用java 1定义接口IShape，该接口有2个方法，方法一（求周长）：double perimeter(),方法二（求面积）：double area();2自行定义圆类（Circle），实现IShape接口；3自行定义矩形类（Rectagle），实现IShape接口

//定义IShape接口
public interface IShape {
    double perimeter(); //求周长方法
    double area(); //求面积方法
}

//圆类实现IShape接口
public class Circle implements IShape {
    private double radius; //圆的半径
    private final double PI = 3.1415926; //π的值

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

    @Override
    public double perimeter() {
        return 2 * PI * radius;
    }

    @Override
    public double area() {
        return PI * radius * radius;
    }
}

//矩形类实现IShape接口
public class Rectangle implements IShape {
    private double width; //矩形的宽
    private double height; //矩形的高

    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }

    @Override
    public double perimeter() {
        return 2 * (width + height);
    }

    @Override
    public double area() {
        return width * height;
    }
}