Master list of Java interview questions115 questions.docx
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Master list of Java interview questions115 questions.docx
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MasterlistofJavainterviewquestions115questions
1.Whatisthedifferencebetweenproceduralandobject-orientedprograms?
-a)Inproceduralprogram,programminglogicfollowscertainproceduresandtheinstructionsareexecutedoneafteranother.InOOPprogram,unitofprogramisobject,whichisnothingbutcombinationofdataandcode.b)Inproceduralprogram,dataisexposedtothewholeprogramwhereasinOOPsprogram,itisaccessiblewithintheobjectandwhichinturnassuresthesecurityofthecode.
2.WhatareEncapsulation,InheritanceandPolymorphism?
-Encapsulationisthemechanismthatbindstogethercodeanddataitmanipulatesandkeepsbothsafefromoutsideinterferenceandmisuse.Inheritanceistheprocessbywhichoneobjectacquiresthepropertiesofanotherobject.Polymorphismisthefeaturethatallowsoneinterfacetobeusedforgeneralclassactions.
3.WhatisthedifferencebetweenAssignmentandInitialization?
-Assignmentcanbedoneasmanytimesasdesiredwhereasinitializationcanbedoneonlyonce.
4.WhatisOOPs?
-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
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