android使用finish()和System.exit()退出应用程序的理解

this.finish() in Activity only stop and destroy this activity, application still staying background (check by hold HOME button)
I used:
System.exit(0);
but it still appear there!
That's how Android works. The user/developer is not given any way to actually exit the application. When you call 'finish', the application stack is just pushed to the background. It still exists in the memory. Android itself decides when to close the application(i.e. remove its instance from the memory) and generally this is done when your application becomes the oldest application which was not used for the longest time.

this.finish()主要是对Activity，当前的Activity结束了，但是整个Application还是在内存中运行，此时Application就成为了background进程，System.exit(0)是结束当前进程