Activity : An Activity is the screen representation of any application in Android. Each activity has a layout file where you can place your UI.
Content Provider : Content providers share data between applications.
Service : It is a component that runs in the background to perform long-running operations without interacting with the user and it even works if application is destroyed.
Broadcast Receivers : It respond to broadcast messages from other applications or from the system itself. These messages are sometime called events or intents.
