Android App Development
Android is an operating system based on Linux with a Java programming interface. The Android Software Development Kit provides all necessary tools to develop Android applications. This includes a compiler, debugger, and a device emulator, as well as its own virtual machine to run Android programs. Android is currently primarily developed by Google.
Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database. Android applications consist of different components and can reuse components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task. For example, you can trigger from your application another application which has it registered with the Android system to handle photos. In this other application, you select a photo and return to your application to use the selected photo.
Android Development Tools:
• The Android Software Development Kit (SDK) contains the necessary tools to create, compile and package Android application. Most of these tools are command line based. The Android SDK also provides an Android device emulator, so that Android applications can be tested without a real Android phone.
• You can create Android virtual devices (AVD) via the Android SDK, which runs in this emulator. The Android SDK contains the Android debug bridge tool which allows connecting to a virtual or real Android device
• Google provides the Android Development Tools (ADT) to develop Android applications with Eclipse. ADT is a set of components (plug-ins) which extend the Eclipse IDE with Android development capabilities. ADT contains all required functionalities to create, compile, debug and deploy Android applications from the Eclipse IDE.
• ADT also allows creating and start AVDs. The Android Development Tools (ADT) provides specialized editors for resources files, these editors allow switching between the XML representation of the file and a richer user interface via tabs on the bottom of the editor. The Android system uses a special virtual machine, i.e. the Dalvik Virtual Machine to run Java based applications.
• Dalvik uses an own bytecode format which is different from Java bytecode. Therefore, you cannot directly run Java class files on Android; they need to get converted to the Dalvik bytecode format.
• The Android SDK contains a tool called dx which converts Java class files into a .dex (DalvikExecutable) file. All class files of one application are placed in one compressed .dexfile. During this conversion process, redundant information in the class files is optimized in the .dexfile. For example, if the same String is found in different class files, the dex file contains an only once reference of this String.