Multimap with HashMultiset for values

Question

Hi,

I'm trying to have a (hash-based) Multimap with a (hash-based) Multiset of values for each key. See the example:

Multimap<Object, Object> mmap = Multimaps.newMultimap(
    Maps.<Object, Collection<Object>>newHashMap(), 
    new Supplier<Collection<Object>>() {
  public Collection<Object> get() {
    return HashMultiset.create();
  }
});
mmap.put("1", "2");

But then,

System.out.println(mmap.get("1") instanceof Multiset<?>); 
//false, the returned collection is not a HashMultiset,
//but a (private) WrappedCollection

So it seems I cannot access the multiset I created? I wanted to be able to return that, as a Multiset (wrapped in Multisets.unmodifiableMultiset()). I don't want to copy it into a new Multiset each time either. Do I have any other option than switching back to Map<K, Multiset<V>> and adding in my code the complexity that Multimap meant to eliminate?

Answer 1

The Multimap interface only specifies that get(K) return a Collection<V>. I think it would be poor design for your code to depend or assume anything else.

Can you expand a little bit more on what you are trying to do here? Seems like there should be an easier way to accomplish it.

Answer 2

I'm afraid this doesn't seem to be possible. You should file a feature request. I have a sneaking suspicion those crafty Google folks have a nifty kind of a Multimap that they could potentially release that might potentially help you.