@Override
    public int compare(FileInfo o1, FileInfo o2) {
      if (o1 == null || o2 == null) {
        throw new NullPointerException("arguments to compare two files is null");
      }
      Offset o1Offset = IndexSegment.getIndexSegmentStartOffset(o1.getFileName());
      return o1Offset.compareTo(IndexSegment.getIndexSegmentStartOffset(o2.getFileName()));
    }
Represents the different types of index entries.
ambry-store/src/main/java/com/github/ambry/store/PersistentIndex.java