1.Java基础-多态性

 

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向上转型：

 

 

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向下转型：

 

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多态性的应用：

package com.jikexueyuan.pol;


class A1{
    public void tell1() {
        System.out.println("A -- tell1");
    }
}
class B1 extends A1{
    public void tell2() {
        System.out.println("A -- tell2");
    }
}

class C1 extends A1{
    public void tell3() {
        System.out.println("A -- tell3");
    }
}
//以上是比较繁琐的调用方式
class D1 extends A1{
    
}



public class PolDemo02 {

    public static void main(String[] args) {
        say(new B1());    //都是调用父类A1的代码而并没有调用自己的代码tell2
        say(new C1());    //都是调用父类A1的代码而并没有调用自己的代码tell3
        
        //以上要是有100个类，那岂不是要调用100个方法？，所以
        say(new D1());
    }
    
//    public static void say(B1 b) {
//        b.tell1();
//    }
//    public static void say(C1 c) {
//        c.tell1();
//    }
    
    
//以上要是有100个类，那岂不是要调用100个方法？，所以要运用到对象多态性来调用：
    public static void say(A1 a) {
        a.tell1();    
    }
    
    

}

 

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instanceof关键字：

 

 

 

 

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抽象类的应用：

 

 

 

package com.jikexueyuan.pol;


abstract class Person{
    private int age;
    private String name;
    
    public Person(int age,String name) {
        this.age = age;
         = name;
    }
    
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
         = name;
    }
    
    public abstract void want();
    
}

class Student extends Person{
    //学生有自己的属性score(成绩)
    private int score;
    
    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }

    //复写父类的抽象方法：
    public Student(int age, String name,int score) {
        super(age, name);
        this.score = score;
        // TODO Auto-generated constructor stub
    }
    
    //父类中有构造方法，所以子类也要复写构造方法：
    public void want() {
        System.out.println("姓名："+ getName() + "年龄：" + getAge() +"成绩" + getScore() );
        
    }
    
}

class Worker extends Person{

    private int money;
    
    
    public int getMoney() {
        return money;
    }


    public void setMoney(int money) {
        this.money = money;
    }

    //构造方法
    public Worker(int age, String name,int money) {
        super(age, name);
        this.money = money;
        // TODO Auto-generated constructor stub
    }
    
    public void want() {
        System.out.println("姓名："+ getName() + "年龄：" + getAge() +"工资" + getMoney() );
    }
    
}


public class AbsDemo01 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Student s = new Student(10,"小明",100);
        s.want();
        Worker w = new Worker(30,"大明",1000);
        w.want();
    }

}


//不要去继承已经完成好的类

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面向对象接口的使用：

package com.jikexueyuan.pol;

interface USB{
    void start();
    void stop();
}

class C{
    public static void work(USB u) {
        u.start();
        System.out.println("工作中");
        u.stop();
    }
}

class USBDisk implements USB{

    @Override
    public void start() {
        System.out.println("U盘开始工作");
        
    }

    @Override
    public void stop() {
        System.out.println("U盘停止工作");
        
    }
    
}

class Printer implements USB{

    @Override
    public void start() {
        System.out.println("打印机工作");
        
    }

    @Override
    public void stop() {
        System.out.println("打印机停止工作");
        
    }
    
}
public class InterDemo01 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        C.work(new USBDisk());
        C.work(new Printer());
    }

}