suggestedPostsFor.java

public Iterable<PostSummary> suggestedPostsFor(ProfileId profileId) {
    Iterable<ProfileId> friendIds = friendsOf(profileId);  // Get the friends of the current user
    Set<Topic> topics = favoriteTopicsOf(profileId);       // Get the favorite topics of the current user
    Stream<PostSummary> friendsPosts = stream(friendIds)   // For each friend
            .flatMap(friendId -> lastPostsOf(friendId))    // * Get their last posts
            .filter(post -> post.isAbout(topics));         // * Keep those whose topic is relevant
    return mostLiked(3, friendsPosts);                     // Rank them by like count
}

private List<PostSummary> mostLiked(int count, Stream<PostSummary> posts) {
    return posts
            .sorted(reverseOrder(comparing(PostSummary::getLikesCount)))
            .limit(count)
            .collect(Collectors.toList());
}