@Override
    public int hashCode() {
      final int prime = 31;
      int result = 1;
      result = prime * result + ((newestOffset == null) ? 0 : newestOffset.hashCode());
      result = prime * result + ((oldestOffset == null) ? 0 : oldestOffset.hashCode());
      result = prime * result + ((upcomingOffset == null) ? 0 : upcomingOffset.hashCode());
      return result;
    }
@param offsetType
         The type of offset to get. Either oldest, newest, or upcoming.
@return The corresponding offset for the offset type requested.
samza-api/src/main/java/org/apache/samza/system/SystemStreamMetadata.java