code: protected JournalInputFile openNextFile() throws JournalException {
          File[] journalFiles =
                  MultiFileJournalHelper
                          .getSortedArrayOfJournalFiles(journalDirectory,
                                                        filenamePrefix);
  
          if (journalFiles.length == 0) {
              return null;
          }
  
          JournalInputFile nextFile = new JournalInputFile(journalFiles[0]);
          recoveryLog.log("Opening journal file: '" + nextFile.getFilename()
                  + "'");
          return nextFile;
      }
docs: Look in the directory for files that match the prefix. If there are none,
  leave with currentFile still null. If we find one, advance into it.