多态多态多态多态 的 向上转型 一个小栗子....

public class Main {

    public static void main(String[] args) {
        test test = new test();
        test.xxx(new zi());


    }
}

class fu{
    public void x(){
        System.out.println("我是父");
    }
}

class zi extends fu{
    public void x(){
        System.out.println("我重写了父类的x方法");
    }
    public void xx(){
        System.out.println("我是子");
    }
}

class test{
    public void xxx(fu xxx){
        xxx.x();
    }
}