Shape.class

package com.imooc;
public abstract class Shape 
{
    abstract void circumference(); //周长
        abstract void area();      //面积
}

Rectangle.class

package com.imooc;

import java.util.Scanner;

public class Rectangle extends Shape 
{
    Scanner input=new Scanner(System.in);
    int length=input.nextInt();
    int width=input.nextInt();
    @Override
    void circumference() 
    {
        System.out.println("矩形的周长是"+2*(length+width));
    }
    @Override
    void area() 
    {
        System.out.println("矩形的面积是"+length*width);
    }
}

Circular.java

package com.imooc;

import java.util.Scanner;

public class Circular extends Shape 
{
    static double PI=3.14;
    Scanner input=new Scanner(System.in);
    int r=input.nextInt();
    @Override
    void circumference() 
    {
        System.out.println("圆的周长是"+2*PI*r);
    }

    @Override
    void area() 
    {
        System.out.println("圆的面积是"+PI*r*r);
    }
}

Test.java

package com.imooc;

public class Test
{
    public static void main(String[] args) 
    {
        System.out.println("请输入矩形的长和宽");
        Shape rec=new Rectangle();
        rec.circumference();
        rec.area();
        System.out.println("请输入圆的半径");
        Shape cir=new Circular();
        cir.circumference();
        cir.area();
    }
}

运行结果

请输入矩形的长和宽
7 8
矩形的周长是30
矩形的面积是56
请输入圆的半径
4
圆的周长是25.12
圆的面积是50.24