Question

I’m looking for an implementation of java.util.Map that has a method that will return all they keys mapped to a given value, that is, there are multiple keys map to the same value. I’ve looked at Google Collections and Apache Commons and didn’t notice anything. Of course, I could iterate through the keyset and check each corresponding value or use two maps, but I was hoping there was something available already built.

Answer 1

I don’t know if that solution is good for you, but you can implement easily that by using a standard map from keys to values and a MultiMap from values to key.

Of course you’ll have to take care of the syncronization of the two structures, IE when you remove a key from the map, you have to remove the key itself from the set of keys mapped to the value in the multimap.

It doesn’t seems difficult to implement, maybe a bit heavy from the memory overhead aspect.