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1、GenericsintheJavaProgrammingLanguageGiladBrachaJuly5,2004Contents1Introduction22DefiningSimpleGenerics33GenericsandSubtyping44Wildcards54.1BoundedWildcards...........................65GenericMethods76InteroperatingwithLegacyCode106.1UsingLegacyCodeinGenericCode........

2、..........106.2ErasureandTranslation.........................126.3UsingGenericCodeinLegacyCode..................137TheFinePrint147.1AGenericClassisSharedbyallitsInvocations............147.2CastsandInstanceOf..........................147.3Arrays........................

3、..........158ClassLiteralsasRun-timeTypeTokens169MoreFunwithWildcards189.1WildcardCapture............................2010ConvertingLegacyCodetoUseGenerics2011Acknowledgements2311IntroductionJDK1.5introducesseveralextensionstotheJavaprogramminglanguage.Oneoftheseisthei

4、ntroductionofgenerics.Thistutorialisaimedatintroducingyoutogenerics.Youmaybefamiliarwithsimilarconstructsfromotherlanguages,mostnotablyC++templates.Ifso,you’llsoonseethattherearebothsimilaritiesandimportantdifferences.Ifyouarenotfamiliarwithlook-a-alikeconstructsfrome

5、lsewhere,allthebetter;youcanstartafresh,withoutunlearninganymisconceptions.Genericsallowyoutoabstractovertypes.Themostcommonexamplesarecon-tainertypes,suchasthoseintheCollectionhierarchy.Hereisatypicalusageofthatsort:ListmyIntList=newLinkedList();//1myIntList.add(newI

6、nteger(0));//2Integerx=(Integer)myIntList.iterator().next();//3Thecastonline3isslightlyannoying.Typically,theprogrammerknowswhatkindofdatahasbeenplacedintoaparticularlist.However,thecastisessential.ThecompilercanonlyguaranteethatanObjectwillbereturnedbytheiterator.Toe

7、nsuretheassignmenttoavariableoftypeIntegeristypesafe,thecastisrequired.Ofcourse,thecastnotonlyintroducesclutter.Italsointroducesthepossibilityofaruntimeerror,sincetheprogrammermightbemistaken.Whatifprogrammerscouldactuallyexpresstheirintent,andmarkalistasbeingrestrict

8、edtocontainaparticulardatatype?Thisisthecoreideabehindgenerics.Hereisaversionoftheprogramfragmentgivenaboveusinggenerics:Lis