Four(4) building blocks of Android are: activity, service, broadcast, content provider.
- An activity is a screen displaying user interface controls and/or graphical content. Most apps are made up of multiple independent activities.
- A service handles long-running background tasks, without displaying a user interface. Services can be either started and run until completion, or bound to an activity to take part in IPC (inter-process communication).
- Broadcast receivers: notification of system events such as battery low or device shutdown. You can also create a broadcast receiver to listen for your own custom events.
- A content provider manages data that other applications can query and update. The data is typically stored in the file system or in SQLite database.