suggestedPostsFor.java

public Iterable<PostSummary> suggestedPostsFor(ProfileId profileId) {
    Iterable<ProfileId> friendIds = friendsOf(profileId);
    Set<Topic> topics = favoriteTopicsOf(profileId);
    Stream<PostSummary> interestingPosts = stream(friendIds)
            .flatMap(friendId -> lastPostsOf(friendId))
            .filter(post -> post.isAbout(topics));
    return mostLiked(3, interestingPosts);
}