Android operating system is divided into 5 sections. They are :
Linux kernel : Linux provides a level of abstraction between the device hardware and it contains all the essential hardware drivers like camera, keypad, display etc. Also, the kernel handles all the things that Linux is really good at such as networking and a vast array of device drivers.
Libraries : open-source Web browser engine WebKit, well known library libc, SQLite database which come under libraries is useful for storage and sharing of application data.
Android libraries : These libraries are specific to Android application development. Libraries that facilitate user interface building, graphics drawing and database access come under this category.android.app − Provides access to the application model and is the cornerstone of all Android applications.
android.content − Facilitates content access, publishing and messaging between applications and application components.
android.database − Used to access data published by content providers and includes SQLite database management classes.
- android.opengl − A Java interface to the OpenGL ES 3D graphics rendering API.
- android.os − Provides applications with access to standard operating system services including messages, system services and inter-process communication.
- android.text − Used to render and manipulate text on a device display.
- android.view − The fundamental building blocks of application user interfaces.
- android.widget − A rich collection of pre-built user interface components such as buttons, labels, list views, layout managers, radio buttons etc.
- android.webkit − A set of classes intended to allow web-browsing capabilities to be built into applications.
Android runtime : This section provides a key component called Dalvik Virtual Machine which is a kind of Java Virtual Machine specially designed and optimized for Android. The Dalvik VM makes use of features like memory management and multi-threading. The Dalvik VM enables every Android application to run in its own process, with its own instance of the Dalvik virtual machine.
Android framework : The Android framework includes the following key services −
- Activity Manager − Controls all aspects of the application lifecycle and activity stack.
- Content Providers − Allows applications to publish and share data with other applications.
- Resource Manager − Provides access to non-code embedded resources such as strings, color settings and user interface layouts.
- Notifications Manager − Allows applications to display alerts and notifications to the user.
- View System − An extensible set of views used to create application user interfaces.
Applications : Applications that are to be installed are written to on this layer.