オブジェクトの移動と削除

/**
 * Copyright _wonder ( http://wonderfl.net/user/_wonder )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/6HiS
 */

package {
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.events.Event;
    
    public class Removal extends Sprite {
    		private var count:int = 20;
    		private var balls:Array;
    		
    		public function Removal() {
            init();            
        }
        
        private function init():void {
        		stage.scaleMode = StageScaleMode.NO_SCALE;
        		stage.align = StageAlign.TOP_LEFT;
        		
        		balls = new Array();
        		for( var i:int = 0; i < count; i++ ){
        			var ball:Ball = new Ball( 10 );
        			ball.x = Math.random() * stage.stageWidth;
        			ball.y = Math.random() * stage.stageHeight;
        			ball.vx = Math.random() * 2-1;
        			ball.vy = Math.random() * 2-1;
        			addChild( ball );
        			balls.push( ball );
        		}
        		addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }
        
        private function onEnterFrame( e:Event ):void {
        		for( var i:Number = 0; i < balls.length; i++ ){
        			var ball:Ball = Ball(balls[i]);
        			ball.x += ball.vx;
        			ball.y += ball.vy;
        			if( ball.x - ball.radius > stage.stageWidth || 
        				ball.x + ball.radius < 0 ||
        				ball.y - ball.radius > stage.stageHeight ||
        				ball.y + ball.radius < 0){
        					removeChild( ball );
        					balls.splice( i , 1);
        					if(balls.length <= 0){
        						removeEventListener(Event.ENTER_FRAME, onEnterFrame);
        					}
        			}
        		}
        }
    }
}

import flash.display.Sprite;

class Ball extends Sprite {
	public var radius:Number;
	public var color:uint;
	public var vx:Number = 0;
	public var vy:Number = 0;
	
	public function Ball(radius:Number=40, color:uint=0xff0000){
		this.radius = radius;
		this.color = color;
		init();
	}
	
	public function init():void {
		graphics.beginFill( color );
		graphics.drawCircle(0,0,radius);
		graphics.endFill();
	}
}