docs: public static boolean isSegmentFile(String journalName, String fileName) {
      checkNotNull(journalName, "journalName cannot be null");
      checkNotNull(fileName, "fileName cannot be null");
  
      int partSeparator = fileName.lastIndexOf(PART_SEPARATOR);
      int extensionSeparator = fileName.lastIndexOf(EXTENSION_SEPARATOR);
  
      if (extensionSeparator == -1
          || partSeparator == -1
          || extensionSeparator < partSeparator
          || !fileName.endsWith(EXTENSION)) {
        return false;
      }
  
      for (int i = partSeparator + 1; i < extensionSeparator; i++) {
        if (!Character.isDigit(fileName.charAt(i))) {
          return false;
        }
      }
  
      return fileName.startsWith(journalName);
    }