Keyboard Listening Problem

programming flash
1

I have a ship on stage but I can’t move the ship with keyboard

package {
	
	import flash.display.MovieClip;
	import flash.events.Event;
	import flash.events.KeyboardEvent;
	import flash.ui.Keyboard;
	
	public class Ship extends MovieClip {
		
		public var shipSpeed:uint = 3;
		
		public function Ship () {
		
		  addEventListener(Event.ENTER_FRAME,shipEnterFrame);
		}
		private function shipEnterFrame(event:Event):void {
		 
                 addEventListener(KeyboardEvent.KEY_DOWN,gameKeyDown);
		}
		private function gameKeyDown(event:KeyboardEvent):void {
			switch(event.keyCode) {
				case Keyboard.UP : 
				y -= shipSpeed;
				break;
				case Keyboard.DOWN :
				y += shipSpeed;
				break;
				case Keyboard.RIGHT :
				x += shipSpeed;
				break;
				case Keyboard.LEFT :
				x -= shipSpeed;
				break;
				case Keyboard.SPACE :
				Fire();
				break;
			}
		}
		public function Fire () {
			var missile:Missile = new Missile();
			missile.x = x + 50;
			missile.y = y + 2 ;
			addChildAt(missile,numChildren - 1);
		}
	}
}