带比较器的有序流

Question

Does getSortedUsers() always returns an orderd stream of getUsers() independent of the getUsers() -collection type?

public Set<User> getUsers(){
    // unordered collection type
    HashSet<User> set = new HashSet<>();
    set.add(..);
    set.add(..);
    set.add(..);
    return set;
}

// Is the stream only sorted if getUsers() is hold within a sortable collection type?
public Stream<User> getSortedUsers(Comparator<User> comp){
    return getUsers().stream().sorted(comp);
}

Answer 1

The Stream returned by getSortedUsers() will always be sorted, which is guaranteed by the call to sorted(comp) . It doesn't matter what's the source of the Stream .

Now, if you decide to collect the elements of that Stream into some Collection , the order may or may not be preserved, depending on which type of Collection you choose. If you collect the elements into a HashSet , you'll lose the order. If you collect into a TreeSet , a LinkedHashSet or any List , you'll keep the order.