application: a map of some components.
generaly,one application ,one process.
generaly,when u close the app just as close all the activity.
the process of application is can not be closed, it will be run in the background all the time.
so, what‘s time the android to closing the process of app?
There is a group of strategy to help me manager the process:
The process has diffrent priority:
1. front process :User can see one of activity of the process and can operate the activity
2.visible process:user can see one of activity of the process but can not operate the activity. like dialog.
3.service process: if one service of app run in the background,
4.background process:The process has no any service is runing. like u opened a activity,then press the home key.
5.empty process: The process has no any activty component exits.
The android kill the process order by the priority.(5,4,3..)but when system has more ram it will be recovery which be killed after a little time.
Android‘s process,布布扣,bubuko.com
原文：http://blog.csdn.net/howlaa/article/details/23048263