code: public static String nameFromOffset(long offset) {
          NumberFormat nf = NumberFormat.getInstance();
          nf.setMinimumIntegerDigits(20);
          nf.setMaximumFractionDigits(0);
          nf.setGroupingUsed(false);
          return nf.format(offset) + Log.FileSuffix;
      }
docs: Make log segment file name from offset bytes. All this does is pad out the offset number
  with zeros so that ls sorts the files numerically
  @param offset offset value (padding with zero)
  @return filename with offset