The Android system implements the principle of least privilege. That is, each app, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an app can’t access parts of the system it is not given permission for.

App components are the essential building blocks of an Android app. Each component is an entry point through which the system or a user can enter your app. Some components depend on others.

There are four types of app components:

• Activities
• Services
• Broadcast receivers
• Content providers