Union Streams in Java

Question

I think this question is useless, but i can`t find how i can union this code to one line

I have List of active Couriers. I am trying to find all free couriers in this list and after that find courier with min distance

List<Courier> afterCheckIsFree = activeCouriers.stream().filter(Courier::isFree).collect(Collectors.toList());
final Optional<Courier> courierWithMinDistance = afterCheckIsFree.stream()
                .filter(n -> n.getId().equals(CourierFinder.minDistanceUsingCourier(Point.ZERO_POINT, afterCheckIsFree).getId())).findFirst();

Thanks a lot!

Answer 1

You should apply 2 criterias on your stream: firstly, checking if courier is free, secondly, sort remaining couriers by distance and take first. It will look like:

list.stream().filter(Courier::isFree).sorted((c1, c2)->c1.getDistance().
                               compareTo(c2.getDistance())).
                               findFirst();

Answer 2

Assuming that the actual aim is to find the courier that is both free and has the minimum distance...

Your code will run the minDistance algorithm for every courier, so it is incredibly inefficient. It can be done in one go:

Optional<Courier> = activeCouriers.stream()
  .filter(Courier::isFree)
  .min((c1, c2) -> c1.getDistanceFrom(ZERO_POINT) - c2.getDistanceFrom(ZERO_POINT));

min can find the minimum thing in the stream based on whatever function you want, which is what is used here.

Answer 3

Change the minDistanceUsingCourier method to return the distance for a single courier (instead of the minimum distance of a list of couriers) then:

final Optional<Courier> courierWithMinDistance = activeCouriers.stream()
  .filter(Courier::isFree)
  .min(comparing(c -> minDistanceUsingCourier(Point.ZERO_POINT, c)));