设计模式例子
Reflect on the Visitor design pattern：
http://www.itpub.net/thread-478999-1-11.html#
Patterns & OO Design - Alternative to instanceof for Contracting/Interfaces：
http://forums.sun.com/thread.jspa?threadID=5305575
A Time for Reflection - Java 1.2's reflection capabilities eliminate burdensome accept() methods from your Visitor pattern：
http://www.polyglotinc.com/reflection.html
