Multimap with HashMultiset for values

Question

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?

score 6 · Accepted Answer · answered Jan 22 '10 at 23:06

6

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.

answered Jan 22 '10 at 23:06

Kevin Bourrillion

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Oh well, that's what I suspected, thanks anyway. I'm not exactly sure what feature to ask for (since there is always the danger of getting it :)). PS: you are so secretive at times! – Dimitris Andreou Jan 23 '10 at 00:42
2

I'd like this too. No chance it's happened in the last ≳4 years? – Matt Ball Jul 11 '14 at 19:00
1

Alas, no, we have lost faith in the particular solution we formerly thought we might release. – Kevin Bourrillion Nov 02 '14 at 16:42

score 0 · Answer 2 · answered Jan 22 '10 at 18:28

0

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.

answered Jan 22 '10 at 18:28

matt b

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The short version of the question is: "I just want a multimap where I can see the values through the Multiset API, not the Collection API". – Dimitris Andreou Jan 22 '10 at 18:55

Multimap with HashMultiset for values

2 Answers2