public static boolean isValid(int x, int y)
   {
      Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
      double width = screenSize.getWidth();
      double height = screenSize.getHeight();

      if(x >= (width / 2) && x <= width && y >= (height / 2) && y <= height)
      {
         return true;
      }
      else
      {
         System.out.println("---------INVALID COORDINATES------------");
         System.out.printf("(%d,%d) exceed the maximum screen size%n", x, y);
         System.out.println("----------------------------------------");
      }
      return false;
   }