public synchronized void printBoard()
    {
        System.out.println();
        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[i].length; j++) {
                if (board[i][j] == null) {
                    System.out.print("_");
                } else {
                    System.out.print(board[i][j]);
                }
                if (j < 2) {
                    System.out.print("|");
                } else {
                    System.out.println();
                } 
             }
         }
         System.out.println("\n");
    }