Options to accumulate from a List without an intermediate

[Arul Dhesiaseelan]

Is there a better way to accumulate tracks from an album, without using an
intermediate?

Take1 uses an intermediate, while Take2 does not use one, but more verbose.
May be there is a better way?

Take#1
    final List<Track> tracks = new ArrayList<>();
    albums.stream().forEach(album -> tracks.addAll(album.tracks));

    // Group album tracks by rating
    Map<Integer, Collection<Track>> tracksByRating =
tracks.stream().accumulate(Accumulators.<Track,
Integer>groupBy(Track::getRating));

Take#2
    Map<Integer, Collection<Track>> tracksByRating =
albums.stream().accumulate(new Accumulator<Album, List<Track>>() {
      @Override
      public List<Track> makeResult() {
        return new ArrayList<>();
      }

      @Override
      public void accumulate(List<Track> result, Album value) {
        result.addAll(value.tracks);
      }

      @Override
      public List<Track> combine(List<Track> result, List<Track> other) {
        return Streams.concat(result.stream(), other.stream()).into(new
ArrayList<Track>());
      }
    }).stream().accumulate(Accumulators.<Track,
Integer>groupBy(Track::getRating));


Thanks!
Arul