java多态与接口的题

希望各位指点一二！

↑这是题目

package jiekou;
interface Shape{
    double getArea();
    double getPerimeter();
    void drawing();
}
class Rectangle implements Shape
{
    private double length;
    private double width;
    public Rectangle(double length, double width) {
        super();
        this.length = length;
        this.width = width;
    }
    @Override
    public String toString() {
        return " 长为" + length + ", 宽为" + width ;
    }
    public double getArea()
    {
        return length*width;
    }
    public double getPerimeter()
    {
        return 2*(length+width);
    }
    public void drawing()
    {
        System.out.println("正在绘制一个长方形"+toString());
    }
}
class Circle implements Shape
{
    private double radius;

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

    @Override
    public String toString() {
        return "半径为" + radius ;
    }
    public double getArea()
    {
        return Math.PI*radius*radius;
    }
    public double getPerimeter()
    {
        return 2*Math.PI*radius;
    }
    public void drawing()
    {
        System.out.println("正在绘制一个圆"+toString());
    }
}

以上是我已经完成的代码，MyShape类的建立和之后测试类的调用我就不是很会用了

希望得到各位指点

Circle类的radius加上getter方法

MyShape

class MyShape {
    public static void area(Shape shape) {
        if (shape instanceof Circle) {
            System.out.println("半径为" + ((Circle) shape).getRadius() + "圆面积：");
        } else {
            System.out.println("指定长宽的矩形面积：");
        }
        System.out.println(shape.getArea());
    }

    public static void perimeter(Shape shape) {
        if (shape instanceof Circle) {
            System.out.println("半径为" + ((Circle) shape).getRadius() + "圆周长：");
        } else {
            System.out.println("指定长宽的矩形周长：");
        }
        System.out.println(shape.getPerimeter());
    }

    public static void drawing(Shape shape) {
        shape.drawing();
    }
}

测试代码

public class TestShape {
    public static void main(String[] args) {
        Circle circle = new Circle(10);
        MyShape.area(circle);
        MyShape.perimeter(circle);
        MyShape.drawing(circle);

        Rectangle rectangle = new Rectangle(10, 20);
        MyShape.area(rectangle);
        MyShape.perimeter(rectangle);
        MyShape.drawing(rectangle);
    }
}