import java.lang.Math;
public class C{ private double radius; C(double r){ this.radius = r; } public double areaCal(){ return Math.PI*this.radius*this.radius; } public double perimeterCal(){ return 2*Math.PI*this.radius; } public static void main(String[] args){ c = new C(); System.out.println("周长为："+c.perimeterCal()); System.out.println("面积为: "+c.areaCal()); }}原文：http://www.cnblogs.com/woof95610/p/7504399.html