Java学习记录(补充四:面向对象的多态和接口)

面对对象的多态


//多态
//如何实现多态:
//1:使用集成
//2:子类重写父类的方法
//3;父类引用子类对象
package day8;

public abstract class Instrument {
    public abstract void  play(); 

}

package day8;

public class Piano extends Instrument{

    @Override
    public void play() {
        System.out.println("月光曲!");
    }
    
}

package day8;

public class Violin extends Instrument{

    @Override
    public void play() {
        System.out.println("葫芦娃!");
    }

}

package day8;

public class Artist {
    //Instrument instrument = new piano();(只用来理解)
    public void make(Instrument instrument) {
        instrument.play();
    }
}

package day8;

public class Test {
    public static void main(String[] args) {
        Artist user1 = new Artist();
        //实例化对象=是赋值,后面是实例化一个对象,前面是用来接收的
        Piano piano = new Piano();
        Violin violin = new Violin();
        user1.make(piano);
        user1.make(violin);
    }
}

结果图:

练习:租用车(轿车和客车)
package day8_2;

public abstract class MotoVechicle {
    private String no;
    private String brand;
    private String color;
    private String mileage;
    
    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;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getMileage() {
        return mileage;
    }

    public void setMileage(String mileage) {
        this.mileage = mileage;
    }
    
    public MotoVechicle() {
        super();
    }

    public MotoVechicle(String no, String brand, String color, String mileage) {
        super();
        this.no = no;
        this.brand = brand;
        this.color = color;
        this.mileage = mileage;
    }

    public abstract int calcRent(int day);
}

package day8_2;

public class Car extends MotoVechicle{
    private String type;
    
    public String getType() {
        return type;
    }

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

    @Override
    public int calcRent(int day) {
        int price = 0;
        if (type.equals("GL8")) {
            price = 600 * day;
        }else if(type.equals("BMW")){
            price = 500 * day;
        }else if (type.equals("Buick")) {
            price = 300 * day;
        } 
        return price;
    }
    

}

package day8_2;

public class Bus extends MotoVechicle{
    private int seatCount;
    
    public int getSeatCount() {
        return seatCount;
    }
    public void setSeatCount(int seatCount) {
        this.seatCount = seatCount;
    }
    
    public Bus(int seatCount) {
        super();
        this.seatCount = seatCount;
    }
    public Bus(int seatCount,String no, String brand, String color, String mileage) {
        super(no,brand,color,mileage);
        this.seatCount = seatCount;
    }
    @Override
    public int calcRent(int day) {
        int price = 0;
        if (seatCount > 16) {
            price = 1500 * day;
        }else if (seatCount <= 16) {
            price = 800 * day;
        }
        return price;
    }

}

package day8_2;

public class CalcTest {
    public int calc(MotoVechicle motoVehicle,int day){
        int price = motoVehicle.calcRent(day);
        return price;
    }
    public static void main(String[] args) {
        int result = 0;
        Car car = new Car("GL8");
        CalcTest calcPrice = new CalcTest();
        result = calcPrice.calc(car, 7);
        System.out.println("租两天GL8的价格为："+result);
    }
}

结果图:

面对对象接口

//接口:接口是一种规范
//接口不可以被实例化
//接口里面的方法都是抽象的
package day8_3;

public interface InterfaceDemo {
    //1:接口不能被实例化
    //2:接口里面的方法默认都是public类型的抽象方法
    //所有public abstract修饰可以忽略
    //3:类是单继承 但是类可以实现多个接口
    //4:在接口里定义的属性都是public类型的静态常量
    // public static final可以省略
    //5:接口可以继承多个接口,可以得到父级接口里面的"所有"的属性和方法
     public static final int AGE = 10;
     void showName();
}

package day8_3;

public class UDisk implements UsbInterface {

    public void service() {
        System.out.println("连接USB接口,开始传输数据");
    }
    public static void main(String[] args) {
        //多态的一种,向上转型(多态就是"父类引用子类对象!!!")
        UsbInterface uDisk = new UDisk();
        uDisk.service();
    }
}

package day8_3;

public interface UsbInterface {
    void service();
}

结果图: