code: private String format(double fileSize, Units units)
    {
      StringBuilder builder = new StringBuilder();
      builder.append(numberFormat.format(fileSize));
      builder.append(' ');
      builder.append(units.name());
      return builder.toString();
    }
docs: Build file size representation for given numeric value and units.
  
  @param fileSize file size numeric part value,
  @param units file size units.
  @return formated file size.