@Override
    public int compare(final RegionState l, final RegionState r) {
      int stampCmp = Long.compare(l.getStamp(), r.getStamp());
      return stampCmp != 0 ? stampCmp : RegionInfo.COMPARATOR.compare(l.getRegion(), r.getRegion());
    }
RegionStates contains a set of Maps that describes the in-memory state of the AM, with the
regions available in the system, the region in transition, the offline regions and the servers
holding regions.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionStates.java