1.3. The layers of Android

The Android stack includes an impressive array of features for mobile applications. In fact, looking at the architecture alone, without the context of Android being a platform designed for mobile environments, it would be easy to confuse Android with a general computing environment. All the major components of a computing platform are there. Here’s a quick rundown of prominent components of the Android stack:

• A Linux kernel that provides a foundational hardware abstraction layer, as well as core services such as process, memory, and filesystem management. The kernel is where hardware-specific drivers are implemented—capabilities such as Wi-Fi and Bluetooth are here. The Android stack is designed to be flexible, with many optional components that largely rely on the availability of specific hardware on a given device. These components include features such as touch screens, cameras, GPS receivers, and accelerometers.

• Prominent code libraries, including the following:

  • Browser technology from WebKit, the same open source engine powering Mac’s Safari and the iPhone’s Mobile Safari browser. WebKit has become the de facto standard for most mobile platforms.

  • Database support via SQLite, an easy-to-use SQL database.

  • Advanced graphics support, including 2D, 3D, animation from Scalable Games Language (SGL), and OpenGL ES.

  • Audio and video media support from PacketVideo’s OpenCORE, and Google’s own Stagefright media framework.

  • Secure Sockets Layer (SSL) capabilities from the Apache project.

• An array of managers that provide services for

  • Activities and views

  • Windows

  • Location-based services

  • Telephony

  • Resources

• The Android runtime, which provides

  • Core Java packages for a nearly full-featured Java programming environment. Note that this isn’t a Java ME environment.

  • The Dalvik VM, which employs services of the Linux-based kernel to provide an environment to host Android applications.