@Override
 public void moveLeft() {
   center.x -= center.xSpeed;
 }
 @Override
 public void moveDown() {
   center.y += center.ySpeed;
 }
 @Override
 public void moveRight() {
   center.x += center.xSpeed;
 }
 @Override
 public void moveUp() {
   center.y -= center.ySpeed;
 }