class Animal {
    public void eat() {
        System.out.println("吃饱饭");
    }
}

class Dog extends Animal {
    public void play() {
        System.out.println("狗咬人");
    }
}

class Worf extends Animal {
    public void play() {
        System.out.println("狼吃人");
    }
}

class Demo1 {
    public static void main(String[] args) {
        Animal a = new Worf();
        System.out.println(a instanceof Dog);
        if (a instanceof Dog) {
            Dog d = (Dog) (a);
        } else {
            Worf w = (Worf) (a);
            w.play();
        }

    }

}

Animal a = new Worf();我们之前写这个东西写的很自然这其实是对象的上转型。a instanceof Dog，这个是在问a是Dog类型的吗？Dog d = (Dog) (a);这个就是下转型了。