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Java 多态

Wesley13

2021-10-11

1458 0 0

类型的检测——向上转型 向下转型

向上转型：父类对象的引用指向子类对象，向下转型：向上转型的基础上再次指向子类的对象

1.向上转型

1package text5;
2
3public class Father {
4public void say(){
5    System.out.println("father say()");
6}
7public static void main(String[] args) {
8    Father son=new Son();
9    son.say();
10}
11}
12
13class Son extends Father{
14    public void say(){
15        System.out.println("son say()");
16    }
17}

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有时候使用向上转型会丢掉子类特有的方法，

1package text5;
2
3public class Father {
4public void say(){
5    System.out.println("father say()");
6}
7public static void main(String[] args) {
8    Father son=new Son();
9    son.sayMe();
10}
11}
12
13class Son extends Father{
14    public void say(){
15        System.out.println("son say()");
16    }
17    public void sayMe(){
18        System.out.println("son sayMe");
19    }
20}

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2.向下转型（强转）注意强转的方法

1package text5;
2
3public class Father {
4    public void say() {
5        System.out.println("father say()");
6    }
7
8    public static void main(String[] args) {
9        // 向上转型
10        Father son = new Son();
11        son.say();
12
13        // 向下转型
14        Son son2 = (Son) son;
15        son2.sayMe();
16    }
17}
18
19class Son extends Father {
20    public void say() {
21        System.out.println("son say()");
22    }
23
24    public void sayMe() {
25        System.out.println("son sayMe");
26    }
27}

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动态绑定;

1package text5;
2
3public class Father {
4    public void say() {
5        System.out.println("father say()");
6    }
7
8    public static void main(String[] args) {
9        // 向上转型
10        Father son = new Son();
11        son.say();
12
13    }
14}
15
16class Son extends Father {
17    public void say() {
18        System.out.println("son say()");
19    }
20
21    public void sayMe() {
22        System.out.println("son sayMe");
23    }
24}

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静态绑定;!!!!

1package text5;
2
3public class Father {
4    private String name = "father";
5
6    public static void say() {
7        System.out.println("father say()");
8    }
9
10    public void say1() {
11        System.out.println("father say1()");
12    }
13
14    /// 主运行程序
15    public static void main(String[] args) {
16        // 向上转型
17        Father son = new Son();
18        System.out.println(son.name);
19        son.say1();
20        son.say();
21
22        Son f = (Son) son;
23        f.say();
24        f.say1();
25    }
26}
27
28class Son extends Father {
29    String name = "Son";
30
31    public static void say() {
32        System.out.println("son say()");
33    }
34
35    public void say1() {
36        System.out.println("son say1");
37    }
38}

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1.使用多态实现主人给宠物喂食：

2.使用多态实现主人领养宠物并与宠物玩耍

3.使用多态计算汽车租赁总租金

4.使用多态完善汽车租赁系统计价

父亲不能调用儿子的方法，需要强制转换

A.实现主人给宠物喂食：

Pet:

1package Animal2;
2
3public abstract class Pet {
4    private String name;
5    private int health;
6    private int love;
7
8    public Pet() {
9    }
10
11    public Pet(String name, int health, int love) {
12        this.name = name;
13        this.health = health;
14        this.love = love;
15    }
16
17    public void print() {
18        System.out.println("宠物的自白：");
19        System.out.print("我的名字叫" + getName() + "，健康值是" + getHealth() + "，和主人的亲密度是" + getLove());
20    }
21
22    public String getName() {
23        return name;
24    }
25
26    public void setName(String name) {
27        this.name = name;
28    }
29
30    public int getHealth() {
31        return health;
32    }
33
34    public void setHealth(int health) {
35        // 设置默认
36        if (health < 0 || health > 100)
37            health = 60;
38        this.health = health;
39    }
40
41    public int getLove() {
42        return love;
43    }
44
45    public void setLove(int love) {
46        if (love < 0 || love > 100)
47            love = 60;
48        this.love = love;
49    }
50
51    public abstract void eat();
52}

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Dog

1package Animal2;
2
3public class Dog extends Pet {
4    private String strain;
5
6    public Dog(String name, int health, int love) {
7        super(name, health, love);
8        // this.strain = strain;
9    }
10
11    public Dog(String name, int health, int love, String strain) {
12        super(name, health, love);
13        this.strain = strain;
14    }
15
16    // 接飞盘
17    public void getFrise() {
18        System.out.println("接飞盘啊");
19    }
20
21    public Dog() {
22        // TODO Auto-generated constructor stub
23    }
24
25    public void print() {
26        System.out.println("宠物的自白");
27        System.out.println("我的名字叫" + this.getName() + ",健康值是" + this.getHealth() + "和主人的亲密度是" + this.getLove()
28                + ",我是一只酷酷的" + strain);
29    }
30
31    public String getStrain() {
32        return strain;
33    }
34
35    public void setStrain(int strain) {
36        if(strain==1){
37        this.strain = "拉布拉多";
38        }else this.strain="博美";
39    }
40
41    @Override
42    public void eat() {
43        // TODO Auto-generated method stub
44        if(getHealth()==100){
45            System.out.println("狗狗已经饱了，不需要吃东西了。");
46        }else {
47            System.out.println("带狗狗去吃骨头......");
48            setHealth(getHealth() + 3);
49            System.out.println("狗狗的健康值为："+getHealth());
50        }
51    }
52
53}

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Penguin

1package Animal2;
2
3public class Penguin extends Pet {
4    String sex;
5
6    public Penguin(String name, int health, int love, String sex) {
7        super(name, health, love);
8        this.sex = sex;
9    }
10
11    public Penguin(String name, int health, int love) {
12        super(name, health, love);
13        // this.sex=sex;
14    }
15
16    public Penguin() {
17        // TODO Auto-generated constructor stub
18    }
19
20    public void swim() {
21        System.out.println("会游泳啊");
22    }
23
24    public void print() {
25        System.out.println("宠物的自白");
26        System.out.println(
27                "我的名字叫" + this.getName() + ",健康值是" + this.getHealth() + "和主人的亲密度是" + this.getLove() + ",性别是" + sex);
28    }
29
30    public void setSex(int sex) {
31        if (sex == 1) {
32            this.sex = "Q仔";
33            return;
34        }
35        this.sex = "Q妹";
36    }
37
38    public void setSex(String sex) {
39        this.sex = sex;
40    }
41
42    @Override
43    public void eat() {
44        // TODO Auto-generated method stub
45        if (getHealth() == 100) {
46            System.out.println("企鹅已经饱了，不需要吃东西了。");
47        } else {
48            System.out.println("带企鹅去吃骨头......");
49            setHealth(getHealth() + 5);
50            System.out.println("qie的健康值为：" + getHealth());
51        }
52    }
53
54}

View Code

Master:

1package Animal2;
2
3//主人与宠物玩
4public class Master {
5    public void play(Pet pet) {
6        if (pet instanceof Dog) {
7            Dog dog = (Dog) pet;
8            dog.getFrise();
9        } else if (pet instanceof Penguin) {
10            Penguin pen = (Penguin) pet;
11            pen.swim();
12        }
13    }
14
15    // 喂食物
16    public void feed(Pet pet) {
17        if (pet instanceof Dog) {
18            Dog dog = (Dog) pet;
19            dog.eat();
20        } else if (pet instanceof Penguin) {
21            Penguin penguin = (Penguin) pet;
22            penguin.eat();
23        }
24    }
25}

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Test:

1package Animal2;
2
3import java.util.Scanner;
4
5public class Text {
6    public static void main(String[] args) {
7    Master master=new Master();
8    Pet dog=new Dog();
9    dog.setName("黑比");
10    dog.setLove(68);
11    dog.setHealth(0);
12    ((Dog) dog).setStrain(1);//儿子的调用强转
13    master.feed(dog);
14    dog.print();
15    System.out.println("*********************");
16    
17    Pet penguin=new Penguin();
18    penguin.setName("QQ");
19    penguin.setHealth(100);
20    penguin.setLove(76);
21    ((Penguin) penguin).setSex(1);//儿子的调用
22    penguin.print();
23    
24    }
25}

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B.使用多态实现汽车总租金

首先定义一个机动车抽象类，

Vehicle:

1package Car;
2
3/**
4 * 汽车抽象类
5 * 
6 * @author Administrator
7 *
8 */
9public abstract class Vehicle {
10    private String no;
11    private String brand;
12
13    // 有参构造
14    public Vehicle(String no, String brand) {
15        this.brand = brand;
16        this.no = no;
17    }
18
19    // 抽象方法，计算汽车租赁价格
20    public abstract int cale(int days);
21
22    // 自动获取的方法
23    public String getNo() {
24        return no;
25    }
26
27    public void setNo(String no) {
28        this.no = no;
29    }
30
31    public String getBrand() {
32        return brand;
33    }
34
35    public void setBrand(String brand) {
36        this.brand = brand;
37    }
38
39}

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Bus；

1package Car;
2
3public class Bus extends Vehicle {
4    private int seat;// 座位数
5
6    // 构造不要忘了
7    public Bus(String no, String brand, int seat) {
8        super(no, brand);// 自动
9        this.seat = seat;
10        // TODO Auto-generated constructor stub
11    }
12
13    @Override
14    public int cale(int days) {
15        if (seat < 16)
16            return days * 800;
17        else
18            return days * 1500;
19    }
20
21    public int getSeat() {
22        return seat;
23    }
24
25    public void setSeat(int seat) {
26        this.seat = seat;
27    }
28
29}

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Car：

1package Car;
2
3/**
4 * 轿车类
5 * 
6 * @author Administrator
7 *
8 */
9public class Car extends Vehicle {
10    private String type;// 汽车型号
11
12    public Car(String no, String brand, String type) {
13        super(no, brand);
14        this.type = type;
15    }
16
17    @Override
18    public int cale(int days) {
19        if ("1".equals(type)) {// 代表550i
20            return days * 500;
21        } else if ("2".equals(type)) {
22            return days * 600;
23        } else
24            return 300 * days;
25    }
26
27    public String getType() {
28        return type;
29    }
30
31    public void setType(String type) {
32        this.type = type;
33    }
34
35}

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Truck:

1package Car;
2
3/**
4 * 计算总的租价
5 * 
6 * @author Administrator
7 *
8 */
9public final class Truck extends Vehicle {
10    int ton;// 吨位
11
12    public Truck(String no, String brand, int ton) {
13        super(no, brand);
14        this.ton = ton;
15    }
16
17    @Override
18    public int cale(int days) {
19        // TODO Auto-generated method stub
20        return days * ton;
21    }
22}

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Customer:

1package Car;
2
3
4public class Customer {
5private String id;
6private String name;
7public Customer(String id,String name){
8    this.name=name;
9    this.id=id;
10}
11public int calcTotalRent(Vehicle motos[],int days){    
12    int sum=0;
13    for(int i=0;i<motos.length;i++)
14    sum+=motos[i].cale(days);
15    return sum;
16 }
17public String getId() {
18    return id;
19}
20public void setId(String id) {
21    this.id = id;
22}
23public String getName() {
24    return name;
25}
26public void setName(String name) {
27    this.name = name;
28}
29
30}

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Test:

1package Car;
2
3import java.util.Scanner;
4
5public class Test {
6    public static void main(String[] args) {
7        int days;// 租赁天数
8        int totalRent;// 总租赁费用
9        Vehicle motos[] = new Vehicle[5];
10        motos[0] = new Car("宝马x5", "豫DX56432", "1");
11        motos[1] = new Car("宝马x6", "豫DX51112", "2");
12        motos[2] = new Car("金龙", "豫DX99832", "3");
13        motos[3] = new Bus("别克林荫大道", "豫DX99832", 34);
14        motos[4] = new Truck("比亚迪", "豫DX99832", 8);
15        // 控制台输入
16        // 1、客户租赁的多辆汽车信息及租赁天数
17        Customer customer = new Customer("1", "万方");
18        // 2、计算总租赁费用
19        System.out.println("总租金为：" + customer.calcTotalRent(motos, 5));
20    }
21}

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案例一：

Animal:

1package text2;
2
3public class Animal {
4private String name;
5private int age;
6
7public String getName() {
8    return name;
9}
10public void setName(String name) {
11    this.name = name;
12}
13public int getAge() {
14    return age;
15}
16public void setAge(int age) {
17    this.age = age;
18}
19public void cry(){
20    System.out.println("不知道怎么叫");
21    
22}
23}

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Cat:

1package text2;
2
3public class Cat extends Animal{
4    
5public void cry(){
6    System.out.println("喵喵叫");
7}
8}

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Dog;

1package text2;
2
3public class Dog extends Animal{
4public void cry(){
5    System.out.println("汪汪叫");
6}
7}

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Test:

1package text2;
2
3public class Tset {
4public static void main(String[] args){
5    Cat cat=new Cat();
6    cat.cry();
7    Dog dog=new Dog();
8    dog.cry();
9    Animal an=new Cat();
10    an.cry();
11    an=new Dog();
12    an.cry();
13}
14}

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案例二;

Animal:

1package text2;
2
3public class Animal {
4private String name;
5private int age;
6
7public String getName() {
8    return name;
9}
10public void setName(String name) {
11    this.name = name;
12}
13public int getAge() {
14    return age;
15}
16public void setAge(int age) {
17    this.age = age;
18}
19public void cry(){
20    System.out.println("不知道怎么叫");
21    
22}
23public void eat(){
24    
25}
26}

View Code

Cat；

1package text2;
2
3public class Cat extends Animal{
4    
5public void cry(){
6    System.out.println("喵喵叫");
7}
8public void eat(){
9    System.out.println("猫喜欢吃鱼");
10}
11}

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Dog:

1package text2;
2
3public class Dog extends Animal{
4public void cry(){
5    System.out.println("汪汪叫");
6}
7public void eat(){
8    System.out.println("狗喜欢吃骨头");
9}
10}

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Food；

1package text2;
2
3public class Food {
4String name;
5public void showname(){
6    
7}
8
9}

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Fish:

Bone；

1package text2;
2
3public class Bone extends Food{
4public void showname(){
5System.out.println("我是骨头");    
6}
7
8}

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MAster:

1package text2;
2
3public class Master {
4//给动物喂食物
5    public void feed(Animal an,Food f)//灵活
6        {
7        an.eat();
8        f.showname();
9    }
10    
11}

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Test;

1package text2;
2
3public class Tset {
4public static void main(String[] args){
5    Master master=new Master();
6    master.feed(new Dog(), new Bone());
7    
8}
9}

View Code

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