@Override
   public void execute (final char command) {
      switch (command) {
      case UP_MOVE:
         moveUp ();
         break;
      case DOWN_MOVE:
         moveDown ();
         break;
      case LEFT_MOVE:
         moveLeft ();
         break;
      case RIGHT_MOVE:
         moveRight ();
         break;
      case WAIT_MOVE:
         moveWait ();
         break;
      case ABORT_MOVE:
         abort ();
         break;
      default:
         // An illegal move should not be the same as an invalid move
         // (meaning blocked move). No penalty should be given for pressing
         // any other key than the ones recognized by the game.
      }
   }