Java: count the total number of items in a HashMap<String, ArrayList<String>>

Question

I have this HashMap<String, ArrayList<Item>> , is there a way to count the total number of items in all the Lists in the Map without going through all Lists?

Or should I iterate through the Map and along all lists ?

Answer 1

As of Java 8 you accomplish that with an one-liner:

Integer sum = map.values().stream().mapToInt(List::size).sum();