[FIXED] Converting an Optional to a List

Issue

I want to collect an Optional into a List, so that I end up with a list with a single element, if the optional is present or an empty list if not.

They only way I came up with (in Java 11) is going through a Stream:

var maybe = Optional.of("Maybe");
var list = maybe.stream().collect(Collectors.toList());

I know, this should be rather efficient anyway, but I was wondering, if there is an easier way to convert the Optional into a List without using an intermediate Stream?

Solution

I think that the most idiomatic way would be to use Optional.map:

var maybe = Optional.of("Maybe");
var list = maybe.map(List::of).orElse(Collections.emptyList());

Or, if you don't want to create an empty list that might end up being not used at the end:

var list = maybe.map(List::of).orElseGet(Collections::emptyList);

Answered By - fps
Answer Checked By - Marilyn (JavaFixing Volunteer)