[FIXED] Accumulate values and return result in Java stream

Issue

I have a class with a collection of Seed elements. One of the method's return type of Seed is Optional<Pair<Boolean, Boolean>>.

I'm trying to loop over all seeds, keeping the return type (Optional<Pair<Boolean, Boolean>>), but I would like to be able to say if there was at least true value (in any of the Pairs) and override the result with it. Basically, if the collection is (skipping the Optional wrapper to make things simpler): [Pair<false, false>, Pair<false, true>, Pair<false, false>] I would like to return and Optional of Pair<false, true> because the second element had true. In the end, I'm interested if there was a true value and that's about it.

  public Optional<Pair<Boolean, Boolean>> hadAnyExposure() {
    return seeds.stream()
        .map(Seed::hadExposure)
        ...
  }

I was playing with reduce but couldn't come up with anything useful.

My question is related with Java streams directly. I can easily do this with a for loop, but I aimed initially for streams.

Solution

Your thoughts on reduce look like the right way to go, using || to reduce both sides of each Pair together. (Not exactly sure what your Optional semantics are, so going to filter out empty ones here and that might get what you want, but you may need to adjust):

Optional<Pair<Boolean, Boolean>> result = seeds.stream().map(Seed::hadExposure)
                .filter(Optional::isPresent)
                .map(Optional::get)
                .reduce((a, b) -> new Pair<>(a.first || b.first, a.second || b.second));

Answered By - Joe
Answer Checked By - Cary Denson (JavaFixing Admin)