java 多态 优势

1.因为多态,不需要为每一个类型定义方法

package com;

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

class Cat extends Animal {
    
    
    public void eat() {
    
    
        System.out.println("Cat eat");
    }
}
class Dog extends Animal {
    
    
    public void eat() {
    
    
        System.out.println("Dog eat");
    }
}


public class App2 {
    
    
    public static void showCatEat (Cat c){
    
    
        c.eat();
    }
    public static void showDogEat (Dog d){
    
    
        d.eat();
    }
    public static void showAnimalEat (Animal a){
    
    
        a.eat();
    }
    public static void main(String[] args) {
    
    
        Cat c = new Cat();
        Dog d = new Dog();
        showCatEat(c);
        showDogEat(d);

        //用多态的方式,参数是Animal,会自动将Cat和Dog转换为Animal,而Animal调用时,因为多态执行的又是Cat和Dog的eat
        //这样就不需要定义多种参数类型的方法了
        showAnimalEat(c);
        showAnimalEat(d);
    }


}

2.因为多态,可以将多个类型保存到列表中

package com;

import java.util.LinkedList;
import java.util.List;

public class App2 {
    
    
    public static void main(String[] args) {
    
    
        List<Object> list = new LinkedList<>();
        list.add("123");
        System.out.println(list.get(0).toString()); //123
        System.out.println(new Object().toString()); //java.lang.Object@29453f44
    }
}

当我们将String填入到列表时,自动转型为Object,调用toString方法,因为多态调用的还是String的toString