Java英文面试题经典.docx
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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:
Synchronizationisaprocessofcontrollingtheaccessofsharedresourcesbythemultiplethreadsinsuchamannerthatonlyonethreadcanaccessoneresourceatatime.Innonsynchronizedmultithreadedapplication,itispossibleforonethreadtomodifyasharedobjectwhileanotherthreadisintheprocessofusingorupdatingtheobject'svalue.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.
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)
Question:
Explaingarbagecollection?
Question:
Howyoucanforcethegarbagecollection?
Answer:
Garbagecollectionautomaticprocessandcan'tbeforced.
Question:
WhatisOOPS?
Answer:
OOPisthecommonabbreviationforObject-OrientedProgramming.
Question:
DescribetheprinciplesofOOPS.
Answer:
TherearethreemainprincipalsofoopswhicharecalledPolymorphism,InheritanceandEncapsulation.
Question:
ExplaintheEncapsulationprinciple.
Answer:
Encapsulationisaprocessofbindingorwrappingthedataandthecodesthatoperatesonthedataintoasingleentity.Thiskeepsthedatasafefromoutsideinterfaceandmisuse.Onewaytothinkaboutencapsulationisasaprotectivewrapperthatpreventscodeanddatafrombeingarbitrarilyaccessedbyothercodedefinedoutsidethewrapper.
Question:
ExplaintheInheritanceprinciple.
Answer:
Inheritanceistheprocessbywhichoneobjectacquiresthepropertiesofanotherobject.
Question:
ExplainthePolymorphismprinciple.
Answer:
ThemeaningofPolymorphismissomethinglikeonenamemanyforms.Polymorphismenablesoneentitytobeusedasasgeneralcategoryfordifferenttypesofactions.Thespecificactionisdeterminedbytheexactnatureofthesituation.Theconceptofpolymorphismcanbeexplainedas"oneinterface,multiplemethods".
Question:
ExplainthedifferentformsofPolymorphism.
Answer:
Fromapracticalprogrammingviewpoint,polymorphismexistsinthreedistinctformsinJava:
Methodoverloading
Methodoverridingthroughinheritance
MethodoverridingthroughtheJavainterface
Question:
WhatareAccessSpecifiersavailableinJava?
Answer:
Accessspecifiersarekeywordsthatdeterminesthetypeofaccesstothememberofaclass.Theseare:
Public
Protected
Private
Defaults
Question:
DescribethewrapperclassesinJava.
Answer:
Wrapperclassiswrapperaroundaprimitivedatatype.Aninstanceofawrapperclasscontains,orwraps,aprimitivevalueofthecorrespondingtype.
Followingtableliststheprimitivetypesandthecorrespondingwrapperclasses:
PrimitiveWrapper
Question:
Readthefollowingprogram:
publicclasstest{
publicstaticvoidmain(String[]args){
intx=3;
inty=1;
if(x=y)
else
}
}
Whatistheresult?
A.Theoutputisequal?
br>B.TheoutputinnotEqual?
br>C.Anerrorat"if(x=y)"causescompilationtofall.
D.Theprogramexecutesbutnooutputisshowonconsole.
Answer:
C
Question:
whatistheclassvariables?
Answer:
Whenwecreateanumberofobjectsofthesameclass,theneachobjectwillshareacommoncopyofvariables.Thatmeansthatthereisonlyonecopyperclass,nomatterhowmanyobjectsarecreatedfromit.Classvariablesorstaticvariablesaredeclaredwiththestatickeywordinaclass,butminditthatitshouldbedeclaredoutsideoutsideaclass.Thesevariablesarestoredinstaticmemory.Classvariablesaremostlyusedforconstants,variablethatneverchangeitsinitialvalue.Staticvariablesarealwayscalledbytheclassname.Thisvariableiscreatedwhentheprogramstartsi.e.itiscreatedbeforetheinstanceiscreatedofclassbyusingnewoperatorandgetsdestroyedwhentheprogramsstops.Thescopeoftheclassvariableissameainstancevariable.Theclassvariablecanbedefinedanywhereatclasslevelwiththekeywordstatic.Itinitialvalueissameasinstancevariable.Whentheclassvariableisdefinedasintthenit'sinitialvalueisbydefaultzero,whendeclaredbooleanitsdefaultvalueisfalseandnullforobjectreferences.Classvariablesareassociatedwiththeclass,ratherthanwithanyobject.
Question:
Whatisthedifferencebetweentheinstanceofandgetclass,thesetwoaresameornot?
Theinstanceofoperatorcomparesanobjecttoaspecifiedtype.Wecanuseittotestifanobjectisaninstanceofaclass,aninstanceofasubclass,oraninstanceofaclassthatimplementsaparticularinterface.WeshouldtrytouseinstanceofoperatorinplaceofgetClass()method.RememberinstanceofopeatorandgetClassarenotsame.Trythisexample,itwillhelpyoutobetterunderstandthedifferencebetweenthetwo.
Interfaceone{
}
ClassTwoimplementsone{
}
ClassThreeimplementsone{
}
publicclassTest{
publicstaticvoidmain(Stringargs[]){
onetest1=newTwo();
onetest2=newThree();
}
}
*Q1.HowcouldJavaclassesdirectprogrammessagestothesystemconsole,buterrormessages,saytoafile?
.
TheclassSystemhasavariableoutthatrepresentsthestandardoutput,andthevariableerrthatrepresentsthestandarderrordevice.Bydefault,theybothpointatthesystemconsole.Thishowthestandardoutputcouldbere-directed:
Streamst=newStream(newFileOutputStream("output.txt"));System.setErr(st);System.setOut(st);
*Q2.What'sthedifferencebetweenaninterfaceandanabstractclass?
A.Anabstractclassmaycontaincodeinmethodbodies,whichisnotallowedinaninterface.Withabstractclasses,youhavetoinherityourclassfromitandJavadoesnotallowmultipleinheritance.Ontheotherhand,youcanimplementmultipleinterfacesinyourclass.
*Q3.Whywouldyouuseasynchronizedblockvs.synchronizedmethod?
A.Synchronizedblocksplacelocksforshorterperiodsthansynchronizedmethods.
*Q4.Exp
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