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1、沈阳建筑大学毕业论文英语原文AndroidApplicationFundamentalsAndroidapplicationsarewrittenintheJavaprogramminglanguage.TheAndroidSDKtoolscompilethecode—alongwithanydataandresourcefiles—intoan Androidpackage,anarchivefilewithan .apk suffix.Allthecodeinasingle .apk fileisconsi
2、deredtobeoneapplicationandisthefilethatAndroid-powereddevicesusetoinstalltheapplication.Onceinstalledonadevice,eachAndroidapplicationlivesinitsownsecuritysandbox:lTheAndroidoperatingsystemisamulti-userLinuxsysteminwhicheachapplicationisadifferentuser.lBydefa
3、ult,thesystemassignseachapplicationauniqueLinuxuserID(theIDisusedonlybythesystemandisunknowntotheapplication).ThesystemsetspermissionsforallthefilesinanapplicationsothatonlytheuserIDassignedtothatapplicationcanaccessthem.lEachprocesshasitsownvirtualmachine(V
4、M),soanapplication'scoderunsinisolationfromotherapplications.lBydefault,everyapplicationrunsinitsownLinuxprocess.Androidstartstheprocesswhenanyoftheapplication'scomponentsneedtobeexecuted,thenshutsdowntheprocesswhenit'snolongerneededorwhenthesystemmustrecove
5、rmemoryforotherapplications.Inthisway,theAndroidsystemimplementsthe principleofleastprivilege.Thatis,eachapplication,bydefault,hasaccessonlytothecomponentsthatitrequirestodoitsworkandnomore.Thiscreatesaverysecureenvironmentinwhichanapplicationcannotaccesspar
6、tsofthesystemforwhichitisnotgivenpermission.However,therearewaysforanapplicationtosharedatawithotherapplicationsandforanapplicationtoaccesssystemservices:lIt'spossibletoarrangefortwoapplicationstosharethesameLinuxuserID,inwhichcasetheyareabletoaccesseachothe
7、r'sfiles.Toconservesystemresources,applicationswiththesameuserIDcanalsoarrangetoruninthesameLinuxprocess共21页第20页沈阳建筑大学毕业论文andsharethesameVM(theapplicationsmustalsobesignedwiththesamecertificate).lAnapplicationcanrequestpermissiontoaccessdevicedatasuchastheus
8、er'scontacts,SMSmessages,themountablestorage(SDcard),camera,Bluetooth,andmore.Allapplicationpermissionsmustbegrantedbytheuseratinstalltime.ThatcoversthebasicsregardinghowanAndroidapplicationexis
