private String translatePos(int row, int col) {
      if (row < RowNum && col < ColNum && row >= 0 && col >= 0) {
         // if the row and column number is valid for our grid
         StringBuilder str = new StringBuilder();
         str.append("");
         if (reverse) {
            str.append((char)('E' - col));
         }
         else {
            str.append((char)('A' + col));
         }
        
         // here the row will only smaller than 6
         str.append((char)('1' + row));
         return str.toString();
      }
      else {
         if (DEBUG) {
            System.out.println("row = " + row);
            System.out.println("col = " + col);
         }
         throw new RuntimeException("Position invalid!\n");
      }
   }