吴裕雄--天生自然JAVA面向对象高级编程学习笔记：instanceof关键字

class A{                    // 定义类A
    public void fun1(){        // 定义fun1()方法
        System.out.println("A --> public void fun1(){}") ;
    }
    public void fun2(){
        this.fun1() ;        // 调用fun1()方法
    }
};
class B extends A{
    public void fun1(){        // 此方法被子类覆写了
        System.out.println("B --> public void fun1(){}") ;
    }
    public void fun3(){
        System.out.println("B --> public void fun3(){}") ;
    }
};
public class InstanceofDemo01{
    public static void main(String asrgs[]){
        A a1 = new B() ;        // 通过向上转型实例化对象
        System.out.println("A a1 = new B()：" + (a1 instanceof A)) ;
        System.out.println("A a1 = new B()：" + (a1 instanceof B)) ;
        A a2 = new A() ;        // 通过向上转型实例化对象
        System.out.println("A a2 = new B()：" + (a2 instanceof A)) ;
        System.out.println("A a2 = new B()：" + (a2 instanceof B)) ;
    }
};

class A{                    // 定义类A
    public void fun1(){        // 定义fun1()方法
        System.out.println("A --> public void fun1(){}") ;
    }
    public void fun2(){
        this.fun1() ;        // 调用fun1()方法
    }
};
class B extends A{
    public void fun1(){        // 此方法被子类覆写了
        System.out.println("B --> public void fun1(){}") ;
    }
    public void fun3(){
        System.out.println("B --> public void fun3(){}") ;
    }
};
class C extends A{
    public void fun1(){        // 此方法被子类覆写了
        System.out.println("C --> public void fun1(){}") ;
    }
    public void fun5(){
        System.out.println("C --> public void fun5(){}") ;
    }
};
public class InstanceofDemo02{
    public static void main(String asrgs[]){
        fun(new B()) ;
        fun(new C()) ;
    }
    public static void fun(A a){
        a.fun1() ;
        if(a instanceof B){
            B b = (B) a ;
            b.fun3() ;
        }
        if(a instanceof C){
            C c = (C) a ;
            c.fun5() ;
        }
    }
};