https://qooah.com/2011/01/18/%e8%bf%aa%e5%a3%ab%e5%b0%bc%e5%9c%a8%e6%97%a5%e6%9c%ac%e6%8e%a8%e5%87%ba-android%e6%99%ba%e8%83%bd%e6%89%8b%e6%a9%9f/