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1、┊┊┊┊┊┊┊┊┊┊┊┊┊装┊┊┊┊┊订┊┊┊┊┊线┊┊┊┊┊┊┊┊┊┊┊┊┊附录二英文原文及译文ApplicationFundamentalsAndroidapplicationsarewrittenintheJavaprogramminglanguage.ThecompiledJavacode—alongwithanydataandresourcefilesrequiredbytheapplication—isbundledbytheaapttoolintoanAndroidpackage,anarchivefilemarkedbyan.apksuff
2、ix.Thisfileisthevehiclefordistributingtheapplicationandinstallingitonmobiledevices;it'sthefileusersdownloadtotheirdevices.Allthecodeinasingle.apkfileisconsideredtobeoneapplication.Inmanyways,eachAndroidapplicationlivesinitsownworld:1.Bydefault,everyapplicationrunsinitsownLinuxproc
3、ess.Androidstartstheprocesswhenanyoftheapplication'scodeneedstobeexecuted,andshutsdowntheprocesswhenit'snolongerneededandsystemresourcesarerequiredbyotherapplications.2.Eachprocesshasitsownvirtualmachine(VM),soapplicationcoderunsinisolationfromthecodeofallotherapplications.3.Bydef
4、ault,eachapplicationisassignedauniqueLinuxuserID.Permissionsaresetsothattheapplication'sfilesarevisibleonlytothatuserandonlytotheapplicationitself—althoughtherearewaystoexportthemtootherapplicationsaswell.It'spossibletoarrangefortwoapplicationstosharethesameuserID,inwhichcasetheyw
5、illbeabletoseeeachother'sfiles.Toconservesystemresources,applicationswiththesameIDcanalsoarrangetoruninthesameLinuxprocess,sharingthesameVM.ApplicationComponentsAcentralfeatureofAndroidisthatoneapplicationcanmakeuseofelementsofotherapplications(providedthoseapplicationspermitit).F
6、orexample,ifyourapplicationneedstodisplayascrollinglistofimagesandanotherapplicationhasdevelopedasuitablescrollerandmadeitavailabletoothers,youcancalluponthatscrollertodothework,ratherthandevelopyourown.Yourapplicationdoesn'tincorporatethecodeoftheotherapplicationorlinktoit.Rather
7、,itsimplystartsupthatpieceoftheotherapplicationwhentheneedarises.Forthistowork,thesystemmustbeabletostartanapplicationprocesswhenanypartofitisneeded,andinstantiatetheJavaobjectsforthatpart.Therefore,unlikeapplicationsonmostothersystems,Androidapplicationsdon'thaveasingleentrypoint
8、foreverythingintheapplication(nom
