public class Circle{
private double r;
public Circle(double r){
this.r =r;
}
public double getLength(){
return 2*Math.PI*r;
}
public double getArea(){
return Math.PI*r*r;
}
}编写程序，试用公式计算圆面积和周长陈天艺1636050045
原文：http://www.cnblogs.com/Archon-Cty/p/7497854.html