java - How to add element into ArrayList in HashMap

Question

How to add element into ArrayList in HashMap?

    HashMap<String, ArrayList<Item>> Items = new HashMap<String, ArrayList<Item>>();

Answer 1

I know, this is an old question. But just for the sake of completeness, the lambda version.

Map<String, List<Item>> items = new HashMap<>();
items.computeIfAbsent(key, k -> new ArrayList<>()).add(item);