UI life cycle
All BlackBerry® device applications include an application class that is derived from either the Application class, which is included in the net.rim.device.api.system package, or the UiApplication class, which is included in the net.rim.device.api.ui package. The Application class is the base class for all applications on the device, and applications that are not required to respond to user input should extend this class. The UiApplication class is a subclass of Application, and applications that provide a UI should extend this class.
There are three basic phases to the life cycle of any BlackBerry device application: