code: public static String getCellAddressA1Format(int rowNum, int columnNum) {
   CellAddress cellAddr = new CellAddress(rowNum, columnNum);
   return cellAddr.formatAsString();
  }
docs: Generate a cell address in A1 format from a row and column number
  
  @param rowNum row number
  @param columnNum column number
  
  @return Address in A1 format