Hi Thomas, This sounds great. Moving MultiKeyMap to the new package does sound like the way to go ahead. I will start with the implementation of the interface and the MultiValuedHashMap. I should be able to submit a patch with a basic implementation and some test cases by the end of this week. I can then modify and incorporate changes as per your review and suggestions.
Regards Dipanjan On Wed, Feb 26, 2014 at 2:32 PM, Thomas Neidhart <thomas.neidh...@gmail.com>wrote: > Hi Dipanjan, > > I was thinking about a name for the new interface, but I actually like your > proposal of MultiValuedMap. > > For the package, I think we can stick with multimap, and at some point we > could also move the MultiKeyMap there, which would be logical imho. > > The implementation names are also sound. > > Thomas > > > > > On Wed, Feb 26, 2014 at 9:28 AM, Dipanjan Laha <dipanja...@gmail.com> > wrote: > > > Hi Thomas, > > > > It would be great if we can start the discussion on the new interface for > > MultiMap and a new package for the implementations as suggested by you. > > Then I'll be able to put some code together for the same. > > > > IMO we can have > > > > 1. New Interface for MultiMap with the name MultiValuedMap or MultiValMap > > (as MultiValueMap is already the existing implementing class). > > 2. New package for the implementations: > > org.apache.commons.collections.multimap or > > org.apache.commons.collections.multivaluedmap > > 3. Implementation names like : MultiValuedHashMap, MultiValuedTreeMap etc > > > > Please let me know of your thoughts on these. > > > > Regards > > Dipanjan > > > > On Sun, Feb 23, 2014 at 8:36 PM, Dipanjan Laha <dipanja...@gmail.com> > > wrote: > > > > > Hi Thomas, > > > > > > Thanks for your feedback. I created an improvement request in Jira for > > the > > > same (https://issues.apache.org/jira/browse/COLLECTIONS-508 ) as I > > > thought it could be better tracked there. Sorry for the duplication in > > the > > > mail list and Jira. I have also attached a patch in Jira where I have > > > modified the existing MultiMap interface and the MultiValueMap > > > implementation and their test cases. I agree that it would break > backward > > > compatibility and we should go with your suggestion of deprecating the > > > existing ones and design fresh interfaces for the same. The patch is > > just a > > > sample implementation to demonstrate the issue and is far from being > > > complete in terms of documentation and test cases. I am also attaching > > the > > > patch here for your reference. > > > > > > Please go through the patch and also let me know of your thoughts on > how > > > we should proceed with the new interface and package structure. I'll be > > > happy to change and redirect the implementation as per your > suggestion. I > > > am new to Apache Commons, but with some guidance I should not have > issues > > > implementing them to start with. > > > > > > As for MultiTrie, as you mentioned, we can start with it once the new > > > MultiMap has been finalized. > > > > > > Regards > > > Dipanjan > > > > > > > > > > > > > > > On Sun, Feb 23, 2014 at 6:09 PM, Thomas Neidhart < > > > thomas.neidh...@gmail.com> wrote: > > > > > >> On 02/22/2014 02:00 PM, Dipanjan Laha wrote: > > >> > Hello, > > >> > > >> Hi Dipanjan, > > >> > > >> > Recently I had the need of using a MultiMap in one of my projects. I > > >> found > > >> > that commons collection already has a MultiMap interface and an > > >> > implementation. > > >> > > > >> > While using the same, I found that the MultiMap interface has > methods > > >> that > > >> > are not strongly typed even though the interface supports generics. > > For > > >> > example if I have a MultiMap like so > > >> > > > >> > MultiMap<String, User> multiMap = new MultiValueMap<String, User>(); > > >> > > > >> > where User is a custom Class, then the get(key) method would return > > me > > >> an > > >> > Object which I would need to cast to a Collection like so > > >> > > > >> > Collection<User> userCol = (Collection<User>) multiMap.get(key); > > >> > > > >> > I understand that this limitation comes from that fact that the > > MultiMap > > >> > extends IterableMap which in turn extends Map and other interfaces. > > >> Hence > > >> > the MultiMap cannot have a get method which returns a Collection > > >> instead of > > >> > Object as that would mean extending IterableMap with the Generics > set > > >> to be > > >> > <K,Collection<V>>. In that case the put method's signature would > > become > > >> > > > >> > public Collection<V> put(K key, Collection<V> value); > > >> > > > >> > which we do not want.The same problem would arise with other methods > > as > > >> > well, ex: containsValue method. > > >> > > > >> > My proposal is why carry on the signatures of a Map and put it on > > >> MultiMap. > > >> > Where as I do agree that it is a Map after all and has very similar > > >> > implementation and functionality, it is very different at other > > levels. > > >> And > > >> > even though the MultiMap interface supports generics, the methods > are > > >> not > > >> > strongly typed, which defeats the purpose of having generics. So why > > >> can't > > >> > we have a separate set of interfaces for MultiMap which do not > extend > > >> Map. > > >> > That way we can have strongly typed methods on the MultiMap. > > >> > > >> The MultiMap interface as it is right now is flawed, and should have > > >> been cleaned up prior to the 4.0 release imho (and I regretted it > > >> already before your post). > > >> > > >> As you correctly pointed out, the problem comes from the fact that it > > >> extends Map<K, Object> which leads to problems once generics have been > > >> introduced (before it did not matter that much as you had to cast > > >> anyway, as it is also documented in the javadoc). > > >> > > >> One mitigation for this was the introduction of this method to > > >> MultiValueMap, but it is clearly not enough: > > >> > > >> public Collection<V> getCollection(Object key) > > >> > > >> > > >> Unfortunately, it is not easy to fix this now after collections 4.0 > has > > >> been released. We need to keep backwards compatibility, but we could > do > > >> the following: > > >> > > >> * deprecate the existing interfaces/classes: > > >> - MultiMap > > >> - MultiValueMap > > >> > > >> * design a new, clean interface (by not extending Map) > > >> * add new package multimap with concrete implementations for > different > > >> types of maps (right now only hashmaps are supported) > > >> > > >> > Please let me know your thoughts on this. I can submit a patch for > > these > > >> > changes based on your feedback. One more thing, I also am in need > of a > > >> > MultiTrie which is currently not there. I am implementing the same > by > > >> > wrapping PatriciaTrie. Now I am a bit confused here as, if I make > the > > >> > MultiTrie interface on the lines of MultiMap, it would have the same > > >> > limitations. In that case I was planning to have a separate set of > > >> > interfaces for MultiTrie which does not extend any other interface. > > And > > >> in > > >> > case, we do change the MultiMap interface to be independent of Map, > > then > > >> > MultiTrie can extend MultiMap. Please let me know your thoughts on > > this > > >> as > > >> > well as I am implementing the same for my project right now and > would > > >> like > > >> > to contribute it back to the commons collection. > > >> > > >> Patches are always welcome, but we first need a decision in which > > >> direction to go, see above. > > >> > > >> Regarding the MultiTrie: > > >> > > >> Indeed, it is the same problem, so it should go hand in hand with the > > >> revamp of the MultiMap interface. > > >> > > >> Thomas > > >> > > >> --------------------------------------------------------------------- > > >> To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > > >> For additional commands, e-mail: dev-h...@commons.apache.org > > >> > > >> > > > > > >
