已经定义B类型

class A1 {
    public void fun1(){
        System. out.println("A-->public void fun1(){}");
    }
public void fun2(){
    this .fun1 ();
}
};
class B  extends A1{
     —
已经定义类型B
    public void fun1(){
        System.out.println("B-->public void funl(){}");
    }
    public void fun3(){
        System.out.println("B-->public void fun3(){}");
    }
};
 class PolDemo02{
    public static void main(String[] args){
        A  a = (A) new B();
        B b  =(B)a;
        b.fun1();
        b.fun2();
        b.fun3();
        
        
    }
}