Development Flash ActionScript

package
{
    import flash.display.Sprite;
    import flash.events.KeyboardEvent;
    public class Main extends Sprite
    {
        private var sprite:Sprite = new Sprite();
        public function Main()
        {
            sprite.graphics.beginFill(0xFF0000, 1);
            sprite.graphics.drawRect(0, 0, 20, 20);
            sprite.graphics.endFill();
            addChild(sprite);
            this.stage.addEventListener(KeyboardEvent.KEY_UP,moveSprite);
        }
        private function moveSprite(keyEvent:KeyboardEvent):void
        {
            switch (keyEvent.keyCode)
            {
                case 37:
                    sprite.x--;
                    break;
                case 38:
                    sprite.y--;
                    break;
                case 39:
                    sprite.x++
                    break;
                case 40:
                    sprite.y++;
                    break;
                default:
                    break;
            }
        }
    }
}