这个是我刚刚写的，可以直接运行的。应该能够满足你的需求吧。

public class Circle {

private float r;

private final static double PI = Math.PI;

Circle()

{

this.r = 1;

}

Circle(float radius)

{

this.r = radius;

}

private double getPerimeter()

{

return PI*2*r;

}

private double getArea()

{

return PI*r*r;

}

private double getRadius()

{

return r;

}

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

Circle myCircle = new Circle(3);

System.out.println(Radius is +myCircle.getRadius()+ Perimeter is +myCircle.getPerimeter()+ Area is +myCircle.getArea());

}

}