看不懂。。，
把别人的链接放在这。
【转载自】
https://wenku.baidu.com/view/3d4894bb7c1cfad6195fa7e8.html
https://blog.csdn.net/mingtian715/article/details/51243000
https://blog.csdn.net/lanchunhui/article/details/51175136
https://wenku.baidu.com/view/28aaf753964bcf84b8d57b37.html
https://www.cnblogs.com/byeyear/p/7725592.html
https://blog.csdn.net/qq_23660243/article/details/80203987
https://blog.csdn.net/weixin_41730407/article/details/80455612
http://blog.sina.com.cn/s/blog_bb81c2230102xdbl.html