A DESCRIPTION OF THE REQUEST :
There are no MultiSet or MultiMap interface specifications. Using the standard Map/Set interface is a bit clumsy, despite there capability to emulate a Multi-variant (as mentioned in online Map doc). I would be happy if just the MultiMap and MultiSet interfaces were specified since I would be implementating my own. I am less concerned about actual implementations (hash-based,tree-based, sorted,linked), though of course, some might scream if interfaces were published without at least a couple implementations ;-). I suppose an AbstractMultiMap and AbstractMultiSet may appease the masses.


JUSTIFICATION :
Though prior bug reports on MultiMap's and MultiSets have been shot down in the past because they are apparently "rarely" used according to Map documentation and also rarely requested, I find that fairly hard to believe. MultiMap's and MultiSet's happen to make fantastic adapters for relational databases or  customer  oriented databases (like the custom one we use at my company).
Posted Date : 2007-06-08 05:51:25.0

N/A

There isn't a lot of enthusiasm among the maintainers of the Collection framework
to design and implement these interfaces/classes.
I personally can't recall having needed one.
It would be more likely that a popular package developed outside the JDK
would be imported into the JDK after having proved its worth in the real world.
Posted Date : 2007-06-08 06:17:44.0

See bug id 4155149.

All is not lost.  Google has developed a Multiset and a few flavors of Multimaps internally, which have been very popular.  They are now part of our open-source Java collections project; I won't give the link but you should be able to find it on your favorite internet search engine site.  Note that as I write this, a major revision of Multiset is just on the verge of being pushed out.

Google will gladly contribute our Multiset and Multimap interfaces and implementations the JDK; the Multiset being the more likely of the two as it is far, far simpler.