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

Collectors.groupingBy is exactly what you want, it creates a Map from your input collection, creating an Entry using the Function you provide for it's key, and a List of Points with your associated key as it's value.

Map> pointByParentId = chargePoints.stream()
    .collect(Collectors.groupingBy(Point::getParentId));