圆类，半径r（double），计算周长，面积，π=3.14

[java]代码库

import java.util.Scanner; 
public class Main {    
       public static void main(String[] args) {      
         Scanner scan = new Scanner(System.in);      
         double r_c1 = scan.nextDouble();      
         double r_c2 = scan.nextDouble();      
         scan.close();      
         Circle c1 = new Circle();      
         c1.setR(r_c1);         
         System.out.println(c1.getArea()); 
         System.out.println(c1.getPerimeter());      
         Circle c2 = new Circle(r_c2);      
         System.out.println(c2.getArea());         
         System.out.println(c2.getPerimeter());    
   } 
} 
class Circle
{
	private double r;
	public Circle(double a)
	{
		r = a;
	}
	public Circle()
	{
		r = 0;
	}
	public void setR(double a)
	{
		r = a;
	}
	public double getPerimeter()
	{
		return 2*3.14*r;
	}
	public double getArea()
	{
		return 3.14*r*r;
	}
}