Android Functionality :

Just like the midlet, an activity uses a series of functions to interact with the outside world.

At its base, your activity must override the method onCreate. Other functions you’ll want to override are onStop, onPause, onResume, and onKeyDown. These few functions are what will let you tie your activity into the Android handset at large. 

By default, new Android applications created within Eclipse will implement a “Hello, World” application. I’ll show you how to go from this basic application to a fully functional splash screen.