code: public void combine(WSStatistic otherStat) {
          if (!validate(otherStat))
              return;
  
          DoubleStatisticImpl other = (DoubleStatisticImpl) otherStat;
          count += other.count;
          //TODO: how to update lastSampleTime???
          //if (other.lastSampleTime > lastSampleTime)
          //  lastSampleTime = other.lastSampleTime;
      }
docs: combine the value of this data and other data