Development Flash ActionScript

package {
     
     import flash.display.Sprite;
     import flash.events.MouseEvent;
     
     [SWF(width=550, height=400)]
     public class Main extends Sprite {
     
          private static var UP_COLOR:uint = 0xFF0000;
          private static var ROLLOVER_COLOR:uint = 0x0000FF;
          
          private var _square:Sprite = new Sprite();
          
          public function Main() {
               drawSquare(UP_COLOR);
               addChild(_square);
               
               _square.doubleClickEnabled = true;
               
               _square.addEventListener(MouseEvent.CLICK, onSquareClick);
               _square.addEventListener(MouseEvent.DOUBLE_CLICK, onSquareDoubleClick);
               _square.addEventListener(MouseEvent.ROLL_OVER, onSquareRollOver);
               _square.addEventListener(MouseEvent.ROLL_OUT, onSquareRollOut); 
          }
          
          private function drawSquare(color:uint):void {
               _square.graphics.clear();
               _square.graphics.lineStyle(2, 0x000000);
               _square.graphics.beginFill(color);
               _square.graphics.drawRect(0, 0, 100, 100);
               _square.graphics.endFill();
          }
          
          private function onSquareClick(event:MouseEvent):void {
               trace("ouch!");
          }
          
          private function onSquareDoubleClick(event:MouseEvent):void {
               trace("double ouch!");
          }
          
          private function onSquareRollOver(event:MouseEvent):void {
               drawSquare(ROLLOVER_COLOR);
          }
          
          private function onSquareRollOut(event:MouseEvent):void {
               drawSquare(UP_COLOR);
          }
     }
}