(入边形类0ctagon)编写一个名为0ctagon 的类，它继承自Geometricobject类并实现Comparable 和Coneable 接口。假设八边形八条边的边长都相等。它的面积可以使用下面的公式计算: 面积=(2+4/√2)x边长x 边长 画出包括0ctagon、GeometricObject、Comparable和Cloneable的UML图。编写一个测试程序，创建一个边长值为5的0tagon 对象，然后显示它的面积和周长。使用clone 方法创建一个新对象，并使用 compareTo 方法比较这两个对象。

下面是0ctagon类的代码实现：

public class Octagon extends GeometricObject implements Comparable<Octagon>, Cloneable {
    private double side; // 八边形的边长

    public Octagon(double side) {
        this.side = side;
    }

    public double getSide() {
        return side;
    }

    public void setSide(double side) {
        this.side = side;
    }

    @Override
    public double getArea() {
        return (2 + 4 / Math.sqrt(2)) * side * side;
    }

    @Override
    public double getPerimeter() {
        return 8 * side;
    }

    @Override
    public int compareTo(Octagon o) {
        if (this.getArea() > o.getArea())
            return 1;
        else if (this.getArea() < o.getArea())
            return -1;
        else
            return 0;
    }

    @Override
    public Object clone() {
        try {
            return super.clone();
        } catch (CloneNotSupportedException ex) {
            return null;
        }
    }
}

下面是UML图：

+----------------+
|  GeometricObject  |
+----------------+
|    color:String   |
|        filled:boolean   |
+----------------+
|  GeometricObject()   |
|  GeometricObject(color:String, filled:boolean)   |
|  getColor():String   |
|  setColor(color:String):void   |
|  isFilled():boolean   |
|  setFilled(filled:boolean):void   |
|  getArea():double   |
|  getPerimeter():double   |
+----------------+
        ^
        |
+----------------+
|     Octagon     |
+----------------+
|        side:double   |
+----------------+
|  Octagon(side:double)   |
|  getSide():double   |
|  setSide(side:double):void   |
|  getArea():double   |
|  getPerimeter():double   |
|  compareTo(o:Octagon):int   |
|  clone():Object   |
+----------------+
        ^
        |
+----------------+
|    Comparable<Octagon>   |
+----------------+
|  compareTo(o:Octagon):int   |
+----------------+
        ^
        |
+----------------+
|       Cloneable       |
+----------------+
|  clone():Object   |
+----------------+

下面是测试程序的代码：

public class TestOctagon {
    public static void main(String[] args) {
        Octagon octagon1 = new Octagon(5);
        System.out.println("The area of the octagon is " + octagon1.getArea());
        System.out.println("The perimeter of the octagon is " + octagon1.getPerimeter());

        Octagon octagon2 = (Octagon) octagon1.clone();
        System.out.println("Compare the area of the two octagons: " + octagon1.compareTo(octagon2));
    }
}

运行结果：

The area of the octagon is 120.71067811865476
The perimeter of the octagon is 40.0
Compare the area of the two octagons: 0