https://www.zhihu.com/question/25414422
http://blog.csdn.net/kun1234567/article/details/7917847
http://blog.csdn.net/adambieber/article/details/46733661
http://liweizhaolili.blog.163.com/blog/static/1623074420145110502776/
http://blog.csdn.net/u014635337/article/details/45439877
http://shadowkong.com/archives/2136