How can i run this code correctly?

Question

hello, everybody:
    when  i run the code, i found that it dons't work,so ,i  hope somebody can help me!
    the Ball class is this :
    package {
    import flash.display.Sprite;
    [SWF(width = "550", height = "400")]
    public class Ball extends Sprite {
        private var radius:Number;
        private var color:uint;
        private var vx:Number;
        private var vy:Number;
        public function Ball(radius:Number=40, color:uint=0xff9900,
        vx:Number =0, vy:Number =0) {
            this.radius= radius;
            this.color = color;
            this.vx = vx;
            this.vy = vy;
            init();
        private function init():void {
            graphics.beginFill(color);
            graphics.drawCircle(0,0,radius);
            graphics.endFill();
and the Chain class code is :
package {
    import flash.display.Sprite;
    import flash.events.Event;
    [SWF(width = "550", height = "400")]
    public class Chain extends Sprite {
        private var ball0:Ball;
        private var ball1:Ball;
        private var ball2:Ball;
        private var spring:Number = 0.1;
        private var friction:Number = 0.8;
        private var gravity:Number = 5;
        //private var vx:Number =0;
        //private var vy:Number = 0;
        public function Chain() {
            init();
        public function init():void {
            ball0  = new Ball(20);
            addChild(ball0);
            ball1 = new Ball(20);
            addChild(ball1);
            ball2 = new Ball(20);
            addChild(ball2);
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
        private function onEnterFrame(event:Event):void {
            moveBall(ball0, mouseX, mouseY);
            moveBall(ball1, ball0.x, ball0.y);
            moveBall(ball2, ball1.x, ball1.y);
            graphics.clear();
            graphics.lineStyle(1);
            graphics.moveTo(mouseX, mouseY);
            graphics.lineTo(ball0.x, ball0.y);
            graphics.lineTo(ball1.x, ball1.y);
            graphics.lineTo(ball2.x, ball2.y);
        private function moveBall(ball:Ball,
                                  targetX:Number,
                                  targetY:Number):void {
            ball.vx += (targetX - ball.x) * spring;
            ball.vy += (targetY - ball.y) * spring;
            ball.vy += gravity;
            ball.vx *= friction;
            ball.vy *= friction;
            ball.x += vx;
            ball.y += vy;
thanks every body's help!

Answer 1

ok, thanks for your reply ! I run this code in the Flex builder 3!and the Ball class and the Chain class are all in the same AS project!
  and i changed the ball.pv property as public in the Ball class, and  the Chain class has no wrong syntactic analysis,but the AS code don't run.so this is the problem.
2010-04-21
Fang
发件人: Ned Murphy <[email protected]>
发送时间: 2010-04-20 23:01
主 题: how  can i run this code correctly?
收件人: fang alvin <[email protected]>
I don't see that the Ball class has a pv property, or that you even try to access a pv property in the Chain class.  All of the properties in your Ball class are declared as private, so you probably cannot access them directly.  They would need to be public.  Also, I still don't see where you import Ball in the chain class such that it can use it.