaughtbyacatchclause?AcatchclausecancatchanyexceptionthatmaybeassignedtotheThrowabletype.ThisincludestheErrorandExceptiontypes.

Q116.Ifaclassisdeclaredwithoutanyaccessmodifiers,wheremaytheclassbeaccessed?Aclassthatisdeclaredwithoutanyaccessmodifiersissaidtohavepackageaccess.Thismeansthattheclasscanonlybeaccessedbyotherclassesandinterfacesthataredefinedwithinthesamepackage.

Q117.WhatistheSimpleTimeZoneclass?TheSimpleTimeZoneclassprovidessupportforaGregoriancalendar.

Q118.WhatistheMapinterface?TheMapinterfacereplacestheJDK1.1Dictionaryclassandisusedassociatekeyswithvalues.



Q119.Doesaclassinherittheconstructorsofitssuperclass?Aclassdoesnotinheritconstructorsfromanyofitssuperclasses.

Q120.Forwhichstatementsdoesitmakesensetousealabel?Theonlystatementsforwhichitmakessensetousealabelarethosestatementsthatcanencloseabreakorcontinuestatement.

Q121.WhatisthepurposeoftheSystemclass?

ThepurposeoftheSystemclassistoprovideaccesstosystemresources.

Q122.WhichTextComponentmethodisusedtosetaTextComponenttothereadonlystate?setEditable()

Q123.HowaretheelementsofaCardLayoutorganized?TheelementsofaCardLayoutarestacked,oneontopoftheother,likeadeckofcards.

Q124.Is&&=avalidJavaoperator?No,itisnot.

Q125.NametheeightprimitiveJavatypes?Theeightprimitivetypesarebyte,char,short,int,long,float,double,andboolean.

Q126.Whichclassshouldyouusetoobtaindesigninformationaboutanobject?TheClassclassisusedtoobtaininformationaboutanobject'sdesign.

Q127.Whatistherelationshipbetweenclippingandrepainting?WhenawindowisrepaintedbytheAWTpaintingthread,itsetstheclippingregionstotheareaofthewindowthatrequiresrepainting.

Q128.Is"abc"aprimitivevalue?TheStringliteral"abc"isnotaprimitivevalue.ItisaStringobject.

Q129.Whatistherelationshipbetweenaneventlistenerinterfaceandaneventadapterclass?Aneventlistenerinterfacedefinesthemethodsthatmustbeimplementedbyaneventhandlerforaparticularkindofevent.Aneventadapterprovidesadefaultimplementationofaneventlistenerinterface.

Q130.Whatrestrictionsareplacedonthevaluesofeachcaseofaswitchstatement?Duringcompilation,thevaluesofeachcaseofaswitchstatementmustevaluatetoavaluethatcanbepromotedtoanintvalue.

Q131.Whatmodifiersmaybeusedwithaninterfacedeclaration?Aninterfacemaybedeclaredaspublicorabstract.

Q132.Isaclassasubclassofitself?Aclassisasubclassofitself.

Q133.Whatisthehighestleveleventclassoftheeventdelegationmodel?

Thejava.util.EventObjectclassisthehighestlevelclassintheeventdelegationclasshierarchy.



Q134.Whateventresultsfromtheclickingofabutton?TheActionEventeventisgeneratedastheresultoftheclickingofabutton.

Q135.HowcanaGUIcomponenthandleitsownevents?Acomponentcanhandleitsowneventsbyimplementingtherequiredeventlistenerinterfaceandaddingitselfasitsowneventlistener.

Q136.Whatisthedifferencebetweenawhilestatementandadostatement?A while statement checks at the beginning of a loop to see whether the next loopiterationshouldoccur.Adostatementchecksat theendofa loop toseewhether thenextiterationofaloopshouldoccur.Thedostatementwillalwaysexecutethebodyofaloopatleastonce.

Q137.HowaretheelementsofaGridBagLayoutorganized?TheelementsofaGridBagLayoutareorganizedaccordingtoagrid.However,theelementsareofdifferentsizesandmayoccupymorethanoneroworcolumnofthegrid.Inaddition,therowsandcolumnsmayhavedifferentsizes.

Q138.WhatadvantagedoJava'slayoutmanagersprovideovertraditionalwindowingsystems?Java uses layout managers to lay out components in a consistent manner across allwindowing platforms. Since Java's layout managers aren't tied to absolute sizing andpositioning, they are able to accomodate platformspecific differences amongwindowingsystems.

Q139.WhatistheCollectioninterface?TheCollectioninterfaceprovidessupportfortheimplementationofamathematicalbaganunorderedcollectionofobjectsthatmaycontainduplicates.

Q140.Whatmodifierscanbeusedwithalocalinnerclass?Alocalinnerclassmaybefinalorabstract.

Q141.Whatisthedifferencebetweenstaticandnonstaticvariables?Astaticvariableisassociatedwiththeclassasawholeratherthanwithspecificinstancesofaclass.Nonstaticvariablestakeonuniquevalueswitheachobjectinstance.

Q142.Whatisthedifferencebetweenthepaint()andrepaint()methods?Thepaint()methodsupportspaintingviaaGraphicsobject.Therepaint()methodisusedtocausepaint()tobeinvokedbytheAWTpaintingthread.

Q143.WhatisthepurposeoftheFileclass?TheFileclassisusedtocreateobjectsthatprovideaccesstothefilesanddirectoriesofalocalfilesystem.

Q144.Cananexceptionberethrown?Yes,anexceptioncanberethrown.

Q145.WhichMathmethodisusedtocalculatetheabsolutevalueofanumber?Theabs()methodisusedtocalculateabsolutevalues.



Q146.HowdoesmultithreadingtakeplaceonacomputerwithasingleCPU?Theoperatingsystem'staskschedulerallocatesexecutiontimetomultipletasks.Byquicklyswitchingbetweenexecutingtasks,itcreatestheimpressionthattasksexecutesequentially.

Q147.Whendoesthecompilersupplyadefaultconstructorforaclass?Thecompilersuppliesadefaultconstructorforaclassifnootherconstructorsareprovided.

Q148.Whenisthefinallyclauseofatrycatchfinallystatementexecuted?Thefinallyclauseofthetrycatchfinallystatementisalwaysexecutedunlessthethreadofexecutionterminatesoranexceptionoccurswithintheexecutionofthefinallyclause.

Q149.WhichclassistheimmediatesuperclassoftheContainerclass?Component

Q150.Ifamethodisdeclaredasprotected,wheremaythemethodbeaccessed?Aprotectedmethodmayonlybeaccessedbyclassesorinterfacesofthesamepackageorbysubclassesoftheclassinwhichitisdeclared.

Q151.HowcantheCheckboxclassbeusedtocreatearadiobutton?ByassociatingCheckboxobjectswithaCheckboxGroup.

Q152.WhichnonUnicodelettercharactersmaybeusedasthefirstcharacterofanidentifier?ThenonUnicodelettercharacters$and_mayappearasthefirstcharacterofanidentifier

Q153.Whatrestrictionsareplacedonmethodoverloading?Twomethodsmaynothavethesamenameandargumentlistbutdifferentreturntypes.

Q154.Whathappenswhenyouinvokeathread'sinterruptmethodwhileitissleepingorwaiting?Whenatask'sinterrupt()methodisexecuted,thetaskentersthereadystate.Thenexttimethetaskenterstherunningstate,anInterruptedExceptionisthrown.

Q155.Whatiscasting?Therearetwotypesofcasting,castingbetweenprimitivenumerictypesandcastingbetweenobjectreferences.Castingbetweennumerictypesisusedtoconvertlargervalues,suchasdoublevalues,tosmallervalues,suchasbytevalues.Castingbetweenobjectreferencesisusedtorefertoanobjectbyacompatibleclass,interface,orarraytypereference.

Q156.Whatisthereturntypeofaprogram'smain()method?Aprogram'smain()methodhasavoidreturntype.

Q157.NamefourContainerclasses.Window,Frame,Dialog,FileDialog,Panel,Applet,orScrollPane

Q158.WhatisthedifferencebetweenaChoiceandaList?



AChoiceisdisplayedinacompactformthatrequiresyoutopullitdowntoseethelistofavailablechoices.OnlyoneitemmaybeselectedfromaChoice.AListmaybedisplayedinsuchawaythatseveralListitemsarevisible.AListsupportstheselectionofoneormoreListitems.

Q159.WhatclassofexceptionsaregeneratedbytheJavaruntimesystem?

TheJavaruntimesystemgeneratesRuntimeExceptionandErrorexceptions.

Q160.Whatclassallowsyoutoreadobjectsdirectlyfromastream?TheObjectInputStreamclasssupportsthereadingofobjectsfrominputstreams.

Q161.Whatisthedifferencebetweenafieldvariableandalocalvariable?Afieldvariableisavariablethatisdeclaredasamemberofaclass.Alocalvariableisavariablethatisdeclaredlocaltoamethod.

Q162.Underwhatconditionsisanobject'sfinalize()methodinvokedbythegarbagecollector?Thegarbagecollectorinvokesanobject'sfinalize()methodwhenitdetectsthattheobjecthasbecomeunreachable.

Q163.Howarethis()andsuper()usedwithconstructors?

this()isusedtoinvokeaconstructorofthesameclass.super()isusedtoinvokeasuperclassconstructor.

Q164.Whatistherelationshipbetweenamethod'sthrowsclauseandtheexceptionsthatcanbethrownduringthemethod'sexecution?

Amethod'sthrowsclausemustdeclareanycheckedexceptionsthatarenotcaughtwithinthebodyofthemethod.

Q165.WhatisthedifferencebetweentheJDK1.02eventmodelandtheeventdelegationmodelintroducedwithJDK1.1?

TheJDK1.02eventmodelusesaneventinheritanceorbubblingapproach.Inthismodel,componentsarerequiredtohandletheirownevents.Iftheydonothandleaparticularevent,theeventisinheritedby(orbubbledupto)thecomponent'scontainer.Thecontainertheneitherhandlestheeventoritisbubbleduptoitscontainerandsoon,untilthehighestlevelcontainerhasbeentried..Intheeventdelegationmodel,specificobjectsaredesignatedaseventhandlersforGUIcomponents.Theseobjectsimplementeventlistenerinterfaces.Theeventdelegationmodelismoreefficientthantheeventinheritancemodelbecauseiteliminatestheprocessingrequiredtosupportthebubblingofunhandledevents.

Q166.HowisitpossiblefortwoStringobjectswithidenticalvaluesnottobeequalunderthe==operator?The==operatorcomparestwoobjectstodetermineiftheyarethesameobjectinmemory.Itis



possiblefortwoStringobjectstohavethesamevalue,butlocatedindifferentareasofmemory.

Q167.WhyarethemethodsoftheMathclassstatic?Sotheycanbeinvokedasiftheyareamathematicalcodelibrary.

Q168.WhatCheckboxmethodallowsyoutotellifaCheckboxischecked?getState()Q169.Whatstateisathreadinwhenitisexecuting?Anexecutingthreadisintherunningstate.

Q170.Whatarethelegaloperandsoftheinstanceofoperator?Theleftoperandisanobjectreferenceornullvalueandtherightoperandisaclass,interface,orarraytype.

Q171.HowaretheelementsofaGridLayoutorganized?TheelementsofaGridBadlayoutareofequalsizeandarelaidoutusingthesquaresofagrid.

Q172.WhatanI/Ofilter?AnI/Ofilterisanobjectthatreadsfromonestreamandwritestoanother,usuallyalteringthedatainsomewayasitispassedfromonestreamtoanother.

Q173.Ifanobjectisgarbagecollected,canitbecomereachableagain?Onceanobjectisgarbagecollected,itceasestoexist.Itcannolongerbecomereachableagain.

Q174.WhatistheSetinterface?TheSetinterfaceprovidesmethodsforaccessingtheelementsofafinitemathematicalset.Setsdonotallowduplicateelements.

Q175.Whatclassesofexceptionsmaybethrownbyathrowstatement?AthrowstatementmaythrowanyexpressionthatmaybeassignedtotheThrowabletype.

Q176.WhatareEandPI?EisthebaseofthenaturallogarithmandPIismathematicalvaluepi.

Q177.Aretrueandfalsekeywords?Thevaluestrueandfalsearenotkeywords.

Q178.Whatisavoidreturntype?Avoidreturntypeindicatesthatamethoddoesnotreturnavalue.

Q179.WhatisthepurposeoftheenableEvents()method?TheenableEvents()methodisusedtoenableaneventforaparticularobject.Normally,aneventisenabledwhenalistenerisaddedtoanobjectforaparticularevent.TheenableEvents()methodisusedbyobjectsthathandleeventsbyoverridingtheireventdispatchmethods.

Q180.WhatisthedifferencebetweentheFileandRandomAccessFileclasses?TheFileclassencapsulatesthefilesanddirectoriesofthelocalfilesystem.TheRandomAccessFileclassprovidesthemethodsneededtodirectlyaccessdatacontainedinanypartofafile.



Q181.WhathappenswhenyouaddadoublevaluetoaString?TheresultisaStringobject.

Q182.Whatisyourplatform'sdefaultcharacterencoding?IfyouarerunningJavaonEnglishWindowsplatforms,itisprobablyCp1252.IfyouarerunningJavaonEnglishSolarisplatforms,itismostlikely8859_1..

Q183.Whichpackageisalwaysimportedbydefault?Thejava.langpackageisalwaysimportedbydefault.

Q184.Whatinterfacemustanobjectimplementbeforeitcanbewrittentoastreamasanobject?AnobjectmustimplementtheSerializableorExternalizableinterfacebeforeitcanbewrittentoastreamasanobject.

Q185.Howarethisandsuperused?thisisusedtorefertothecurrentobjectinstance.superisusedtorefertothevariablesandmethodsofthesuperclassofthecurrentobjectinstance.

Q186.Whatisthepurposeofgarbagecollection?Thepurposeofgarbagecollectionistoidentifyanddiscardobjectsthatarenolongerneededbyaprogramsothattheirresourcesmaybereclaimedandreused.

Q187.Whatisacompilationunit?AcompilationunitisaJavasourcecodefile.

Q188.WhatinterfaceisextendedbyAWTeventlisteners?AllAWTeventlistenersextendthejava.util.EventListenerinterface.

Q189.Whatrestrictionsareplacedonmethodoverriding?Overriddenmethodsmusthavethesamename,argumentlist,andreturntype.Theoverridingmethodmaynotlimittheaccessofthemethoditoverrides. Theoverridingmethodmaynot throwanyexceptions thatmaynot be thrownby theoverriddenmethod.

Q190.Howcanadeadthreadberestarted?Adeadthreadcannotberestarted.

Q191.Whathappensifanexceptionisnotcaught?AnuncaughtexceptionresultsintheuncaughtException()methodofthethread'sThreadGroupbeinginvoked,whicheventuallyresultsintheterminationoftheprograminwhichitisthrown.

Q192.Whatisalayoutmanager?Alayoutmanagerisanobjectthatisusedtoorganizecomponentsinacontainer.

Q193.WhicharithmeticoperationscanresultinthethrowingofanArithmeticException?Integer/and%canresultinthethrowingofanArithmeticException.



Q194.Whatarethreewaysinwhichathreadcanenterthewaitingstate?Athreadcanenterthewaitingstatebyinvokingitssleep()method,byblockingonI/O,byunsuccessfully attempting to acquire an object's lock, or by invoking an object's wait()method.Itcanalsoenterthewaitingstatebyinvokingits(deprecated)suspend()method.

Q195.Cananabstractclassbefinal?Anabstractclassmaynotbedeclaredasfinal.

Q196.WhatistheResourceBundleclass?TheResourceBundleclassisusedtostorelocalespecificresourcesthatcanbeloadedbyaprogramtotailortheprogram'sappearancetotheparticularlocaleinwhichitisbeingrun.

Q197.Whathappensifatrycatchfinallystatementdoesnothaveacatchclausetohandleanexceptionthatisthrownwithinthebodyofthetrystatement?Theexceptionpropagatesuptothenexthigherleveltrycatchstatement(ifany)orresultsintheprogram'stermination.

Q198.Whatisnumericpromotion?Numericpromotionistheconversionofasmallernumerictypetoalargernumerictype,sothatintegerandfloatingpointoperationsmaytakeplace.Innumericalpromotion,byte,char,andshortvaluesareconvertedtointvalues.Theintvaluesarealsoconvertedtolongvalues,ifnecessary.Thelongandfloatvaluesareconvertedtodoublevalues,asrequired.

Q199.WhatisthedifferencebetweenaScrollbarandaScrollPane?AScrollbarisaComponent,butnotaContainer.AScrollPaneisaContainer.AScrollPanehandlesitsowneventsandperformsitsownscrolling.

Q200.Whatisthedifferencebetweenapublicandanonpublicclass?Apublicclassmaybeaccessedoutsideofitspackage.Anonpublicclassmaynotbeaccessedoutsideofitspackage.

Q201.Towhatvalueisavariableofthebooleantypeautomaticallyinitialized?Thedefaultvalueofthebooleantypeisfalse.

Q202.Cantrystatementsbenested?Trystatementsmaybetested.

Q203.Whatisthedifferencebetweentheprefixandpostfixformsofthe++operator?Theprefixformperformstheincrementoperationandreturnsthevalueoftheincrementoperation.Thepostfixformreturnsthecurrentvaluealloftheexpressionandthenperformstheincrementoperationonthatvalue.

Q204.Whatisthepurposeofastatementblock?Astatementblockisusedtoorganizeasequenceofstatementsasasinglestatementgroup.

Q205.WhatisaJavapackageandhowisitused?AJavapackageisanamingcontextforclassesandinterfaces.Apackageisusedtocreatea



separatenamespaceforgroupsofclassesandinterfaces.PackagesarealsousedtoorganizerelatedclassesandinterfacesintoasingleAPIunitandtocontrolaccessibilitytotheseclassesandinterfaces.

Q206.Whatmodifiersmaybeusedwithatoplevelclass?Atoplevelclassmaybepublic,abstract,orfinal.

Q207.WhataretheObjectandClassclassesusedfor?TheObjectclassisthehighestlevelclassintheJavaclasshierarchy.TheClassclassisusedtorepresenttheclassesandinterfacesthatareloadedbyaJavaprogram..

Q208.Howdoesatrystatementdeterminewhichcatchclauseshouldbeusedtohandleanexception?Whenanexceptionisthrownwithinthebodyofatrystatement,thecatchclausesofthetrystatementareexaminedintheorderinwhichtheyappear.Thefirstcatchclausethatiscapableofhandlingtheexceptionisexecuted.Theremainingcatchclausesareignored.

Q209.Cananunreachableobjectbecomereachableagain?Anunreachableobjectmaybecomereachableagain.Thiscanhappenwhentheobject'sfinalize()methodisinvokedandtheobjectperformsanoperationwhichcausesittobecomeaccessibletoreachableobjects.

Q210.Whenisanobjectsubjecttogarbagecollection?Anobjectissubjecttogarbagecollectionwhenitbecomesunreachabletotheprograminwhichitisused.

Q211.Whatmethodmustbeimplementedbyallthreads?Alltasksmustimplementtherun()method,whethertheyareasubclassofThreadorimplementtheRunnableinterface.

Q212.WhatmethodsareusedtogetandsetthetextlabeldisplayedbyaButtonobject?getLabel()andsetLabel()

Q213.WhichComponentsubclassisusedfordrawingandpainting?Canvas

Q214.Whataresynchronizedmethodsandsynchronizedstatements?

Synchronizedmethodsaremethodsthatareusedtocontrolaccesstoanobject.Athreadonlyexecutesasynchronizedmethodafterithasacquiredthelockforthemethod'sobjectorclass.Synchronizedstatementsaresimilartosynchronizedmethods.Asynchronizedstatementcanonlybeexecutedafterathreadhasacquiredthelockfortheobjectorclassreferencedinthesynchronizedstatement.

Q215.Whatarethetwobasicwaysinwhichclassesthatcanberunasthreadsmaybedefined?AthreadclassmaybedeclaredasasubclassofThread,oritmayimplementtheRunnableinterface.

Q216.WhataretheproblemsfacedbyJavaprogrammerswhodon'tuselayoutmanagers?Withoutlayoutmanagers,JavaprogrammersarefacedwithdetermininghowtheirGUIwillbedisplayedacrossmultiplewindowingsystemsandfindingacommonsizingand



positioningthatwillworkwithintheconstraintsimposedbyeachwindowingsystem.

Q217.Whatisthedifferencebetweenanifstatementandaswitchstatement?

Theifstatementisusedtoselectamongtwoalternatives.Itusesabooleanexpressiontodecidewhichalternativeshouldbeexecuted.Theswitchstatementisusedtoselectamongmultiplealternatives.Itusesanintexpressiontodeterminewhichalternativeshouldbeexecuted.

Q218.WhathappenswhenyouaddadoublevaluetoaString?TheresultisaStringobject.

Q219.WhatistheListinterface?TheListinterfaceprovidessupportfororderedcollectionsofobjects

Q220.WhatisanException?Ans.Anunwanted,unexpectedeventthatdisturbsnormalflowoftheprogramiscalledException.Example:FileNotFondException.

Q221.WhatisthepurposeofExceptionHandling?Ans.ThemainpurposeofExceptionHandlingisforgracefulterminationoftheprogram.

Q222.WhatisthemeaningofExceptionHandling?Ans.ExceptionHandlingdoesntmeanrepairinganException,wehavetodefinealternativewaytocontinuerestofthecodenormally.Example:IfourprogrammingrequirementistoreadthedatafromthefilelocatingatLondonbutatRuntimeifLondonfileisnotavailablethenwehavetouselocalfilealternativelytocontinuerestofprogramnormally.ThisisnothingbutExceptionHandling.

Q223.ExplainDefaultExceptionHandlingMechanisminjava?

Ans.Ifanexceptionraised,themethodinwhichitsraisedisresponsibleforthecreationofExceptionsobjectbyincludingthefollowinginformation:NameoftheExceptionDescriptionoftheExceptionStackTraceAftercreatingExceptionobjectthemethodhandoverittotheJVM.JVMchecksforExceptionHandlingcodeinthatmethod.IfthemethoddoesntcontainanyExceptionhandlingcodethenJVMterminatesthemethodabnormallyandremovesthecorrespondingentryfromthestack.JVMidentifythecallermethodandchecksforExceptionHandlingcodeinthatmethod.IfthecallerdoesntcontainanyexceptionhandlingcodethenJVMterminatesthatmethodabnormallyandremovesthecorrespondingentryfromthestack.Thisprocesswillbecontinueuntilmain()method.Ifthemain()methodalsodoesntcontainexceptionhandlingcodetheJVMterminatesthatmain()methodandremovesthecorrespondingentryfromthestack.JustbeforeterminatingtheprogramabnormallyJVMhandoverstheresponsibilityofexceptionhandlingtotheDefaultExceptionHandlerwhichisthecomponentofJVM.DefaultExceptionHandlerjustprintexceptioninformationtotheconsolinthefollowingformat

NameofException:DescriptionStackTrace(LocationoftheException)

Q224.Whatisthepurposeoftry?AnsWeshouldmaintainallriskycodeinsidethetryblock.



Q225.Whatisthepurposeofcatchblock?Ans.WehavetomaintainallExceptionHandlingcodeinsidethecatchblock.

Q226.Istrywithmultiplecatchblockispossible?Ans.Thewayofhandlinganexceptionisvariedfromexceptiontoexceptioncompulsorywehavetowriteaseparatecatchblockforeveryexception.Hencetrywillmultiplecatchblockispossibleanditisrecommendedtouse.Example:try{//Riskycode}catch(IOExceptione){//HndlingcodeforIOException

}catch(ArithmeticExceptione){//handlingcodeforAE}catch(NullPointerExcetpione){//handlingcodeforNPE}catch(Exceptione){//defaultexceptionhandlingcode}

Q227.Iftrywithmultiplecatchblockpresentisorderofcatchblocksimportantinwhichorderwehavetotake?Ans.Iftrywithmultiplecatchblockpresentthentheorderofcatchblockisveryimportantitshouldbefromchildtoparentbutnotfromparenttochild.

Q228.WhatarevariousmethodstoprintExceptioninformation?anddifferentiatethem.Ans.Throwableclassdefinesthefollowingmethodtoprintexceptionorerrorinformation.1.printStackTrace():Thismethodprintexceptioninformationinthefollowingformat.NameoftheException:DescriptionStackTrace2.toString():Thismethodprintexceptioninformationinthefollowingformat.NameoftheException:Description3.getMessage():Thismethodprintsonlydescriptionoftheexception.Description

Q229.Ifanexceptionrisedinsidecatchblockthenwhatwillhappen?Ans.Ifanexceptionraisedinsidecatchblockanditisnotpartofanytryblockthenitisalwaysabnormaltermination.

Q230.Isitpossibletotaketry,catchinsidetryblock?Ans.Yes,Itispossibletotaketry,catchinsidetryblock.Thatisnestingoftrycatchispossible.



Q231.Isitpossibletotaketry,catchinsidecatchblock?Ans.Yes,Itispossibletotaketry,catchinsidecatchblock.

Q232.Isitpossibletotaketrywithoutcatch?Ans.Yes,itispossibletotaketrywithoutcatchbutcompulsoryfinallyblockshouldbeavailable.

Q233.Whatisthepurposeoffinallyblock?Ans.Themainpurposeoffinallyblockis,tomaintainthecleanupcode.Thisblockwillexecutealways.

Q234.Isfinallyblockwillbeexecutealways?Ans.Yesfinallyblockwillbeexecutedalwaysirrespectiveofwhetherexceptionraisedornotraisedwhetherexceptionsarehandledornothandle.ThereisonesituationwherethefinallyblockwontbeexecutediftheJVMisgoingtobeshutdown.

Q235.Inwhichsituationfinallyblockwillnotexecuted?Ans.Thereisonesituationwherethefinallyblockwontbeexecutedifweareusingsystem.exit(0)explicitlythenJVMitselfwillbeshutdownandthereisnochanceofexecutingfinallyblock.

Q236.Ifreturnstatementpresentinsidetryisfinallyblockwillbeexecuted?Ans.Yes,ifreturnstatementpresentinsidetry,thenalsofinallyblockwillbeexecuted.finallyblockwilldominatereturnstatementalso.

Q237.Whatisthedifferencebetweenfinal,finallyandfinalize()?Ans.final:finalisamodifierapplicableforvariables,methodsandclasses.finalvariablemeansconstantandreassignment isnotpossible.finalmethodmeansimplementationis final in the child classeswe cant override. final classmeans itwont participate ininheritanceandchildclasscreationisnotpossible.finally:Itisablockassociatedwithtrycatchtomaintaincleanupcode.Finallyblockwillbeexecutedalwaysirrespectiveofwhetherexceptionisraisedornotraisedorwhethertheexceptionishandleornothandle.finalize():Itisamethod,Garbagecollectoralwayscallsthismethodjustbeforedestroyinganyobjecttoperformcleanupactivities.

Q238.Isitpossibletowriteanystatementbetweentrycatchandfinally?Ans.No,itisnotpossibletowriteanystatementbetweentrycatchandfinally.Ifwewilltrytowriteanystatementbetweenthemthenwewillgetcompiletimeerror.

Q239.Isitpossibletotaketwofinallyblocksforthesametry?Ans.No,itisnotpossibletotaketwofinallyblocksforthesametry.Ifwetrytotakethenwewillgetcompiletimeerror.

Q240.Issyntaxtryfinallycatchisvalid?Ans.No,thissyntaxisnotvalid.Itshouldbeliketrycatchfinallythenonlycodewillcompile.

Q241.Whatisthepurposeofthrow?Ans.SometimeswecancreateExceptionobjectexplicitlyandwecanhandoverthatexceptionobjecttotheJVMexplicitlybythrowkeyword.Thepurposeofthrowkeywordistohandoverourcreatedexceptionobjectexplicitlytothe



JVM.Example1:classTest{publicstaticvoidmain(String[]args){System.out.println(10/0)}}InthiscaseArithmeticExceptionobjectcreatedimplicitlyandhandovertotheJVMautomaticallybythemainmethod.Example2:classTest{Publicstaticvoidmain(String[]args){ThrownewArithmeticException(/byZero)}}InthiscasecreationofanexceptionobjectandhandovertotheJVMexplicitlybytheprogrammer.

Q242.IsitpossibletothrowanError?Ans.Yes,ItispossibletothrowanyThrowabletypeincludingError.

Q243.Isitpossibletothrowanyjavaobject?Ans.No,wecanusethrowkeywordonlyforthrowableobjectsotherwisewewillgetcompiletimeerrorsayingincompatibletype.*CoreJava*Servlets&JSP*Struts*EJB*J2ME

Q244.Afterthrowisitallowtotakeanystatementdirectly?

Ans.AfterthrowstatementwearenotallowtoplaceanystatementdirectlyviolationleadstocompiletimeerrorsayingUnreachableStatement.

Q245.Whatisthepurposeofthrows?Ans.Themainpurposeofthrowskeywordistodelegatetheresponsibilitiesofexceptionhandlingtothecaller.Itrequiresinthecaseofcheckedexception.

Q246.Whatisthedifferencebetweenthrowandthrows?Ans.SometimeswecancreateExceptionobjectexplicitlyandwecanhandoverthatexceptionobjecttotheJVMexplicitlybythrowkeyword.ThemainpurposeofthrowkeywordistohandoverourcreatedexceptionobjectexplicitlytotheJVM.Themainpurposeofthrowskeywordistodelegatetheresponsibilitiesofexceptionhandlingtothecaller.Itrequiresinthecaseofcheckedexception.

Q47.Whatisthedifferencebetweenthrowandthrown?Ans.Thereisnoterminologyofthrowninjava.

Q248.Isitpossibletousethrowskeywordforanyjavaclass?Ans.No,wecanusethrowskeywordonlyforThrowableclasses.OtherwisewewillgetcompiletimeerrorsayingIncompatibletypes.



Q249.Ifwearetakingcatchblockforanexceptionbutthereisnochanceofrisingthatexceptionintrythenwhatwillhappen?

Ans. If there isnochanceof raisinganexception in try thenwearenotallow towritecatchblockforthatexceptionviolationleadstocompiletimeerror.Butthisruleisapplicableonlyforfullycheckedexception.

Q250.ExplainExceptionHandlingkeyword?Ans.ExceptionHandlingkeyword:Try:TomaintainRiskycode.Catch:TomaintainExceptionHandlingcode.Finally:Tomaintainthecleanupcode.Throw: To handover our created exception object to the JVM explicitly. Throws: TodelegatetheresponsibilitiesofExceptionHandlingtothecaller.

Q251.WhichclassactasrootforentirejavaExceptionhierarchy?Ans.ThrowableclassactasrootforentirejavaExceptionhierarchy.

Q252.WhatisthedifferencebetweenErrorandException?Ans.Throwableclasscontaintwochildclasses.Exception:Thesearemostlycausedbyourprogramandarerecoverable.

Error: These are not caused by our program, mostly caused by lake of systemresources.Thesearenonrecoverable.

Q253. What is difference between checked exception and uncheckedexception?Ans.Theexceptionswhichare checkedby the compiler for smoothexecutionofthe program at Runtime is called checked exception. Example: IOException,InterruptedException.Theexceptions which are not checked by the compiler are called unchecked exception.Example:ArithmeticException,RuntimeException.

Q254.WhatisdifferencebetweenpartiallycheckedandfullycheckedException?Ans.Acheckedexceptionissaidtobefullycheckedifandonlyifallthechildclassesalsocheckedotherwiseitiscalledpartiallycheckedexception.Example:IOException: fully checked exception Exception:partially checked exception Throwable: partiallychecked exception RuntimeException: uncheckedexception

Q255.WhatisacustomizedException?Ans.SometimesbasedonourprogrammingrequirementwehavetocreateourownexceptionsuchtypeofexceptionarecalledcustomizeException.Example:TooYoungExceptionTooOldExceptionInsufficientFundException

Q256.ExplaintheprocessofcreatingthecustomizedException.Ans.CreatingcustomizedException:ClassTooYoungExceptionextendsRuntimeException{TooYoungExcetpion(Stringdesc){Super(desc)}



}ClassTooOldExceptionextendsRuntimeException{TooOldException(Stringdesc){super(desc)}}ClasscustExcepiton{Publicstaticvoidmain(String[]args){intage=Integer.parseInt(args[0])if(age>60)

{ThrownewTooYoungException(Pleasewaitsomemoretime,definitelyyouwillgetbestmatch)}elseif(age



Ans.NullPointerException,ArrayIndexOutofBoundException,StackOverFlowError,ClassCastException,NoClassDefFoundError,ExceptionInitilizerError,IllegalArgumentException,NumberFormatException,IllegalStateException,AssertionError.

Q259.WhatisMultitasking?Ans.Executingseveraltasksimultaneouslyiscalledmultitasking.

Q260.WhatisthedifferencebetweenprocessbasedandThreadbasedMultitasking?Ans.Processbasedmultitasking:Executingseveraltasksimultaneouslywhereeachtaskisaseparate independent process such type of multitasking is called process basedMultitasking.Example:While typing a program in the editor we can listenMP3 audio songs. At thesametimewedownloada file from thenet.all these taskareexecutingsimultaneouslyandeachtaskisaseparateindependentprogram.henceitisprocessbasedmultitasking.Itisbestsuitableatoperatingsystemlevel.Threadbasedmultitasking:ExecutingseveraltasksimultaneouslywhereeachtaskisaseparateindependentpartofthesameprogramiscalledThreadbasedmultitasking.andeveryindependentpartiscalledathread.Thistypeofmultitaskingisbestsuitableatprogrammaticlevel.

Q261.WhatisMultithreadingandexplainitsapplicationareas?Ans.Executingseveralthreadsimultaneouslywhereeachthreadisaseparateindependentpartofthesameprogramiscalledmultithreading.Javalanguageprovidesinbuiltsupportformultithreadingbydefiningareachlibrary,classesandinterfaceslikeThread,ThreadGroup,Runnableetc.Themainimportantapplicationareaofmultithreadingarevideogamesimplementation,animationdevelopment,multimediagraphicsetc.

Q262.WhatisadvantageofMultithreadin

Ans.Themainadvantageofmultithreadingisreducesresponsetimeandimprovesperformanceofthesystem.

Q263.WhencomparedwithC++whatistheadvantageinjavawithrespecttoMultithreading?Ans.Javalanguageprovidesinbuiltsupportformultithreadingbydefiningareachlibrary,classesandinterfaceslikeThread,ThreadGroup,Runnableetc.Butinc++thereisnoinbuiltsupportformultithreading.

Q264.InhowmanywayswecandefineaThread?AmongextendingThreadandimplementingRunnablewhichisrecommended?Ans.WecandefineaThreadinthefollowingtwoways:1.byextendingThreadclassor2.byimplementingRunnableinterface.

AmongthetwowaysofdefiningathreadimplementingRunnablemechanismisalwaysrecommended.InthefirstapproachasourThreadclassalreadyextendingThreadthereisnochanceofextendinganyother.Hence,wemissingthekeybenefitofoops(inheritanceproperties).

Q265.Whatisthedifferencebetweent.start()andt.run()method?



Ans.Inthecaseoft.start()method,anewthreadwillbecreatedwhichisresponsiblefortheexecutionofrun()method.Butinthecaseoft.run()methodnonewthreadwillbecreatedmainthreadexecutesrun()methodjustlikeanormalmethodcall.

Q266.ExplainaboutThreadScheduler?Ans.IfmultiplethreadsarewaitingforgettingthechanceforexecutingthenwhichthreadwillgetchancefirstdecidedbyThreadScheduler.ItisthepartofJVManditsbehaviorisvendordependentandwecantexpectexactoutput.Wheneverthesituationcomestomultithreadingtheguaranteebehaviorisveryverylow.

Q267.Ifwearenotoverridingrun()methodwhatwillhappened?Ans.Ifwearenotoverridingrun()methodthenThreadclassrun()methodwillexecutedwhichhasemptyimplementationandhencewewillnotgetanyoutput.

Q268.Isoverloadingofrun()methodispossible?Ans.Yes,wecanoverloadrun()methodbutThreadclassstart()methodalwaysinvokesnoargumentrun()methodonly.Theotherrun()methodwehavetocallexplicitlythenonlywillbeexecuted.

Q269.Isitpossibletooverridestart()method?Ans.Yesitispossible.Butnotrecommended.

Q270.Ifweareoverridingstart()methodthenwhatwillhappen?Ans.Itweareoverridingstart()methodthenourownstart()methodwillbeexecutedjustlikeanormalmethodcall.InthiscasenonewThreadwillbecreated.

Q271.ExplainlifecycleofaThread?Ans.OncewecreateaThreadobjectthentheThreadissaidtobeinNew/Bornstateoncewecallt.start()methodnowtheThreadwillbeenteredintoready/RunnablestatethatisThreadisreadytoexecute.IfThreadSchedulerallocatesCPUnowtheThreadwillenteredintotheRunningstateandstartexecutionofrun()method.Aftercompletingrun()methodtheThreadenteredintoDeadState.

Q272.WhatistheimportanceofThreadclassstart()method?Ans.Start()methodpresentinThreadclassperformingalllowleveljoiningformalitiesforthenewlycreatedthreadlikeregisteringthreadwithThreadScheduleretcandthenstart()methodinvoking run() method.As the start() method is doing all low level mandatoryactivities,Programmerhas to concentrate only on run()method to define the job.Hence, start()method is a big assistant to the programmer.Without executing Thread class start()methodthereisnochanceofstartinganewThread.

Q273.AfterstartingaThreadifwetryingtorestartthesamethreadonceagainwhatwillhappen?

Ans. After starting a Thread restarting of the same Thread once again is not allowedviolationleadstoRuntimeExceptionsayingIllegalThreadStateException.

Q274.ExplainThreadclassconstructors?Ans.ThereareeightconstructorsareavailableinThreadclass:



1.Threadt=newThread()2.Threadt=newThread(Runnabler)3.Threadt=newThread(Stringname)4.Threadt=newThread(Runnabler,Stringname)5.Threadt=newThread(ThreadGroupg,Stringname)6.Threadt=newThread(ThreadGroupg,Runnabler)

7.Threadt=newThread(ThreadGroupg,Runnabler,Stringname)8.Threadt=newThread(ThreadGroupg,Runnabler,Stringname,longstacksize)

Q275.HowtogetandsetnameofaThread?Ans.ForeveryThreadinjavathereisaname.TosetandgetthenameofaThreadwecanusethefollowingmethods.Allmethodsarefinal.1.PublicfinalvoidsetName(Stringname)TosetthenameofaThread2.PublicfinalStringgetName()TogetthenameofaThread.

Q276.WhatistherangeofThreadpriorityinjava?Ans.ThevalidrangeofaThreadpriorityis110.(1isleastpriorityand10ishighestpriority)

Q277.WhousesThreadpriority?Ans.ThreadSchedulerusesprioritieswhileallocatingCPU.TheThreadwhichishavinghighestprioritywillgetchancefirstforexecution.

Q278.WhatisthedefaultpriorityoftheThread?Ans.Thedefaultpriorityonlyforthemainthreadis5butforallremainingthreadsdefaultprioritywillbeinheritingfromparenttochild.Whateverpriorityparentthreadhasthesamewillbeinheritedtothechildthread.

Q279.OncewecreatedanewThreadwhataboutitspriority?Ans.Whateverpriorityparentthreadhasthesamewillbeinheritedtothenewchildthread.

Q280.HowtogetandsetpriorityofaThread?Ans.TogetandsetpriorityofaThread,Threadclassdefinesthefollowingtwomethods:1. Public final intgetPriority()2.PublicfinalvoidsetPriority(intpriority)

Q281.IfwearetryingtosetpriorityofaThreadas100whatwillhappen?Ans.IfwearetryingtosetpriorityofaThreadas100thenwewillnotgetanycompiletimeerrorbutattheruntimewewillgetRuntimeexceptionIllegalArgumentException.BecausethevalidrangeoftheThreadpriorityis(110)only.

Q282.Iftwothreadshavingsameprioritythenwhichthreadwillgetchancefirstforexecution?Ans.IftwothreadshavingsameprioritythenwhichthreadwillgetthechancefirstforexecutiondecidedbyThreadScheduler.Itisthepartof

JVManditsbehaviorisvendordependentandwecantexpectexactoutput.

Q283.Iftwothreadshavingdifferentprioritythenwhichthreadwillgetchancefirstforexecution?Ans.IftwothreadshavingdifferentprioritythentheThreadwhichishavinghighestprioritywillgetchancefirstforexecution.



Q284.Howwecanpreventathreadfromexecution?Ans.WecanpreventaThreadfromexecutinbyusingthefollowingmethods:1.Yield()2.Join()3.Sleep()

Q285.Whatisyield()method?Explainitspurpose?Ans.yield()methodcausesthecurrentexecutingthreadtopauseexecutionandgivethechanceforwaitingthreadaresamepriority.Ifthereisnowaitingthreadoralltheremainingwaitingthreadhavelowprioritythenthesamethreadwillgetchanceonceagainforexecution.TheThreadwhichisyieldedwhenitwillgetchanceonceagainforexecutiondependsuponmercyofThreadscheduler.Publicstaticnativevoidyield()

Q286.Whatispurposeofjoin()method?Ans.IfaThreadwantstowaituntilsomeotherThreadcompletionthenweshouldgoforjoin()method.Example:ifaThreadt1executet2.join()thent1willenteredintowaitingstateuntilt2Threadcompletion.

Q287.Isjoin()methodisoverloaded?Ans.Yesjoin()methodisoverloadedmethod.Publicfinalvoidjoin()throwsInterruptedExceptionByusingthismethodthreadwillwaituptoanotherthreadcompletion.Publicfinalvoidjoin(longms)throwsInterruptedExceptionByusingthismethodthreadwillwailuptosometimewhatwearepassingasaargumentinmillisecondPublic final void join(long ms, int ns)throws InterruptedException By using thismethod threadwill wait up to sometimewhat we are passing as a argument inmillisecondandnanosecond.

Q288.Whatisthepurposeofsleep()method?Ans.IfaThreaddontwanttoperformanyoperationforaparticularamountoftimethenweshouldgoforsleep()method.Wheneverweare

usingsleep()methodcompulsoryweshouldhandleInterruptedExceptioneitherbyusingtrycatchorbyusingthrowskeywordotherwisewewillgetcompiletimeerror.

Q289.Whatissynchronizedkeyword?Explainitsadvantagesanddisadvantages.Ans.Synchronizedkeywordisapplicableformethodandblocksonly.Wecantuseforvariablesandclasses.IfamethoddeclaredasasynchronizedthenatatimeonlyoneThreadisallowtoexecutethatmethodonthegivenobject.Themainadvantagesofsynchronizedkeywordare,wecanpreventdatainconsistencyproblemsandwecanprovideThreadsafty.ButthemainlimitationofsynchronizedkeywordisitincreaseswaitingtimeofThreadsandeffectperformanceofthesystem.Henceifthereisnospecificrequirementitisnotrecommendedtousesynchronizedkeyword.

Q290.Wherewecanusesynchronizedkeyword?Ans.SynchronizationconceptisapplicablewhenevermultipleThreadsareoperatingonthe



sameobjectsimultaneously.ButwhenevermultipleThreadsareoperatingondifferentobjectsthenthereisnoimpactofsynchronization.

Q291.Whatisobjectlock?Explainwhenitisrequired?Ans.Everyobjectinjavahasauniquelockwheneverweareusingsynchronizationconceptthenonlylockconceptwillcomingtothepicture.IfaThreadwantstoexecuteasynchronizedmethodfirstithastogetthelockoftheobject.OnceaThreadgotthelockthenitisallowtoexecuteanysynchronizedmethodonthatobject.AftercompletingsynchronizedmethodexecutionThreadreleasesthelockautomatically.WhileaThreadexecutingsynchronizedmethodonthegivenobjecttheremainingThreadsarenotallowtoexecuteanysynchronizedmethodonthatobjectsimultaneously.ButremainingThreadsareallowtoexecuteanynonsynchronizedmethodsimultaneously.(Lockconceptisimplementedbasedonobjectbutnotbasedonmethod.)

Q292.Whatistheclasslevellock?Explainitspurpose.Ans.EveryclassinjavahasauniquelockifaThreadwantstoexecutestaticsynchronizedmethodthatThreadhastogetclasslevellockonceaThreadgotclasslevellockthenonlyitisallowtoexecutestaticsynchronizedmethod.WhileaThreadexecutinganystaticsynchronizedmethodthenremainingThreadsarenotallowtoexecuteanystaticsynchronizedmethodofthesameclasssimultaneously.ButtheremainingThreadsareallowtoexecutethefollowingmethodsimultaneously:

1.Anystaticnonsynchronizedmethod.2.Synchronizedinstancemethods3.Nonsynchronizedinstancemethod.Thereisnorelationshipbetweenobjectlockandclasslevellock,bothareindependent.

Q293.Whileathreadexecutinganysynchronizedmethodonthegivenobjectisitpossibletoexecuteremainingsynchronizedmethodofthesameobjectsimultaneouslybyanyotherthread?Ans.No,itisnopossible.

Q294.Whatisthedifferencebetweensynchronizedmethodandstaticsynchronizedmethod?Ans.IfaThreadwantstoexecuteasynchronizedmethodfirstithastogetthelockoftheobject.OnceaThreadgotthelockthenitisallowtoexecuteanysynchronizedmethodonthatobject.IfaThreadwantstoexecutestaticsynchronizedmethodthatThreadhastogetclasslevellockonceaThreadgotclasslevellockthenonlyitisallowtoexecutestaticsynchronizedmethod.

Q295.Whatistheadvantageofsynchronizedblockoversynchronizedmethod?Ans.Ifveryfewlinesofthecoderequiredsynchronizationthendeclaringentiremethodasthesynchronizedisnotrecommended.Wehavetodeclarethosefewlinesofthecodeinsidesynchronizedblock.ThisapproachreduceswaitingtimeoftheThreadandimprovesperformanceofthesystem.

Q296.Whatissynchronizedstatement?Ans.TheStatementwhichisinsidethesynchronizedarea(synchronizedmethodorsynchronizedblock)iscalledsynchronizedstatement.



Q297.Howwecandeclaresynchronizedblocktogetclasslevellock?Ans.Togettheclasslevellockwecandeclaresynchronizedblockasfollows:synchronized(Display.class){}

Q298.Howtwothreadwillcommunicatewitheachother?Ans.TwoThreadswillcommunicatewitheachotherbyusingwait(),notify(),notifyAll()methods.

Q299.wait(),notify(),notifyAll()methodcanavailableinwhich

class?Ans.ThesemethodsaredefinedinObjectclass.

Q300.Whywait(),notify(),notifyAll()methoddefinesinobjectclassinsteadofThreadclass?Ans.ThesemethodsaredefinedinObjectclassbutnotinThreadbecauseThreadsarecallingthismethodonthesharedobject.

Q301.Ifawaitingthreadgotnotificationthenitwillenteredintowhichstate?Ans.Itwillenteredintoanotherwaitingstatetogetlock.

Q302.Inwhichmethodthreadscanreleasethelock?Ans.OnceaThreadcallswait()method it immediately releases the lockof thatobjectandthenenteredintowaitingstatesimilarlyaftercallingnotify()methodThreadreleasesthelockbutmaynotimmediately.Exceptthesethreemethods(wait(),notify(),notifyAll())methodThreadneverreleasesthelockanywhereelse.

Q303.Explainwait(),notify(),notifyAll()methoduses.Ans.TwoThreadswillcommunicatewitheachotherbyusingwait(),notify()ornotifyAll()methods.ThesemethodsaredefinedinObjectclassbutnotinThreadbecauseThreadsarecallingthismethod.

Q304.Whatisthedifferencebetweennotify()andnotifyAll()?Ans.Togivenotification to thesinglewaitingThread.Weusenotify()methodand togivenotificationtoallwaitingthreadweusenotifyAll()method.

Q305.OnceaThreadgotthenotificationthenwhichwaitingthreadwillgetchance?Ans.ItisdependsontheThreadScheduler.

Q306.Howathreadcaninterruptanotherthread?Ans.AThreadcaninterruptanotherThreadbyusinginterrupt()method.

Q307.WhichkeywordcausesDeadLocksituation?Ans.SynchronizedkeywordisthethingtocausesofDeadLock.IfwearenotusingproperlysynchronizedkeywordtheprogramwillenteredintoDeadLocksituation.

Q308.Howwecanstopathreadexplacitly?Ans.Threadclassdefinesstop()methodbyusingthismethodwecanstopaThread.Butitisdeprecated.Andhencenotrecommendedtouse.



Q309.Explainaboutsuspend()andresume()method?Ans.AThreadcansuspendanotherThreadbyusingsuspend()method.AThreadcanresumeasuspendedThreadbyusingresume()method.

Q310.WhatisStarvation()?AndExplainthedifferencebetweenDeadlockandStarvation?Ans.AlongwaitingThreadissaidtobeinstarvation(becauseofleastpriority)butaftercertaintimedefiantlyitwillgetthechanceforexecution.ButinthecaseofDeadlocktwoThreadswillwaitforeachotherforever.Itwillnevergetthechanceforexecution.

Q311.Whatisracecondition?Ans.MultipleThreadsareaccessingsimultaneouslyandcausingdata inconsistencyproblemiscalledracecondition,wecanresolvethisbyusingsynchronizedkeyword.

Q312.WhatisDaemonThread?Andgiveanexample?Ans.TheThreadswhicharerunninginthebackgroundarecalledDaemonThread.Example:Garbagecollector.

Q313.WhatisthepurposeofaDaemonThread?Ans.ThemainpurposeofDaemonThreadsistoprovidesupportfornondaemonThreads.

Q314.HowwecancheckDaemonnatureofaThread?Ans.WecancheckDaemonnatureofaThreadbyusingisDaemon()method.

Q315.IsitpossibletochangeaDaemonnatureofaThread?Ans.Yes,wecanchangeDaemonnatureofaThreadbyusingsetDaemon()method.

Q316.IsmainthreadisDaemonornondaemon?Ans.Bydefaultmainthreadisalwaysnondaemonnature.

Q317.Oncewecreatedanewthreadisitdaemonornondaemon.Ans.OncewecreatedanewThread,TheDaemonnaturewillbeinheritingfromparenttochild.IftheparentisDaemonthechildisalsoDaemonandiftheparentisnondaemonthenchildisalsonondaemon

[https://www.blogger.com/null]

Q318.AfterstartingathreadisitpossibletochangeDaemonnature?Ans.WecanchangetheDaemonnaturebeforestartingtheThreadonly.OnceThreadstartedwearenotallowtochangeDaemonnatureotherwisewewillgetRuntimeExceptionsyingIllegalThreadStateException.

Q319.WhentheDaemonthreadwillbeterminated?Ans.OncelastnondaemonThreadterminatesautomaticallyeveryDaemonThreadwillbeterminated.

Q320.WhatisgreenThread?Ans.AgreenthreadreferstoamodeofoperationfortheJavaVirtualMachine(JVM)inwhichallcodeisexecutedinasingleoperatingsystemthread.IftheJavaprogramhas



anyconcurrentthreads,theJVMmanagesmultithreadinginternallyratherthanusingotheroperatingsystemthreads.ThereisasignificantprocessingoverheadfortheJVMtokeeptrackofthreadstatesandswap between them, so green threadmode has been deprecated and removed frommorerecentJavaimplementations.

Q321.ExplainaboutThreadgroup?Ans.EveryJavathreadisamemberofathreadgroup.Threadgroupsprovideamechanismforcollectingmultiplethreadsintoasingleobjectandmanipulatingthosethreadsallatonce,ratherthanindividually.Forexample,youcanstartorsuspendallthethreadswithinagroupwithasinglemethodcall.JavathreadgroupsareimplementedbytheThreadGroupapiclassinthejava.langpackage.

Q322.WhatistheThreadLocal?Ans.It'sawayforeachthreadinmultithreadedcodetokeepitsowncopyofaninstancevariable.Generally,instancevariablearesharedbetweenallthreadsthatuseanobjectThreadLocalisawayforeachthreadtokeepitsowncopyofsuchavariable.Thepurposemightbethateachthreadkeepsdifferentdatainthatvariable,orthatthedeveloperwantstoavoidtheoverheadofsynchronizingaccesstoit.

Q323.Whatisinnerclassandwhenweshouldgoforinnerclasses?SometimeswecandeclareaclassinsideanotherclasssuchtypeofclassesarecalledinnerclassesExampleClassCar{

//morecodehereClassEngine{//morecodehere}}WithoutexistingCarobjectthereisnochanceofexistingEngineobject,henceEngineclasshasdeclaredinsideCarclass.

Q324.Howmanytypesofinnerclassesarepresent?TherearefourtypesofinnerclassesarepresentoNormalorregularinnerclassoMethodlocalinnerclassoAnonymousinnerclassoStaticnestedclass

Q325.Whatismethodlocalinnerclass?SometimeswecandeclareaclassinsideamethodsuchtypeofclassesarecalledmethodlocalinnerclassesThemainpurposeofmethodlocalinnerclassesistodefinemethodspecificfunctionalityThescopeofmethodlocalinnerclassesisthescopeofthemethodwhereitisdeclared.Thisisthemostlyrarelyusedtypeofinnerclasses.ExampleclassTest{publicvoidm1(){classInner{publicvoidsum(intI,intj){



System.out.println(i+J)}//sum}//innerInneri=newInner()i.sum(10,20)//morecodehereI.sum(100,303)//morecodeherei.sum(102,84)}//m1()Publicstaticvoidmain(){NewTest().m1()}}

Q326.Whatisanonymousinnerclass?SometimeswecandeclareainnerclasswithoutnamesuchtypeofinnerclassesarecalledAnonymousinnerclassesAnonymousinnerclassescanbedividedinto3categoriesAnonymousinnerclassthatextendsaclass

AnonymousinnerclassthatimplementsaninterfaceAnonymousinnerclassthatdefinesinsideamethodargumentANONYMOUSINNERCLASSTHATEXTENDSACLASSExampleClasspopcorn{Publicvoidtaste(){System.out.println(itissalty)}//morecodehere}ClassTest{Publicstaticvoidmain(String[]args){Popcornp=newPopcorn(){//herewearecreatingchildclassforpopcornPublicvoidtaste(){System.out.println(itissweet)}}//heresemicolonindicateswercreatingchildclassobjectwithparent//classreferenceherechildclassdosentcontainnamep.taste()//itissweetPopcornp=newPopcorn()p1.taste()//itissalty}}

ANONYMOUSINNERCLASSTHATIMPLEMENTSANINTERFACEexampleclassTest{Publicstaticvoidmain(String[]args){Runnabler=newRunnable(){Publicvoidrun(){for(inti=0i



Q327.Whatisstaticnestedcalss?whythetermnestedinsteadofinnerinstaticnestedclass?

Sometimeswecandeclareinnerclasswithstaticmodifiersuchtypeofinnerclassarecalledstaticnestedclasses.thetermnestedinsteadofstaticbecausewithoutexistingouterclassobjectinnerclassobjectcanexist.ExampleClassouter{StaticclassNested{Publicstaticvoidmain(String[]args){System.out.println(nestedclassmain())}}Publicstaticvoidmain(String[]args){System.out.println(outerclassmain())}}JavaOuterO/POuterclassmain()JavaOuter$NestedO/PNestedclassmain()

Q328.Insideinnerclassisitpossibletodeclaremain()?Noitisnotpossibletodeclaremain()insideinnerclassbutinstaticnestedclassitispossibleforExamplereferaboveco

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