Android is a mobile operating system (OS) based on the Linux kernel and currently developed by Google. With a user interface based on direct manipulation, Android is designed primarily for touchscreen mobile devices such as smartphones and tablet computers, with specialized user interfaces for televisions (Android TV), cars (Android Auto), and wrist watches (Android Wear). The OS uses touch inputs that loosely correspond to real-world actions, like swiping, tapping, pinching, and reverse pinching to manipulate on-screen objects, and a virtual keyboard. Despite being primarily designed for touchscreen input, it also has been used in game consoles, digital cameras, regular PCs and other electronics.
The Android software development kit (SDK) includes a comprehensive set of development tools. These include a debugger, libraries, a handset emulator based on QEMU, documentation, sample code, and tutorials. Currently supported development platforms include computers running Linux (any modern desktop Linux distribution), Mac OS X 10.5.8 or later, and Windows XP or later. For the moment one can also develop Android software on Android itself by using the AIDE - Android IDE - Java, C++ app and the Java editor app.
The Android Debug Bridge (ADB) is a toolkit included in the Android SDK package. It consists of both client and server-side programs that communicate with one another. The ADB is typically accessed through the command-line interface, although numerous graphical user interfaces exist to control ADB.
Fastboot is a diagnostic protocol included with the SDK package used primarily to modify the flash filesystem via a USB connection from host computer. It requires that the device be started in a boot loader or Second Program Loader mode in which only the most basic hardware initialization is performed. After enabling the protocol on the device itself, it will accept a specific set of commands sent to it via USB using a command line. Some of the most commonly used fastboot commands include:
flash – rewrites a partition with a binary image stored on the host computer
erase – erases a specific partition
reboot – reboots the device into either the main operating system, the system recovery partition or back into its bootloader
devices – displays a list of all devices (with the serial number) connected to the host computer
format – formats a specific partition; the file system of the partition must be recognized by the device
Libraries written in C, C++ and other languages can be compiled to ARM, MIPS or x86 native code and installed using the Android Native Development Kit. Native classes can be called from Java code running under the Dalvik VM using the System.loadLibrary call, which is part of the standard Android Java classes
Complete applications can be compiled and installed using traditional development tools. However, according to the Android documentation, NDK should not be used solely for developing applications only because the developer prefers to program in C/C++, as using NDK increases complexity while most applications would not benefit from using it.
The ADB debugger gives a root shell under the Android Emulator which allows ARM, MIPS or x86 native code to be uploaded and executed. Native code can be compiled using GCC or the Intel C++ Compiler on a standard PC. Running native code is complicated by Android's use of a non-standard C library (libc, known as Bionic). The graphics library that Android uses to arbitrate and control access to this device is called the Skia Graphics Library (SGL), and it has been released under an open source licence. Skia has backends for both Win32 and Unix, allowing the development of cross-platform applications, and it is the graphics engine underlying the Google Chrome web browser