Dev Guide_Android Basics_Application Fundamenta

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Application Fundamentals

Android applications are written in the Java programming language. The Android SDK tools compile the code—along with any data and resource files—into an Android package, an archive file with an .apk suffix. All the code in a single .apk file is considered to be one application and is the file that Android-powered devices use to install the application.

應用程序原理

Android 應用程序是用java語言寫的。Android SDK工具把代碼數據和資源文件都編譯成一個以.apk爲後綴的Android存檔文件包。應用程序的全部代碼都在一個.apk文件裏，而且它能夠安裝在Android平臺。

 

Once installed on a device, each Android application lives in its own security sandbox:

• The Android operating system is a multi-user Linux system in which each application is a different user.
• By default, the system assigns each application a unique Linux user ID (the ID is used only by the system and is unknown to the application). The system sets permissions for all the files in an application so that only the user ID assigned to that application can access them.
• Each process has its own virtual machine (VM), so an application's code runs in isolation from other applications.
• By default, every application runs in its own Linux process. Android starts the process when any of the application's components need to be executed, then shuts down the process when it's no longer needed or when the system must recover memory for other applications.

每一個安裝在設備上的應用程序都運行在它本身的安全區間內：

由於Android操做系統是一個多用戶的操做系統，因此每一個應用程序都是一個不一樣的用戶。

默認的，系統分配給每一個應用程序一個惟一的Linux用戶ID（ID只對系統使用，對應用程序不可見）。系統在一個應用程序內爲全部的文件設置了權限，因此只有被分配了用戶ID的應用程序才能訪問它們。

每一個進程有本身的虛擬機，因此每一個應用程序的運行都是相互隔離的。

默認的，每一個應用程序都在本身的Linux進程下運行。當應用程序的組件須要執行的時候，Android開啓了進程，當再也不須要，或者必須爲其餘應用程序回收內存時，關閉了進程。

未完待續。。。