package {
   
    public class Controller extends Sprite {

        private static var _instance:Controller;
        private static var _allowInstantiation:Boolean;

        public static function getInstance():Controller {
            if(_instance == null) {
                _allowInstantiation = true;
                _instance = new Controller();
                _allowInstantiation = false;
            }
            return _instance;
        }

        public function Controller():void {
            if(!_allowInstantiation) {
                throw new Error("Error: Instantiation failed: Use Controller.getInstance() instead of new.");
            } else {

                // Place all your code that you want to be hit only once here!

            }
        }
    }
}