Learn polymorphism with teacher Wang (iii) conversion of parent class to subclass and instance of operator

Parent class tothe transformation of subclasses andinstanceofoperatorKeynote Teacher: Wang ShaohuaQQGroup number:483773664Learning Goals:

s) Parent and subclass conversions: down conversion

p) Mastering the use of the instanceof operator

First, Problem: Play function for host and pet (i) Demand:

play the game with the dog , the dog's health value is reduced by 5 , with the owner's intimacy increased

playing swimming games with penguins, the Penguin's health value decreased by 5 , with the owner of the increase in intimacy

(ii) Implementation ideas

s) Adding catchingflydisc method to Dog class to realize the function of frisbee;

2) Adding swimming method to Penguin class to realize swimming function;

3) Add the play (Pet Pet) method to the host, if pet is playing a Frisbee game on behalf of Dog , if pet represents Penguin is playing swimming games.

R) Create a test class that creates a master, dog, and Penguin object and invokes the appropriate method to implement the host and pet play function.

(iii) Specific implementation

Follow the steps below to step through the task.

1. Dog

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/**     * 实现接飞盘方法     */    public void catchingFlyDisc() {        System.out.println("狗狗" + this.getName() + "正在接飞盘。");        this.setHealth(this.getHealth()-10);        this.setLove(this.getLove()+5);    }

2. Penguin

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/**    * 实现游泳方法    */   public void swimming() {       System.out.println("企鹅" + this.getName() + "正在游泳。");       this.setHealth(this.getHealth()-10);       this.setLove(this.getLove()+5);   }

3. Master

1234	publicvoidPlay(Pet pet){ //1 判断Pet是什么对象 //2 将Pet转化为具体对象，因为父对象没有办法调用子对象的特有的方法 }

Second, Parent class toConversion of subclasses (downward transition)

Assigns a reference to a subclass object to a parent class reference , called a downward transformation, which must be cast at this time.

(i) Demand

What if you assign a dog object to a Pet type reference variable and want to play a Frisbee game with dog ?

(ii) Realize

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publicclass Test {    public static void main(String[] args) {        Pet pet = newDog(