Lambda in Stream.map/filter not called

Question

I\'m trying to find separate the duplicates and non-duplicates in a List by adding them to a Set and List while using Stream.fil

Answer 1

In order to the filter to be applied, you need to call a terminal operation like collect(). In that case you can assign the items which pass the filter directly to the extras list instead of use map function.

Try something like this:

List strings = Arrays.asList("foo", "bar", "foo", "baz", "foo", "bar");

Set distinct = new HashSet<>();

List extras = strings
                     .stream()
                     .filter(x -> !distinct.add(x))
                     .collect(Collectors.toList());