设计一个Circle类，该类有属性radius，表示圆的半径，其默认值为1；getArea()返回该圆的面积。 创建一个名为ComparableCircle的类，它继承自Circle类，并实现Comparable接口，在类中实现compareTo方法，使其根据面积比较两个圆。 编写测试程序求出两个ComparableCircle实例对象的较大者。程序输出如下信息： Cirlce: radius = 7.0 Area: 153.93804002589985 Cirlce: radius = 5.0 Area: 78.53981633974483 c1较大

好的，以下是可供参考的代码实现：

class Circle {
    protected double radius; // 圆的半径

    public Circle() {
        this.radius = 1.0; // 默认半径为1
    }

    public Circle(double radius) {
        this.radius = radius;
    }

    public double getArea() {
        return Math.PI * radius * radius; // 计算圆的面积
    }
}

class ComparableCircle extends Circle implements Comparable<ComparableCircle> {
    public ComparableCircle() {
        super();
    }

    public ComparableCircle(double radius) {
        super(radius);
    }

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

public class Test {
    public static void main(String[] args) {
        ComparableCircle c1 = new ComparableCircle(7.0);
        ComparableCircle c2 = new ComparableCircle(5.0);

        System.out.println("Circle: radius = " + c1.radius + " Area: " + c1.getArea());
        System.out.println("Circle: radius = " + c2.radius + " Area: " + c2.getArea());

        if (c1.compareTo(c2) > 0) {
            System.out.println("c1较大");
        } else if (c1.compareTo(c2) < 0) {
            System.out.println("c2较大");
        } else {
            System.out.println("c1和c2一样大");
        }
    }
}

输出结果：

Circle: radius = 7.0 Area: 153.93804002589985
Circle: radius = 5.0 Area: 78.53981633974483
c1较大