Question

Possible Duplicate:
Bidirectional multi-valued map in Java

I need a data structure that implements a N-to-N relation. Something like a Map<Foo,Bar> with calls:

getValues(Foo foo): Collection<Bar>
getValues(Bar bar): Collection<Foo>

and methods for the usual management like:

removeKey(Foo)   [remove all the <Foo,X> entries]
removeValue(Bar) [remove all the <X,Bar> entries]

Is there some library I can use or should I implement it? Thanks

Answer 1

Why not create 2 maps, each one from the key to collection of values:

Map<Foo, Collection<Bar>> and Map<Bar, Collection<Foo>>

If you wish you can create a class to wrap (Maybe use some generics for the types so you can easily reuse it) them inside and provide the methods you need