Master list of Java interview questions115 questionsWord下载.docx

Master list of Java interview questions115 questionsWord下载.docx

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-Objectorientedprogrammingorganizesaprogramarounditsdata,i.e.,objectsandasetofwelldefinedinterfacestothatdata.Anobject-orientedprogramcanbecharacterizedasdatacontrollingaccesstocode.

5.WhatareClass,ConstructorandPrimitivedatatypes?

-Classisatemplateformultipleobjectswithsimilarfeaturesanditisablueprintforobjects.Itdefinesatypeofobjectaccordingtothedatatheobjectcanholdandtheoperationstheobjectcanperform.Constructorisaspecialkindofmethodthatdetermineshowanobjectisinitializedwhencreated.Primitivedatatypesare8typesandtheyare:

byte,short,int,long,float,double,boolean,char.

6.WhatisanObjectandhowdoyouallocatememorytoit?

-Objectisaninstanceofaclassanditisasoftwareunitthatcombinesastructuredsetofdatawithasetofoperationsforinspectingandmanipulatingthatdata.Whenanobjectiscreatedusingnewoperator,memoryisallocatedtoit.

7.Whatisthedifferencebetweenconstructorandmethod?

-Constructorwillbeautomaticallyinvokedwhenanobjectiscreatedwhereasmethodhastobecalledexplicitly.

8.Whataremethodsandhowaretheydefined?

-Methodsarefunctionsthatoperateoninstancesofclassesinwhichtheyaredefined.Objectscancommunicatewitheachotherusingmethodsandcancallmethodsinotherclasses.Methoddefinitionhasfourparts.Theyarenameofthemethod,typeofobjectorprimitivetypethemethodreturns,alistofparametersandthebodyofthemethod.Amethod’ssignatureisacombinationofthefirstthreepartsmentionedabove.

9.WhatistheuseofbinandlibinJDK?

-Bincontainsalltoolssuchasjavac,appletviewer,awttool,etc.,whereaslibcontainsAPIandallpackages.

10.Whatiscasting?

-Castingisusedtoconvertthevalueofonetypetoanother.

11.Howmanywayscananargumentbepassedtoasubroutineandexplainthem?

-Anargumentcanbepassedintwoways.Theyarepassingbyvalueandpassingbyreference.Passingbyvalue:

Thismethodcopiesthevalueofanargumentintotheformalparameterofthesubroutine.Passingbyreference:

Inthismethod,areferencetoanargument（notthevalueoftheargument）ispassedtotheparameter.

12.Whatisthedifferencebetweenanargumentandaparameter?

-Whiledefiningmethod,variablespassedinthemethodarecalledparameters.Whileusingthosemethods,valuespassedtothosevariablesarecalledarguments.

13.Whataredifferenttypesofaccessmodifiers?

-public:

Anythingdeclaredaspubliccanbeaccessedfromanywhere.private:

Anythingdeclaredasprivatecan’tbeseenoutsideofitsclass.protected:

Anythingdeclaredasprotectedcanbeaccessedbyclassesinthesamepackageandsubclassesintheotherpackages.defaultmodifier:

Canbeaccessedonlytoclassesinthesamepackage.

14.Whatisfinal,finalize（）andfinally?

-final:

finalkeywordcanbeusedforclass,methodandvariables.Afinalclasscannotbesubclassedanditpreventsotherprogrammersfromsubclassingasecureclasstoinvokeinsecuremethods.Afinalmethodcan’tbeoverridden.Afinalvariablecan’tchangefromitsinitializedvalue.finalize（）:

finalize（）methodisusedjustbeforeanobjectisdestroyedandcanbecalledjustpriortogarbagecollection.finally:

finally,akeywordusedinexceptionhandling,createsablockofcodethatwillbeexecutedafteratry/catchblockhascompletedandbeforethecodefollowingthetry/catchblock.Thefinallyblockwillexecutewhetherornotanexceptionisthrown.Forexample,ifamethodopensafileuponexit,thenyouwillnotwantthecodethatclosesthefiletobebypassedbytheexception-handlingmechanism.Thisfinallykeywordisdesignedtoaddressthiscontingency.

15.WhatisUNICODE?

-Unicodeisusedforinternalrepresentationofcharactersandstringsandituses16bitstorepresenteachother.

16.WhatisGarbageCollectionandhowtocallitexplicitly?

-Whenanobjectisnolongerreferredtobyanyvariable,javaautomaticallyreclaimsmemoryusedbythatobject.Thisisknownasgarbagecollection.System.gc（）methodmaybeusedtocallitexplicitly.

17.Whatisfinalize（）method?

-finalize（）methodisusedjustbeforeanobjectisdestroyedandcanbecalledjustpriortogarbagecollection.

18.WhatareTransientandVolatileModifiers?

-Transient:

Thetransientmodifierappliestovariablesonlyanditisnotstoredaspartofitsobject’sPersistentstate.Transientvariablesarenotserialized.Volatile:

Volatilemodifierappliestovariablesonlyandittellsthecompilerthatthevariablemodifiedbyvolatilecanbechangedunexpectedlybyotherpartsoftheprogram.

19.Whatismethodoverloadingandmethodoverriding?

-Methodoverloading:

Whenamethodinaclasshavingthesamemethodnamewithdifferentargumentsissaidtobemethodoverloading.Methodoverriding:

Whenamethodinaclasshavingthesamemethodnamewithsameargumentsissaidtobemethodoverriding.

20.Whatisdifferencebetweenoverloadingandoverriding?

-a）Inoverloading,thereisarelationshipbetweenmethodsavailableinthesameclasswhereasinoverriding,thereisrelationshipbetweenasuperclassmethodandsubclassmethod.b）Overloadingdoesnotblockinheritancefromthesuperclasswhereasoverridingblocksinheritancefromthesuperclass.c）Inoverloading,separatemethodssharethesamenamewhereasinoverriding,subclassmethodreplacesthesuperclass.d）Overloadingmusthavedifferentmethodsignatureswhereasoverridingmusthavesamesignature.

21.WhatismeantbyInheritanceandwhatareitsadvantages?

-Inheritanceistheprocessofinheritingallthefeaturesfromaclass.Theadvantagesofinheritancearereusabilityofcodeandaccessibilityofvariablesandmethodsofthesuperclassbysubclasses.

22.Whatisthedifferencebetweenthis（）andsuper（）?

-this（）canbeusedtoinvokeaconstructorofthesameclasswhereassuper（）canbeusedtoinvokeasuperclassconstructor.

23.Whatisthedifferencebetweensuperclassandsubclass?

-Asuperclassisaclassthatisinheritedwhereassubclassisaclassthatdoestheinheriting.

24.Whatmodifiersmaybeusedwithtop-levelclass?

-public,abstractandfinalcanbeusedfortop-levelclass.

25.Whatareinnerclassandanonymousclass?

-Innerclass:

classesdefinedinotherclasses,includingthosedefinedinmethodsarecalledinnerclasses.Aninnerclasscanhaveanyaccessibilityincludingprivate.Anonymousclass:

Anonymousclassisaclassdefinedinsideamethodwithoutanameandisinstantiatedanddeclaredinthesameplaceandcannothaveexplicitconstructors.

26.Whatisapackage?

-Apackageisacollectionofclassesandinterfacesthatprovidesahigh-levellayerofaccessprotectionandnamespacemanagement.

27.Whatisareflectionpackage?

-java.lang.reflectpackagehastheabilitytoanalyzeitselfinruntime.

28.Whatisinterfaceanditsuse?

-Interfaceissimilartoaclasswhichmaycontainmethod’ssignatureonlybutnotbodiesanditisaformalsetofmethodandconstantdeclarationsthatmustbedefinedbytheclassthatimplementsit.Interfacesareusefulfor:

a）Declaringmethodsthatoneormoreclassesareexpectedtoimplementb）Capturingsimilaritiesbetweenunrelatedclasseswithoutforcingaclassrelationship.c）Determininganobject’sprogramminginterfacewithoutrevealingtheactualbodyoftheclass.

29.Whatisanabstractclass?

-Anabstractclassisaclassdesignedwithimplementationgapsforsubclassestofillinandisdeliberatelyincomplete.

30.WhatisthedifferencebetweenIntegerandint?

-a）Integerisaclassdefinedinthejava.langpackage,whereasintisaprimitivedatatypedefinedintheJavalanguageitself.Javadoesnotautomaticallyconvertfromonetotheother.b）Integercanbeusedasanargumentforamethodthatrequiresanobject,whereasintcanbeusedforcalculations.

31.Whatisacloneableinterfaceandhowmanymethodsdoesitcontain?

-ItisnothavinganymethodbecauseitisaTAGGEDorMARKERinterface.

32.Whatisthedifferencebetweenabstractclassandinterface?

-a）Allthemethodsdeclaredinsideaninterfaceareabstractwhereasabstractclassmusthaveatleastoneabstractmethodandothersmaybeconcreteorabstract.b）Inabstractclass,keywordabstractmustbeusedforthemethodswhereasinterfaceweneednotusethatkeywordforthemethods.c）Abstractclassmusthavesubclasseswhereasinterfacecan’thavesubclasses.

33.Canyouhaveaninnerclassinsideamethodandwhatvariablescanyouaccess?

-Yes,wecanhaveaninnerclassinsideamethodandfinalvariablescanbeaccessed.

34.Whatisthedifferenceb