package com.ithema_46;

public  abstract class Animal {
    public abstract void eat();
}

package com.ithema_46;
/*
  测试类
  方法的形参是抽象类名，其实需要的是该抽象类的子类对象
  方法的返回值是抽象类名，其实返回的是该抽象类的子类对象
 */
public class AnimalDemo {
    public static void main(String[] args) {
        //创建操作对象，并调用方法
        AnimalOperator ao = new AnimalOperator();
        Animal a = new Cat();
        ao.useAnimal(a);

        Animal a2 = ao.getAnimal();//new Cat()
        a2.eat();

    }
}

package com.ithema_46;

public class AnimalOperator {
    public void useAnimal(Animal a){ //Animal a = new Cat();
        a.eat();
    }
    public Animal getAnimal(){
        Animal a = new Cat();
        return a;

    }
}

package com.ithema_46;

public class Cat extends  Animal{
    @Override
    public void eat() {
        System.out.println("猫吃鱼");
    }
}