How to get a List from a HashMap>

Question

I want to extract a List from a Map> (E is a random Class) using stream().

I

Answer 1

You can use Collectors2.flatCollect from Eclipse Collections

List<String> list = 
    map.values().stream().collect(Collectors2.flatCollect(l -> l, ArrayList::new));

You can also adapt the Map and use the Eclipse Collections MutableMap API.

List<String> list = 
    Maps.adapt(map).asLazy().flatCollect(l -> l).toList();

The method flatCollect is equivalent to the method flatMap, except flatCollect takes an Iterable instead of a Stream.

Note: I am a committer for Eclipse Collections.