Android- Activity, Services Introduction of concepts

              Android is a java-based operating system that runs on Linux kernel. Android applications are developed using java and also uses an XML based User Interface. The basic building blocks of android includes
1.Activity
2.Service
3.Broadcast Receiver
4.Content Providers

           Activity is the basic building block of visible applications. Every application is composed of an activity or set of activities. Also every screen in an application is an individual activity.
          Services are used to provide background tasks. They do not give any UI.
          Broadcast Receivers are capable of receiving and respond to any announcements by an Intent or system. an Intent is a message passed between components like APIs(but not exactly).
          Content Providers gives a set of data to applications. They can supply data to other applications.

Now to develop an android application we need following tools,
1. JDK- Since we use java for android development-download from here- http://www.oracle.com/technetwork/java/javase/downloads/index.html
2. Android SDK-download from here-http://developer.android.com/sdk/index.html
3. An IDE with Android plugin (Preferably Eclipse)-download from here-http://www.eclipse.org/downloads/

Read the installation manuals and install it. After installing Android SDK manager and AVD manager we can start our own android program.