安桌应用基础

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1、英语原文AndroidApplicationFundamentalsAndroidapplicationsarewrittenintheJavaprogramminglanguage.TheAndroidSDKtoolscompilethecode—alongwithanydataandresourcefiles—intoanAndroidpackage^anarchivefilewithan.apksuffix.Allthecodeinasingle.apkfileisconsideredtobeoneapplicationandisthefilethatAndroid-powered

2、devicesusetoinstalltheapplication.Onceinstalledonadevice,eachAndroidapplicationlivesinitsownsecuritysandbox:•TheAndroidoperatingsystemisamulti-userLinuxsysteminwhicheachapplicationisadifferentuser.•Bydefault,thesystemassignseachapplicationauniqueLinuxuserID(theIDisusedonlybythesystemandisunknownt

3、otheapplication).ThesystemsetspermissionsforallthefilesinanapplicationsothatonlytheuserIDassignedtothatapplicationcanaccessthem.•Eachprocesshasitsownvirtualmachine(VM),soanapplication^coderunsinisolationfromotherapplications.口•Bydefault,everyapplicationrunsinitsownLinuxprocess.Androidstartsthepro

4、cesswhenanyoftheapplication^componentsneedtobeexecuted,thenshutsdowntheprocesswhenitfsnolongerneededorwhenthesystemmustrecovermemoryforotherapplications.Inthisway,theAndroidsystemimplementstheprincipleofleastprivilege.Thatis,eachapplication,bydefault,hasaccessonlytothecomponentsthatitrequirestodo

5、itsworkandnomore.Thiscreatesaverysecureenvironmentinwhichanapplicationcannotaccesspartsofthesystemforwhichitisnotgivenpermission.However,therearewaystoranapplicationtosharedatawithotherapplicationsandtoranapplicationtoaccesssystemservices:•Il'spossibletoarrangefortwoapplicationstosharethesameLinu

6、xuserID、inwhichcasetheyareabletoaccesseacholherfstiles.Toconservesystemresources,applicationswiththesameuserIDcanalsoarrangetoruninthesameLinuxprocessandsharethesameVM(theapplicationsmustalsobesignedwiththesamecertificate)-•Anapplicationcanrequestpermissiontoaccessdevicedatasuchastheuser'scontact

7、s,SMSmessages,themountablestorage(SOcard),camera.Bluetooth,andmore.Allapplicationpermissionsmustbegrantedbytheuseratinstalltime.ThatcoversthebasicsregardinghowanAndroidapplicationexistswithinthesystem.Therestofthisdocu