Understanding the Android Framework

What is android
Android is a software stack for mobile devices that includes an operating system, middleware and key applications.

Features

 * Application framework enabling reuse and replacement of components


 * Dalvik virtual machine optimized for mobile devices


 * Integrated browser based on the open source WebKit engine


 * Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional)


 * SQLite for structured data storage


 * Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)


 * GSM Telephony (hardware dependent)


 * Bluetooth, EDGE, 3G, and WiFi (hardware dependent)


 * Camera, GPS, compass, and accelerometer (hardware dependent)


 * Rich development environment including a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE

Application Framework
Developers have full access to the same framework APIs used by the core applications. The application architecture is designed to simplify the reuse of components; any application can publish its capabilities and any other application may then make use of those capabilities (subject to security constraints enforced by the framework). This same mechanism allows components to be replaced by the user.

Underlying all applications is a set of services and systems, including:


 * A rich and extensible set of Views that can be used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser


 * Content Providers that enable applications to access data from other applications (such as Contacts), or to share their own data


 * A Resource Manager, providing access to non-code resources such as localized strings, graphics, and layout files


 * A Notification Manager that enables all applications to display custom alerts in the status bar


 * An Activity Manager that manages the life cycle of applications and provides a common navigation backstack