Java的回调机制下

水深无声 2021-09-20 09:02 350阅读 0赞

**一 代码**

import java.awt.Rectangle;
    interface Measurer
    {
        // 这个anObject，并不明确。不明确的用意是，先不绑定任何特定的对象
        double measure( Object anObject );
    }
    // 把抽象的measure方法具体化
    class AreaMeasurer implements Measurer
    {
        public double measure(Object anObject)
        {
            // 把抽象的对象明确化，由于Object对象是所有对象的鼻祖，所以，它可以化身任何对象
            Rectangle aRectangle = (Rectangle) anObject;
            double area = aRectangle.getWidth() * aRectangle.getHeight();
            return area;
        }
    }
    class Car
    {  
        private double price;
        private double taxRate;
        
        Car(double price, double taxRate)
        {
            this.price = price;
            this.taxRate = taxRate;
        }
        public double getPrice()
        {
            return price;
        }
        public double getRate()
        {
            return taxRate;
        }
    }
    class CarMeasurer implements Measurer
    {
    
        public double measure(Object anObject)
        {
            Car aCar = (Car) anObject;
            double totalPrice = aCar.getPrice() * (1 + aCar.getRate());
            return totalPrice;
        }
    }
    class Data
    {
        public static double average(Object[] objects, Measurer meas)   // 前者提供数据，后者提供方法
        {
            double sum = 0.0;
            for (Object obj : objects)
            {
                sum = sum + meas.measure(obj);
            }
            if (objects.length > 0)
            {
                return sum / objects.length;
            } else {
                return 0;
            }
        }
    }
    public class callBackDemo
    {
        public static void main(String[] args)
        {
            Measurer areaMeas = new AreaMeasurer();
            Rectangle[] rects = new Rectangle[]
            {
                new Rectangle(5, 10, 20, 30),
                new Rectangle(10, 20, 30, 40),
                new Rectangle(20, 30, 5, 15)
            };
            double averageArea = Data.average(rects, areaMeas);
            System.out.println("average area is: " + averageArea);
                    
            Measurer carMeas = new CarMeasurer();
            Car[] cars = new Car[]
            {
                new Car(20000, 0.12),
                new Car(30000, 0.16),
                new Car(90000, 0.18),
            };
            double averagePrice = Data.average(cars, carMeas);
            System.out.println("average price is: " + averagePrice);
        }
    }

**二 运行**

average area is: 625.0
    average price is: 54466.666666666664

**三 图解**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70]: /images/20210724/217e1a1318644d1d9342644b792fec02.png