概述
Java中的Class类有两个重要的方法：cast()和asSubclass()。这两个方法都是用于Class类进行运行时(run-time)阶段的类型转换的。下面来看看他们的定义和使用：
第一个方法asSubclass()
public <U> Class<? extends U> asSubclass(Class<U> clazz)
Casts this Class object to represent a subclass of the class represented by the specified class object. Checks that that the cast is valid, and throws a ClassCastException if it is not. If this method succeeds, it always returns a reference to this class object.
This method is useful when a client needs to "narrow" the type of a Class object to pass it to an API that restricts the Class objects that it is willing to accept. A cast would generate a compile-time warning, as the correctness of the cast could not be checked at runtime (because generic types are implemented by erasure).
Returns:
this Class object, cast to represent a subclass of the specified class object.
Throws:
ClassCastException - if this Class object does not represent a subclass of the specified class (here "subclass" includes the class itself).
Since:
1.5
使用实例：
Class<?> c = Class.forName(“MyClass”);
Class<Child> child = c.asSubClass(Father.class); // “Child” extends “Father”
第二个方法cast()
public T cast(Object obj)
Casts an object to the class or interface represented by this Class object.
Parameters:
obj - the object to be cast
Returns:
the object after casting, or null if obj is null
Throws:
ClassCastException - if the object is not null and is not assignable to the type T.
Since:
1.5
使用实例：
这个函数可以简单的理解为将一个Object类型的对象转换成Class表示的类型的对象（其实在java中Class类就是所有类型字节码的一种抽象，或者简单理解为在java中就是用于来说明类型的类型，因为java中一切都是类，所以“类”（类型）也是是类，而这个类就是Class）。
Class<String> c = String.class;
Object o = “hello world!”;
String s = c.cast(o); // 将Object类型转成这里的Class表示的类型，即String类型
Java中的Class类可以表示java中的所有类型，主要通过Class<T>中的T来指定具体表示的是哪种类型。
最后
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