(1)Context:-
The Context is the central command center for an Android application .All application -specific functionality can be accessed through the context.
(2)Activity:-
An Android Application is a collection of tasks, each of which is called an Activity.Each Activity Within an Application has a unique task or purpose.
(3)Intent:-
The android operating system uses an asynchronous messaging mechanism to much task requests with the appropriate Activity.Each request is packaged is as an Intent You can think of each such request as a message stating an intent to do something.
(4)Service:-
Tasks that do not require user interaction can be encapsulated in a service.A service is most useful when the operation are lengthy(offloading time-consuming processing)or need to be done regularly(such a checking a server for new mail).
