题目求源码，不太会写，求源码⋯⋯

Question

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Answer 1

仅供参考

public class ShapeTest {

    abstract class Shape{
        public abstract double area();
        public abstract double perimeter();
    }

    class Rect extends Shape{

        private double width;
        private double length;

        public Rect(double w,double l){
            width = w;
            length = l;
        }
        @Override
        public double area() {
            return width*length;
        }

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

    class Circle extends Shape{

        private double r;
        public Circle(double r){
            this.r = r;
        }
        @Override
        public double area() {
            return Math.PI * r * r;
        }

        @Override
        public double perimeter() {
            return 2 * Math.PI * r;
        }
    }
    public static void main(String[] args){

        ShapeTest st = new ShapeTest();

        Rect r = st.new Rect(2,3);
        System.out.println("矩形的周长为："+r.perimeter());
        System.out.println("矩形的面积为："+r.area());

        Circle c = st.new Circle(1); //单位圆
        System.out.println("圆形的周长为："+c.perimeter());
        System.out.println("圆形的面积为："+c.area());
    }
}