Java——求图形面积和周长

设计接口图形Shape、及其实现类Circle和Rectangle、工具类Show中提供两个方法showArea和showPerimeter，分别用于显示图形的周长和面积。App类中main方法中给出测试代码。Circle类中无参构造方法将半径赋值为1，Rectangle类中无参构造方法中width和length都赋值为1。如下图：

 

 

 

【输入形式】1或2或3，分别执行不同的代码块，得到不同结果。

import  java.util.Scanner;
//定义接口Shape

interface Shape{
double area();
double perimeter();
}

//定义Circle类

class Circle implements Shape
{
private int r;
public Circle(int r)
{this.r=r;
}
public Circle()
{this.r=1;
}
public double area()
{return r*r*3.141592653589793;}
public double perimeter()
{return 2*3.141592653589793*r;}
}

//定义Rectangle类

class Rectangle implements Shape
{
private int w;
private int l;
public Rectangle(int w,int l)
{this.w=w;
this.l=l;
}

public Rectangle()
{this.w=1;
this.l=1;
}
public double area()
{return w*l;}
public double perimeter()
{return 2*(w+l);}
}

class  Show  {
   static void showArea (Shape s)

{ System.out.println(s.area());}
static void showPerimeter (Shape s)
{System.out.println(s.perimeter());}

}

public  class  App  {
        public  static  void  main(String[]  args)  {
                int  n;
                Scanner  scan=new  Scanner(System.in);
                n=scan.nextInt();
                Shape  s;
                switch(n){
                case  1:
                        s=new  Circle();
                        Show.showArea(s);
                        Show.showPerimeter(s);
                        break;
                case  2:
                        s=new  Circle(2);
                        Show.showArea(s);
                        Show.showPerimeter(s);
                        break;
                case  3:
                        s=new  Rectangle(2,  6);
                        Show.showArea(s);
                        Show.showPerimeter(s);
                        break;
                case  4:
                        s=new  Rectangle();
                        Show.showArea(s);
                        Show.showPerimeter(s);
                }
                scan.close();
        }
}