Android is an open Source Operating System for mobile devicessuch as smart phones and tablet computers based on Linux Kernal.Android was developed by the Open Handset Alliance, led by Google, and other companies.
It was established on 5th November, 2007, led by Google. It is committed to advance open standards, provide services and deploy handsets using the Android Plateform.
Android operating system is a stack of software components which is roughly divided into five sections and four main layers as shown below in the architecture diagram.
In android Architecture layers the Bottom Layer is Linux Kernal.This provides basic system functionality like process management, memory management, device management like camera, keypad, display etc.
There is Set of Libraries on the Top of Linux Layer including open-source Web browser engine WebKit, well known library libc, SQLite database.
This is the third section of the architecture and available on the second layer from the bottom.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 Android runtime also provides a set of core libraries which enable Android application developers to write Android applications using standard Java programming language.
The Application Framework layer provides many higher-level services to applications in the form of Java classes. Application developers are allowed to make use of these services in their applications.
You will find all the Android application at the top layer. You will write your application to be installed on this layer only. Examples of such applications are Contacts Books, Browser, Games etc.
There are Four Basic Andxroid Application components.They are Activities,Services,Content Provider and roadcast Reciever.
An activity represents a single screen with a user interface through which user interacts with Application.If an application has more than one activity, then one of them should be marked as the activity that is presented when the application is launched.
A service is a component that runs in the background to perform long-running operations. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity.
A content provider component supplies data from one application to others on request. Such requests are handled by the methods of the ContentResolver class. The data may be stored in the file system, the database or somewhere else entirely.
Broadcast Receivers simply respond to broadcast messages from other applications or from the system. For example, applications can also initiate broadcasts to let other applications know that some data has been downloaded to the device and is available for them to use, so this is broadcast receiver who will intercept this communication and will initiate appropriate action.
Tags: Introduction to Android