How to Develop Android Applications

Android applications are primary written in the Java programming language. The Java source files are converted to Java class files by the Java compiler.

Android provides a tool dx which converts Java class files into a dex (Dalvik Executable) file. All class files of one application are placed in one compressed .dex file. During this conversion process redundant information in the class files are optimized in the .dex file. For example if the same String in different class file is found, the .dex file is stored only once and reference this String in the corresponding classes. .dex files are therefore much smaller in size then the corresponding class files. The .dex file and the resources of an Android project, e.g. the images and XML files are packed into an .apk (Android Package) file. The program aapt (Android Asset Packaging Tool) perform this packaging.

The resulting .apk file contains all necessary data to run the Android application and can be deployed to an Android device via the \"adb\" tool. The Android Development Tools (ADT) allows that all these steps are performed transparent to the user; either within Eclipse or via the command line.

If you use the ADT tooling you press a button or run a script and the whole Android application (.apk file) will be created and deployed.