Differences between Collectors.toMap() and Collectors.groupingBy() to collect into a Map

Question

I want to create a Map from a List of Points and have inside the map all entries from the list mapped with the same parentId such as

Answer 1

The following code does the stuff. Collectors.toList() is the default one, so you can skip it, but in case you want to have Map> Collectors.toSet() would be needed.

Map> map = pointList.stream()
                .collect(Collectors.groupingBy(Point::getParentId, Collectors.toList()));