For Android applications, each window is called an activity. From a programming point of view, an activity is a class that extends the Activity class. Unlike other systems in which a program contains several windows displayed simultaneously, in Android, the screen is always occupied by a single window. Moreover, windows are connected by the simple fact that a window generates several windows. The window that appears on the screen when the application is started is considered the main activity that generates all the others. To create an activity, we need to create a class that extends the Activity class. At startup, the program will generate it, and we can interact with the window through events.

Some of the most important events are:

• onCreate
• onPause

public class MainActivity extends Activity {
 
   @Override
   public void onCreate(Bundle savedInstanceState)
   {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);        
   }
   @Override
   protected void onPause() 
   {
       // TODO Auto-generated method stub
       super.onPause();
   }
 
}