Java(15) 多态

一.多态

   1.1 多态：一个事物的多种形态

   1.2 多态的表现

        行为(方法)多态：重写和重载。

        引用多态(动态绑定):编译时的类型和运行时不一致的这种现象

       例：父类 = 子类

             Pet p = new Dog();

　　向上转型；父类=子类

 　　 例：Pet p = new Dog();

     向下转型：子类 = （子类）父类

        例: Dog d = (Dog)p;

public abstract class Pet {
    private String name;
    private int health=100;
    private int age;
    private int love=50;
    public Pet(){
        
    }
    public Pet(String name,int health,int age,int love){
        this.name = name;
        this.health = health;
        this.age = age;
        this.love = love;
    }
    public String getName(){
        return name;
    }
    public void setName(String name){
        this.name= name;
    }
    public int getHealth(){
        return health;
    }
    public void setHealth(int health){
        this.health = health;
    }
    public int getAge(){
        return age;
    }
    public void setAge(int age){
        this.age = age;
    }
    public int getLove(){
        return love;
    }
    public void setLove(int love){
        this.love = love;
    }
    public void ji(){
        System.out.println("宠物的自白：我的名字叫："+this.name+",年龄为："+this.age+"和主人的亲密度为："+this.love);
    }
    public abstract void eat();
}

public class Dog extends Pet{
    private String strain;
    public Dog(){
        
    }
    public Dog(String name,int health,int age,int love,String strain){
        super(name,health,age,love);
        this.strain = strain;
    }
    public void catchingFlyDisc(){
        System.out.println("接飞盘");
        int health = getHealth();
        health = health-10;
        setHealth(health);
        
        int love = getLove();
        love = love+5;
        setLove(love);
    }
    public void eat(){
        System.out.println("狗狗吃鱼");
    }
    public String getStrain(){
        return strain;
    }
    public void setStrain(String strain){
        this.strain = strain;
    }

}

public class Penguin extends Pet {
    private String sex;
    public Penguin(){
        
    }
    public Penguin(String name,int health,int age,int love,String sex){
        super(name,health,age,love);
        this.sex = sex;
    }
    public void swimming(){
        System.out.println("游泳");
        int health = getHealth();
        health = health-10;
        setHealth(health);
        
        int love = getLove();
        love = love+5;
        setLove(love);
    }
    public void eat(){
        System.out.println("企鹅喝水");
    }
    public String getSex(){
        return sex;
    }
    public void setSex(String sex){
        this.sex = sex;
    }

}

public class Master {
    public void feed(Pet p){
        p.eat();
    }
    public void play(Pet p){
        if(p instanceof Dog ){
            Dog d = (Dog) p;
            d.catchingFlyDisc();
        }else if(p instanceof Penguin){
            Penguin pe = (Penguin) p;
            pe.swimming();
        }
    }
}

public class TestPMPD {
    public static void main(String[] args){
        Master m= new Master();
        //向下转型
        Pet p = new Dog();
        Dog d = (Dog) p;
        m.feed(d);
//        Pet p = new Penguin();
//        m.feed(p);
    }
}

运行结果为： 

  注意：java.lang.ClassCastException:类型转换异常

          父类的运行时类型跟要转成的子类的类型不一致

  注意：引用多态存在继承关系

二.instanceof

  语法： 对象A instanceof 类型B

      判断对象A的类型是否是类型B，是就返回true，否则返回false

例：d instanceof Dog

三.实现多态的2种形式

  a.使用父类作为方法形参实现多态

    public void play(Pet p){...}

  b.使用父类作为方法返回值实现多态

    public Pet getPet(int type){...}