java 语言程序设计 第十三章 13.5

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（只是将13.1的内容加以修改，具体的就是 implements Comparable；
然后我又在Rectangle类中重写了toString()方法，下面还给了一个关于Rectangle类的测试类。）

public abstract class CompareGeometricObject     implements Comparable<CompareGeometricObject>{    private String color;    private boolean filled;    private java.util.Date dateCreated;    protected CompareGeometricObject()    {        dateCreated = new java.util.Date();    }    protected CompareGeometricObject(String color, boolean filled)    {        this.color = color;        this.filled = filled;        dateCreated = new java.util.Date();    }    public String getColor()    {        return color;    }    public void setColor(String color)    {        this.color = color;    }    public boolean isFilled()    {        return filled;    }    public void setFilled(boolean filled)    {        this.filled = filled;    }    public java.util.Date getDateCreated()    {        return dateCreated;    }    @Override    public String toString()    {        return "Created on " + dateCreated + "\nColor : " + color + "\n and Filled : " + filled;    }    @Override    public int compareTo(CompareGeometricObject o)    {        if (getArea() < o.getArea())        {            return -1;        }        else if (getArea() > o.getArea())        {            return 1;        }        else            return 0;    }    public static CompareGeometricObject max(CompareGeometricObject o1, CompareGeometricObject o2)    {        if (o1.compareTo(o2) > 0)        {            return o1;        }        else            return o2;    }    public abstract double getArea();    public abstract double getPerimeter();}

public class CompareMyRectangle extends CompareGeometricObject{    private double width;    private double height;    public CompareMyRectangle()    {    }    public CompareMyRectangle(double width, double height)    {        this(width, height, "white", false);    }    public CompareMyRectangle(double width, double height, String color, boolean filled)    {        super(color, filled);        this.width = width;        this.height = height;    }    public double getWidth()    {        return width;    }    public void setWidth(double width)    {        this.width = width;    }    public double getHeight()    {        return height;    }    public void setHeight(double height)    {        this.height = height;    }    @Override    public double getArea()    {        return width * height;    }    @Override    public double getPerimeter()    {        return 2 * (width + height);    }    @Override    public String toString()    {        return super.toString() + "\nMy Rectangle Width : " + getWidth() + " Height : " + getHeight();    }}

import java.util.Scanner;public class TestCompareRectangle{    public static void main(String [] args)    {        Scanner input = new Scanner(System.in);        System.out.print("Create the first Rectangle (enter width, height): ");        double firstWidth = input.nextDouble();        double firstHeight = input.nextDouble();        System.out.print("Crate the second Rectangle (enter width, height): ");        double secondWidth = input.nextDouble();        double secondHeight = input.nextDouble();        CompareMyRectangle rectangle1 = new CompareMyRectangle(firstWidth, firstHeight);        CompareMyRectangle rectangle2 = new CompareMyRectangle(secondWidth, secondHeight);        System.out.println(CompareGeometricObject.max(rectangle1, rectangle2).toString());        // 可以看出此处的 max 返回的是 CompareMyRectangle 的一个实例    }}