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java 多态

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

package text5;

public class Father {
public void say(){
    System.out.println("father say()");
}
public static void main(String[] args) {
    Father son=new Son();
    son.say();
}
}

class Son extends Father{
    public void say(){
        System.out.println("son say()");
    }
}

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有时候使用向上转型会丢掉子类特有的方法，

package text5;

public class Father {
public void say(){
    System.out.println("father say()");
}
public static void main(String[] args) {
    Father son=new Son();
    son.sayMe();
}
}

class Son extends Father{
    public void say(){
        System.out.println("son say()");
    }
    public void sayMe(){
        System.out.println("son sayMe");
    }
}

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2.向下转型（强转）注意强转的方法

package text5;

public class Father {
    public void say() {
        System.out.println("father say()");
    }

    public static void main(String[] args) {
        // 向上转型
        Father son = new Son();
        son.say();

        // 向下转型
        Son son2 = (Son) son;
        son2.sayMe();
    }
}

class Son extends Father {
    public void say() {
        System.out.println("son say()");
    }

    public void sayMe() {
        System.out.println("son sayMe");
    }
}

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动态绑定;

package text5;

public class Father {
    public void say() {
        System.out.println("father say()");
    }

    public static void main(String[] args) {
        // 向上转型
        Father son = new Son();
        son.say();

    }
}

class Son extends Father {
    public void say() {
        System.out.println("son say()");
    }

    public void sayMe() {
        System.out.println("son sayMe");
    }
}

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静态绑定;!!!!

package text5;

public class Father {
    private String name = "father";

    public static void say() {
        System.out.println("father say()");
    }

    public void say1() {
        System.out.println("father say1()");
    }

    /// 主运行程序
    public static void main(String[] args) {
        // 向上转型
        Father son = new Son();
        System.out.println(son.name);
        son.say1();
        son.say();

        Son f = (Son) son;
        f.say();
        f.say1();
    }
}

class Son extends Father {
    String name = "Son";

    public static void say() {
        System.out.println("son say()");
    }

    public void say1() {
        System.out.println("son say1");
    }
}

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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:

package Animal2;

public abstract class Pet {
    private String name;
    private int health;
    private int love;

    public Pet() {
    }

    public Pet(String name, int health, int love) {
        this.name = name;
        this.health = health;
        this.love = love;
    }

    public void print() {
        System.out.println("宠物的自白：");
        System.out.print("我的名字叫" + getName() + "，健康值是" + getHealth() + "，和主人的亲密度是" + getLove());
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getHealth() {
        return health;
    }

    public void setHealth(int health) {
        // 设置默认
        if (health < 0 || health > 100)
            health = 60;
        this.health = health;
    }

    public int getLove() {
        return love;
    }

    public void setLove(int love) {
        if (love < 0 || love > 100)
            love = 60;
        this.love = love;
    }

    public abstract void eat();
}

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Dog

package Animal2;

public class Dog extends Pet {
    private String strain;

    public Dog(String name, int health, int love) {
        super(name, health, love);
        // this.strain = strain;
    }

    public Dog(String name, int health, int love, String strain) {
        super(name, health, love);
        this.strain = strain;
    }

    // 接飞盘
    public void getFrise() {
        System.out.println("接飞盘啊");
    }

    public Dog() {
        // TODO Auto-generated constructor stub
    }

    public void print() {
        System.out.println("宠物的自白");
        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()
                + ",我是一只酷酷的" + strain);
    }

    public String getStrain() {
        return strain;
    }

    public void setStrain(int strain) {
        if(strain==1){
        this.strain = "拉布拉多";
        }else this.strain="博美";
    }

    @Override
    public void eat() {
        // TODO Auto-generated method stub
        if(getHealth()==100){
            System.out.println("狗狗已经饱了，不需要吃东西了。");
        }else {
            System.out.println("带狗狗去吃骨头......");
            setHealth(getHealth() + 3);
            System.out.println("狗狗的健康值为："+getHealth());
        }
    }

}

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Penguin

package Animal2;

public class Penguin extends Pet {
    String sex;

    public Penguin(String name, int health, int love, String sex) {
        super(name, health, love);
        this.sex = sex;
    }

    public Penguin(String name, int health, int love) {
        super(name, health, love);
        // this.sex=sex;
    }

    public Penguin() {
        // TODO Auto-generated constructor stub
    }

    public void swim() {
        System.out.println("会游泳啊");
    }

    public void print() {
        System.out.println("宠物的自白");
        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() + ",性别是" + sex);
    }

    public void setSex(int sex) {
        if (sex == 1) {
            this.sex = "Q仔";
            return;
        }
        this.sex = "Q妹";
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public void eat() {
        // TODO Auto-generated method stub
        if (getHealth() == 100) {
            System.out.println("企鹅已经饱了，不需要吃东西了。");
        } else {
            System.out.println("带企鹅去吃骨头......");
            setHealth(getHealth() + 5);
            System.out.println("qie的健康值为：" + getHealth());
        }
    }

}

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Master:

package Animal2;

//主人与宠物玩
public class Master {
    public void play(Pet pet) {
        if (pet instanceof Dog) {
            Dog dog = (Dog) pet;
            dog.getFrise();
        } else if (pet instanceof Penguin) {
            Penguin pen = (Penguin) pet;
            pen.swim();
        }
    }

    // 喂食物
    public void feed(Pet pet) {
        if (pet instanceof Dog) {
            Dog dog = (Dog) pet;
            dog.eat();
        } else if (pet instanceof Penguin) {
            Penguin penguin = (Penguin) pet;
            penguin.eat();
        }
    }
}

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Test:

package Animal2;

import java.util.Scanner;

public class Text {
    public static void main(String[] args) {
    Master master=new Master();
    Pet dog=new Dog();
    dog.setName("黑比");
    dog.setLove(68);
    dog.setHealth(0);
    ((Dog) dog).setStrain(1);//儿子的调用强转
    master.feed(dog);
    dog.print();
    System.out.println("*********************");
    
    Pet penguin=new Penguin();
    penguin.setName("QQ");
    penguin.setHealth(100);
    penguin.setLove(76);
    ((Penguin) penguin).setSex(1);//儿子的调用
    penguin.print();
    
    }
}

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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:

package Car;

/**
 * 汽车抽象类
 * 
 * @author Administrator
 *
 */
public abstract class Vehicle {
    private String no;
    private String brand;

    // 有参构造
    public Vehicle(String no, String brand) {
        this.brand = brand;
        this.no = no;
    }

    // 抽象方法，计算汽车租赁价格
    public abstract int cale(int days);

    // 自动获取的方法
    public String getNo() {
        return no;
    }

    public void setNo(String no) {
        this.no = no;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

}

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Bus；

package Car;

public class Bus extends Vehicle {
    private int seat;// 座位数

    // 构造不要忘了
    public Bus(String no, String brand, int seat) {
        super(no, brand);// 自动
        this.seat = seat;
        // TODO Auto-generated constructor stub
    }

    @Override
    public int cale(int days) {
        if (seat < 16)
            return days * 800;
        else
            return days * 1500;
    }

    public int getSeat() {
        return seat;
    }

    public void setSeat(int seat) {
        this.seat = seat;
    }

}

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Car：

package Car;

/**
 * 轿车类
 * 
 * @author Administrator
 *
 */
public class Car extends Vehicle {
    private String type;// 汽车型号

    public Car(String no, String brand, String type) {
        super(no, brand);
        this.type = type;
    }

    @Override
    public int cale(int days) {
        if ("1".equals(type)) {// 代表550i
            return days * 500;
        } else if ("2".equals(type)) {
            return days * 600;
        } else
            return 300 * days;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

}

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Truck:

package Car;

/**
 * 计算总的租价
 * 
 * @author Administrator
 *
 */
public final class Truck extends Vehicle {
    int ton;// 吨位

    public Truck(String no, String brand, int ton) {
        super(no, brand);
        this.ton = ton;
    }

    @Override
    public int cale(int days) {
        // TODO Auto-generated method stub
        return days * ton;
    }
}

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Customer:

package Car;


public class Customer {
private String id;
private String name;
public Customer(String id,String name){
    this.name=name;
    this.id=id;
}
public int calcTotalRent(Vehicle motos[],int days){    
    int sum=0;
    for(int i=0;i<motos.length;i++)
    sum+=motos[i].cale(days);
    return sum;
 }
public String getId() {
    return id;
}
public void setId(String id) {
    this.id = id;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}

}

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Test:

package Car;

import java.util.Scanner;

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

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案例一：

Animal:

package text2;

public class Animal {
private String name;
private int age;

public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public int getAge() {
    return age;
}
public void setAge(int age) {
    this.age = age;
}
public void cry(){
    System.out.println("不知道怎么叫");
    
}
}

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Cat:

package text2;

public class Cat extends Animal{
    
public void cry(){
    System.out.println("喵喵叫");
}
}

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Dog;

package text2;

public class Dog extends Animal{
public void cry(){
    System.out.println("汪汪叫");
}
}

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Test:

package text2;

public class Tset {
public static void main(String[] args){
    Cat cat=new Cat();
    cat.cry();
    Dog dog=new Dog();
    dog.cry();
    Animal an=new Cat();
    an.cry();
    an=new Dog();
    an.cry();
}
}

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案例二;

Animal:

package text2;

public class Animal {
private String name;
private int age;

public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public int getAge() {
    return age;
}
public void setAge(int age) {
    this.age = age;
}
public void cry(){
    System.out.println("不知道怎么叫");
    
}
public void eat(){
    
}
}

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Cat；

package text2;

public class Cat extends Animal{
    
public void cry(){
    System.out.println("喵喵叫");
}
public void eat(){
    System.out.println("猫喜欢吃鱼");
}
}

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Dog:

package text2;

public class Dog extends Animal{
public void cry(){
    System.out.println("汪汪叫");
}
public void eat(){
    System.out.println("狗喜欢吃骨头");
}
}

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Food；

package text2;

public class Food {
String name;
public void showname(){
    
}

}

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Fish:

Bone；

package text2;

public class Bone extends Food{
public void showname(){
System.out.println("我是骨头");    
}

}

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MAster:

package text2;

public class Master {
//给动物喂食物
    public void feed(Animal an,Food f)//灵活
        {
        an.eat();
        f.showname();
    }
    
}

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Test;

package text2;

public class Tset {
public static void main(String[] args){
    Master master=new Master();
    master.feed(new Dog(), new Bone());
    
}
}

View Code

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原文地址：https://www.cnblogs.com/helloworld2019/p/10622555.html