Examining the Application Life Cycle
The life cycle of an Android application is strictly managed by the system, based on the user's needs, available resources, and so on. A user may want to launch a web browser, for example, but the system ultimately decides whether to start the application. Although the system is the ultimate manager, it adheres to some defined and logical guidelines to determine whether an application can be loaded, paused, or stopped. If the user is currently working with an activity, the system gives high priority to that application.
Conversely, if an activity is not visible and the system determines that an application must be shut down to free up resources, it shuts down the lower-priority application.
Contrast this with ...