Java parallel stream: how to wait for threads for a parallel stream to finish?

Question

So I have a list from which I obtain a parallel stream to fill out a map, as follows:

Map map = new HashMap<>();
List

        

Answer 1

Stream operations will block until done for both - parallel and not parallel implementations.

So what you see is not the "putting data" process is still going on - most likely it's just data corruption, since HashMap is not threadsafe. Try using ConcurrentHashMap instead.