code: @Override
      public String[] getSheetNames()
      {
          String[] ret = null;
          if(sheets != null)
          {
              ret = new String[sheets.size()];
              for(int i = 0; i < sheets.size(); i++)
              {
                  Sheet sheet = (Sheet)sheets.get(i);
                  ret[i] = sheet.getName();
              }
          }
          return ret;
      }
docs: Returns the list of worksheet names from the given Excel XLSX file.
  @return The list of worksheet names from the given workbook