说明：  Java反射机制主要提供了以下功能： 在运行时判断任意一个对象所属的类；在运行时构造任意一个类的对象；在运行时判断任意一个类所具有的成员变量和方法；在运行时调用任意一个对象的方法；生成动态代理。
(Java reflection mechanism provides the following functions: to determine an arbitrary object class at runtime; object to construct an arbitrary class at runtime; judging member variables and methods with an arbitrary class at runtime; method is invoked at runtime an arbitrary object; dynamic proxy.)