工厂模型

参考文章：
http://www.codesky.cn/article/doc/200405/200405137661004.htm
http://www.cnblogs.com/lane_cn/articles/70742.html
http://www.yesky.com/dev/msdn/221/2058721.shtml
http://battler.cnblogs.com/archive/2005/01/25/96954.aspx