class

http://blog.csdn.net/wklken/article/details/6313265

http://www.cnblogs.com/longdouhzt/archive/2012/05/16/2505141.html

http://www.jb51.net/article/51108.htm

http://jingyan.baidu.com/article/066074d671e150c3c21cb0be.html