How to convert an Optional into a Stream?

Question

I want to prepend a stream with an Optional. Since Stream.concat can only concatinate Streams I have this question:

How do I convert an Optional

Answer 1

If you're on an older version of Java (lookin' at you, Android) and are using the aNNiMON Lightweight Stream API, you can do something along the lines of the following:

    final List flintstones = new ArrayList(){{
        add("Fred");
        add("Wilma");
        add("Pebbles");
    }};

    final List another = Optional.ofNullable(flintstones)
            .map(Stream::of)
            .orElseGet(Stream::empty)
            .toList();

This example just makes a copy of the list.