Java 8 Distinct by property

Question

In Java 8 how can I filter a collection using the Stream API by checking the distinctness of a property of each object?

For example I have a list of

Answer 1

Late to the party but I sometimes use this one-liner as an equivalent:

((Function) Value::getKey).andThen(new HashSet<>()::add)::apply

The expression is a Predicate but since the map is inline, it works as a filter. This is of course less readable but sometimes it can be helpful to avoid the method.