@Override
  public T floor(T e) {
    throw new UnsupportedOperationException(HConstants.NOT_IMPLEMENTED);
  }
A {@link java.util.Set} of {@link Cell}s, where an add will overwrite the entry if already exists
in the set. The call to add returns true if no value in the backing map or false if there was an
entry with same key (though value may be different). implementation is tolerant of concurrent get
and set and won't throw ConcurrentModificationException when iterating.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/CellSet.java