Convert List<Object> to Map<Integer, List<Object>> using Java 8 Streams API

Question

I have List<Object> , and I want to convert it into Map<Integer, List<Object>> where key is the size of the list and value is the list itself using java 8 streams api. I can do it using Java 7 as

Map<Integer, List<Object>> map= new HashMap<>();
map.put(list.size(), list);

But how to do it using Java 8.

Answer 1

That should be just

Stream.of(list)
    .collect(Collectors.toMap(List::size, Function.identity()));

---

But why do you want to do this? It's pointless. If you had written this and I were to review your code, I would definitely reject this.

The Streams API is not some magical key to just solve everything. The Streams API is built to operate on streams of elements , in a functional manner.

Just stick with the way you mentioned in your post.