Java英文面试题经典.docx

Java英文面试题经典.docx

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Java英文面试题经典

Java-英文面试题-经典

英文Java面试题

Question:

Whatistransientvariable?

Answer:

Transientvariablecan'tbeserialize.ForexampleifavariableisdeclaredastransientinaSerializableclassandtheclassiswrittentoanObjectStream,thevalueofthevariablecan'tbewrittentothestreaminsteadwhentheclassisretrievedfromtheObjectStreamthevalueofthevariablebecomesnull.

Question:

NamethecontainerswhichusesBorderLayoutastheirdefaultlayout?

Answer:

ContainerswhichusesBorderLayoutastheirdefaultare:

window,FrameandDialogclasses.

Question:

WhatdoyouunderstandbySynchronization?

Answer:

Synchronizationisaprocessofcontrollingtheaccessofsharedresources

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.

Interfacesareslowasitrequiresextraindirectiontofindcorrespondingmethodintheactualclass.Abstractclassesarefast.

Similarities:

NeitherAbstractclassesorInterfacecanbeinstantiated.

Question:

HowtodefineanAbstractclass?

Answer:

AclasscontainingabstractmethodiscalledAbstractclass.AnAbstractclasscan'tbeinstantiated.

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.Userprogramcann'tdirectlyfreetheobjectfrommemory,insteaditisthejobofthegarbagecollectortoautomaticallyfreetheobjectsthatarenolongerreferencedbyaprogram.Everyclassinheritsfinalize（）methodfromjava.lang.Object,thefinalize（）methodiscalledbygarbagecollectorwhenitdeterminesnomorereferencestotheobjectexists.InJava,itisgoodideatoexplicitlyassignnullintoavariablewhennomoreinuse.IJavaoncallingSystem.gc（）andRuntime.gc（）,JVMtriestorecycletheunusedobjects,butthereisnoguaranteewhenalltheobjectswillgarbagecollected.