java英文面试笔试题

java英文面试笔试题

Question:Whatistransientvariable?

Answer:Transientvariablecantbeserialize.ForexampleifavariableisdeclaredastransientinaSerializableclassandtheclassiswrittentoanObjectStream,thevalueofthevariablecantbewrittentothestreaminsteadwhentheclassisretrievedfromtheObjectStreamthevalueofthevariablebecomesnull.

Question:NamethecontainerswhichusesBorderLayoutastheirdefaultlayout?

Answer:ContainerswhichusesBorderLayoutastheirdefaultare:window,FrameandDialogclasses.

Question:WhatdoyouunderstandbySynchronization?

Answer:Synchronizationisaprocessofcontrollingtheaccessofsharedresourcesbythemultiplethreadsinsuchamannerthatonlyonethreadcanaccessoneresourceatatime.Innonsynchronizedmultithreadedapplication,itispossibleforonethreadtomodifyasharedobjectwhileanotherthreadisintheprocessofusingorupdatingtheobjectsvalue.Synchronizationpreventssuchtypeofdatacorruption.

E.g.Synchronizingafunction:

publicsynchronizedvoidMethod1(){

//Appropriatemethod-relatedcode.

}

E.g.Synchronizingablockofcodeinsideafunction:

publicmyFunction(){

synchronized(this){

//Synchronizedcodehere.

}

}

Question:WhatisCollectionAPI?

Answer:TheCollectionAPIisasetofclassesandinterfacesthatsupportoperationoncollectionsofobjects.Theseclassesandinterfacesaremoreflexible,morepowerful,andmoreregularthanthevectors,arrays,andhashtablesifeffectivelyreplaces.

Exampleofclasses:HashSet,HashMap,ArrayList,LinkedList,TreeSetandTreeMap.

Exampleofinterfaces:Collection,Set,ListandMap.

Question:IsIteratoraClassorInterface?Whatisitsuse?

Answer:IteratorisaninterfacewhichisusedtostepthroughtheelementsofaCollection.

Question:Whatissimilarities/differencebetweenanAbstractclassandInterface?

Answer:Differencesareasfollows:

Interfacesprovideaformofmultipleinheritance.Aclasscanextendonlyoneotherclass.

Interfacesarelimitedtopublicmethodsandconstantswithnoimplementation.Abstractclassescanhaveapartialimplementation,protectedparts,staticmethods,etc.

AClassmayimplementseveralinterfaces.Butincaseofabstractclass,aclassmayextendonlyoneabstractclass.

Interfacesareslowasitrequiresextraindirectiontotofindcorrespondingmethodinintheactualclass.Abstractclassesarefast.

Similarities:

NeitherAbstractclassesorInterfacecanbeinstantiated.

Question:HowtodefineanAbstractclass?

Answer:AclasscontainingabstractmethodiscalledAbstractclass.AnAbstractclasscantbeinstantiated.

ExampleofAbstractclass:

abstractclasstestAbstractClass{

protectedStringmyString;

publicStringgetMyString(){

returnmyString;

}

publicabstractstringanyAbstractFunction();

}

Question:HowtodefineanInterface?

Answer:InJavaInterfacedefinesthemethodsbutdoesnotimplementthem.Interfacecanincludeconstants.AclassthatimplementstheinterfacesisboundtoimplementallthemethodsdefinedinInterface.

EmapleofInterface:

publicinterfacesampleInterface{

publicvoidfunctionOne();

publiclongCONSTANT_ONE=1000;

}

Question:ExplaintheuserdefinedExceptions?

Answer:UserdefinedExceptionsaretheseparateExceptionclassesdefinedbytheuserforspecificpurposed.Anuserdefinedcancreatedbysimplysub-classingittotheExceptionclass.Thisallowscustomexceptionstobegenerated(usingthrow)andcaughtinthesamewayasnormalexceptions.

Example:

classmyCustomExceptionextendsException{

//Theclasssimplyhastoexisttobeanexception

}

Question:ExplainthenewFeaturesofJDBC2.0CoreAPI?

Answer:TheJDBC2.0APIincludesthecompleteJDBCAPI,whichincludesbothcoreandOptionalPackageAPI,andprovidesinductrial-strengthdatabasecomputingcapabilities.

NewFeaturesinJDBC2.0CoreAPI:

Scrollableresultsets-usingnewmethodsintheResultSetinterfaceallowsprogrammaticallymovethetoparticularrowortoapositionrelativetoitscurrentposition

JDBC2.0CoreAPIprovidestheBatchUpdatesfunctionalitytothejavaapplications.

JavaapplicationscannowusetheResultSet.updateXXXmethods.

Newdatatypes-interfacesmappingtheSQL3datatypes

Custommappingofuser-definedtypes(UTDs)

Miscellaneousfeatures,includingperformancehints,theuseofcharacterstreams,fullprecisionforjava.math.BigDecimalvalues,additionalsecurity,andsupportfortimezonesindate,time,andtimestampvalues.

Question:Explaingarbagecollection?

Answer:GarbagecollectionisoneofthemostimportantfeatureofJava.GarbagecollectionisalsocalledautomaticmemorymanagementasJVMautomaticallyremovestheunusedvariables/objects(valueisnull)fromthememory.Userprogramcanntdirectlyfreetheobjectfrommemory,insteaditisthejobofthegarbagecollectortoautomaticallyfreetheobjectsthatarenolongerreferencedbyaprogram.Everyclassinheritsfinalize()methodfromjava.lang.Object,thefinalize()methodiscalledbygarbagecollectorwhenitdeterminesnomorereferencestotheobjectexists.InJava,itisgoodideatoexplicitlyassignnullintoavariablewhennomoreinuse.IJavaoncallingSystem.gc()andRuntime.gc(),JVMtriestorecycletheunusedobjects,butthereisnoguaranteewhenalltheobjectswillgarbagecollected.

Question:Howyoucanforcethegarbagecollection?

Answer:Garbagecollectionautomaticprocessandcantbeforced.

Question:WhatisOOPS?

Answer:OOPisthecommonabbreviationforObject-OrientedProgramming.

Question:DescribetheprinciplesofOOPS.

Answer:TherearethreemainprincipalsofoopswhicharecalledPolymorphism,InheritanceandEncapsulation.

Question:ExplaintheEncapsulationprinciple.

Answer:Encapsulationisaprocessofbindingorwrappingthedataandthecodesthatoperatesonthedataintoasingleentity.Thiskeepsthedatasafefromoutsideinterfaceandmisuse.