hardcore java 学习笔记1

       RTTI(runtime type identification),运行时类型识别。不管我们有没有意识到，这个技术都在JVM中广泛的应用着。每当我们使用getClass()，我们就是在使用RTTI。

       public static final void basicRTTIDemo() {Float y = new Float(15.0);String name = "Fred";System.out.println(y.getClass());System.out.println(name.getClass());}

而cast方法也是以RTTI为基础建立的。

public static final void castingWithRTTI() {A a = null;A a1 = new A();B b = new B();C c = new C();a = (A)b; // no problemb = (B)a; // still no problem, casting back to what it was created as. a = a1; // Same type so no problemObject d = (Object)c; // no problem becasue of implicit inheritancec = (C)d; // casting back}

 

This code shows how to create an object of a subclass,cast it to its base class,and then cast it back to the subclass . RTTI works in the background to ensure that your casting is always legal; in other words,an object can safely be cast only to its own type, or to a type that it is inherited from.