Android 开发文档 程序基础——Shutting down components

content provider只会在回应ContentReslover发出的请求时激活，而broadcast
receiver只在回应广播消息时激活，所以没有必要关闭这些组件。

另一方面，activity用来生成用户界面，长时间的与用户对话，甚至空闲时也保持活动，只要对话还在继续。相似的，service也会保持长时
间的运行。所以android提供了方法来关闭activity和service。

activity可以通过调用finish()来关闭。一个activity可以通过调用finishActivty()关闭另一个
activty（它通过startActivityForResult()
运行起来的
）。

service可以通过调用自身的stopSelf()来停止，或者Context.stopService().

转自我的android博客

原文

Shutting down components

A content provider is active only while it’s responding to a request
from a ContentResolver. And a broadcast receiver is active only while
it’s responding to a broadcast message. So there’s no need to
explicitly shut down these components.

Activities, on the other hand, provide the user interface. They’re
in a long-running conversation with the user and may remain active,
even when idle, as long as the conversation continues. Similarly,
services may also remain running for a long time. So Android has
methods to shut down activities and services in an orderly way:

An activity can be shut down by calling its finish()
method. One activity
can shut down another activity (one it started with startActivityForResult()
) by
calling finishActivity()
.

A service can be stopped by calling its stopSelf()
method, or by calling Context.stopService()
.

Components might also be shut down by the system when they are no
longer being used or when Android must reclaim memory for more active
components. A later section, Component Lifecycles, discusses this
possibility and its ramifications in more detail.