code: public XceliteSheet getSheet(int sheetIndex) {
      Sheet sheet = workbook.getSheetAt(sheetIndex);
      if (sheet == null) {
        throw new XceliteException(String.format("Could not find sheet at index %s", sheetIndex));
      }
      return new XceliteSheetImpl(sheet, file);
    }
docs: Gets the sheet at the specified index.
  
  @param sheetIndex the sheet index
  @return XceliteSheet object