function moveLeft():Void {
    var leftWall:Number = 0;
    if(target._x > leftWall) {
      target._x -= SPEED;
    }else {
      target._x = leftWall;
    }
  }
  function moveRight():Void {
    var rightWall:Number = Stage.width - target._width;
    if(target._x < rightWall) {
      target._x += SPEED;
    }else {
      target._x = rightWall;
    }
   }
  function moveUp():Void {
    var topWall:Number = 0
    if(target._y > topWall) {
      target._y -= SPEED;
    }else {
      target._y = topWall;
    }
  }
  function moveDown():Void {
    var bottomWall:Number = Stage.height - target._height;
    if(target._y < bottomWall) {
      target._y += SPEED;
    }else {
      target._y = bottomWall;
    }
  }