java面试题和答案(英文版)

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1、Java面试题和答案（英文版）Q:WhatisthedifferencebetweenanInterfaceandanAbstractclass?A:Anabstractclasscanhaveinstancemethodsthatimplementadefaultbehavior.AnInterfacecanonlydeclareconstantsandinstancemethods,butcannotimplementdefaultbehaviorandallmethodsareimplicitlyabstract.Aninterfacehasallpublic

2、membersandnoimplementation.Anabstractclassisaclasswhichmayhavetheusualflavorsofclassmembers(private,protected,etc.),buthassomeabstractmethods.Q:WhatisthepurposeofgarbagecollectioninJava,andwhenisitused?A:Thepurposeofgarbagecollectionistoidentifyanddiscardobjectsthatarenolongerneededbya

3、programsothattheirresourcescanbereclaimedandreused.AJavaobjectissubjecttogarbagecollectionwhenitbecomesunreachabletotheprograminwhichitisused.Q:Describesynchronizationinrespecttomultithreading.A:Withrespecttomultithreading,synchronizationisthecapabilitytocontroltheaccessofmultiplethrea

4、dstosharedresources.Withoutsynchonization,itispossibleforonethreadtomodifyasharedvariablewhileanotherthreadisintheprocessofusingorupdatingsamesharedvariable.Thisusuallyleadstosignificanterrors.Q:Explaindifferentwayofusingthread?A:Thethreadcouldbeimplementedbyusingrunnableinterfaceorbyi

5、nheritingfromtheThreadclass.Theformerismoreadvantageous,'causewhenyouaregoingformultipleinheritance..theonlyinterfacecanhelp.Q:Whatarepassbyreferenceandpassbyvalue?A:PassByReferencemeansthepassingtheaddressitselfratherthanpassingthevalue.PassbyValuemeanspassingacopyofthevaluetobepassed

6、.Q:WhatisHashMapandMap?A:MapisInterfaceandHashmapisclassthatimplementsthat.Q:DifferencebetweenHashMapandHashTable?A:TheHashMapclassisroughlyequivalenttoHashtable,exceptthatitisunsynchronizedandpermitsnulls.(HashMapallowsnullvaluesaskeyandvaluewhereasHashtabledoesntallow).HashMapdoesnot

7、guaranteethattheorderofthemapwillremainconstantovertime.HashMapisunsynchronizedandHashtableissynchronized.Q:DifferencebetweenVectorandArrayList?A:Vectorissynchronizedwhereasarraylistisnot.Q:DifferencebetweenSwingandAwt?A:AWTareheavy-weightcomponenets.Swingsarelight-weightcomponents.H