class Demo_Poymorphic {
    public static void main(String[] args) {
        Cat c = new Cat();
        Animal a = new Cat();
        c.eat();
        a.eat();
}
}
class Animal {
    public void eat() {
    System.out.println("动物吃饭");
    }
}
class Cat extends Animal  {
    public void eat() {
    System.out.println("猫吃鱼");
    }
}

这里输出的都是猫吃鱼.