Map implementation with duplicate keys
duplicates, guava, java, multimap
Solution
You are searching for a multimap, and indeed both commons-collections and Guava have several implementations for that. Multimaps allow for multiple keys by maintaining a collection of values per key, i.e. you can put a single object into the map, but you retrieve a collection.
If you can use Java 5, I would prefer Guava's `Multimap` as it is generics-aware.
Problem
I want to have a map with duplicate keys. I know there are many map implementations (Eclipse shows me about 50), so I bet there must be one that allows this. I know it's easy to write your own map that does this, but I would rather use some existing solution. Maybe something in commons-collections or google-collections?