Key Components in Android

Activity:

Your application presentation layer.The UI of your application i sbuilt around one or more extensions of the activity class. Activities useViews,Framents to display information.Activity is equal to html forms.

Example: Login window, settings screen.,etc.

Services:

The invisible workers of your application.It will run without UI.It will trigger notifications,update data sources and broadcasting intents.
Example: alarm, phone call,weather reports.,ect.

Content Providers:

Sharable persistent data storage.Content providers manage and persist application data and typically interact with SQL Databases. You can configure your application's Content Providers to allow access from other applications,and you can access the content providers exposed by others.

Intent:

A powerful interapplication message-passing framework.Intents are used throughout the android application.You can use Intents to Start or to Stop Activities and Services. One of the most common use of intents to start new activity ,either Explicitly(by specifying the class to load) or Implicitly(by requesting that an action be performed on a piece of data).

Example: 1)Display a webpage. 2)Dial a phone call.

View:

A view is a component ,it means a UI element such as Button,TextEdit.,etc.

Fragments:

it is a collection of activities, displays one or more activities on the same screen,at the same time.

AndroidManifest.xml:

It is a root file of android application such as web.xml in servlets.It contains inforamtion aboutpermissions,Content Providers.,etc

Android Virtual Device:

It is used to test the application in your laptop/computer without using mobiles or ipad's.