求教高手一个JAVA的小问题

在Circle类中增加public void setR(int r){this.r = r;}
Testcircle类的main方法改成：
public static void main(String[] args)
{
Circle circle = new Circle();
java.util.Scanner input = new java.util.Scanner(System.in);
System.out.println("请输入半径：");
circle.setR(input.nextInt());
System.out.println("圆的面积是："+circle.ca);
System.out.println("圆的周长是："+circle.cc);
circle.clear();
}

import static java.lang.Math.*;
class Circle
{
private double circumference;
private double area;

public double cc(int r)
{
circumference=2*PI*r;
return circumference;
}
public double ca(int r)
{
area=PI*r*r;
return area;
}
public void clear()
{
r=0;
}
}

class Testcircle
{
public static void main(String[] args)
{
Circle circle = new Circle();
java.util.Scanner input = new java.util.Scanner(System.in);
System.out.println("请输入半径：");
int r=input.nextInt();
System.out.println("圆的面积是："+circle.ca(r));
System.out.println("圆的周长是："+circle.cc(r));
circle.clear();

}
}

你应该吧ca（）和cc（）方法的参数设置成你输入的数，不然JVM不知道拿你输入的r来干嘛...