Application Fundamentals Android applications are written in the Java programming language. The compiled Java code — along with any data and resource files required by the application — is bundled by the aapt tool into an Android package, an archive file marked by an .apk suffix. This file is the vehicle for distributing the application and installing it on mobile devices; it's the file users download to their devices. All the code in a single .apk file is considered to be one application. Android 应用基础：Android 应用程序是通过 java 语言开发的，通过绑定一些应用所需要的东西，例如：编译的 Java 代码，加上数据和一些资源文件，使用一个 apt 的工具将所有的东西封装成一个android 包，这个文件的文件后缀是.apk。这个文件是分发并安装应用程序到移动设备的载体，是用户获得该应用程序所需要的下载的文件。Application Components A central feature of Android is that one application can make use of elements of other applications (provided those applications permit it). For example, if your application needs to display a scrolling list of images and another application has developed a suitable scroller and made it available to others, you can call upon that scroller to do the work, rather than develop your own. Your application doesn't incorporate the code of the other application or link to it. Rather, it simply starts up that piece of the other application when the need arises. For this to work, the system must be able to start an application process when any part of it is needed, and instantiate the Java objects for that part. Therefore, unlike applications on most other systems, Android applications don't have a single entry point for everything in the application (no main() function, for example). Rather, they have essential components tha...
