code: public long getTotalRevenueTimeForTrips (Collection<Trip> trips) {
          TIntList times = new TIntArrayList();
          for (Trip trip : trips) {
              StopTime first;
              StopTime last;
              Spliterator<StopTime> stopTimes = feed.getOrderedStopTimesForTrip(trip.trip_id).spliterator();;
  
              first = StreamSupport.stream(stopTimes, false)
                      .findFirst()
                      .orElse(null);
  
              last = StreamSupport.stream(stopTimes, false)
                      .reduce((a, b) -> b)
                      .orElse(null);
  
              if (last != null && first != null) {
                  // revenue time should not include layovers at termini
                  int time = last.arrival_time - first.departure_time;
  
                  times.add(time);
              }
          }
  
          return times.sum();
      }
docs: Get total revenue time (in seconds) for set of trips.
  @param trips
  @return total revenue time (in seconds)