Android Architecture Android

What is Android Architecture?

The operating system of Android is a stack of software components which is divided into five sections and four main layers.

What is Android Architecture?

Linux kernel

  • From the above figure you can see that the bottom of the layers is Linux Kernel - Linux 3.6 with approximately 115 patches.
  • A level of abstraction is provided between the device hardware and it contains all the essential hardware drivers like camera, keypad, display etc.
  • The kernel also handles all the networking and a vast array of device drivers, which take the pain out of interfacing to peripheral hardware.

Libraries

The set of libraries contain on top of Linux kernel where it contains open-source Web browser engine WebKit, well known library libc, SQLite database which is a useful repository for storage and sharing of application data, libraries to play and record audio and video, SSL libraries responsible for Internet security etc.

Android Libraries

The Java-based libraries specific to Android development are explained in this. For example libraries include the application framework libraries in addition to those that facilitate user interface building, graphics drawing and database access. A summary of some key core Android libraries available to the Android developer is as follows:

  • 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.

The above Android libraries are the Java-based core libraries in the Android runtime.

Android Runtime

  • The Android Runtime is available on the second layer from the bottom.
  • It provides a key component called Dalvik Virtual Machine which is a kind of Java Virtual Machine specially designed and optimized for Android.
  • This Dalvik Virtual Machine makes use of Linux core features like memory management and multi-threading, which is intrinsic in the Java language.
  • It enables every Android application to run in its own process, with its own instance of the Dalvik virtual machine.
  • It also provides a set of core libraries to enable Android application developers for writing Android applications using standard Java programming language.

Application Framework

The Application Framework layer provides higher-level services to applications in the form of Java classes. Application developers are allowed to make use of these services in their applications.
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

Android applications will be at the top layer.The applications are written which are to be installed on this layer only. For example applications like Contacts Books, Browser, and Games etc.


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