Java many to many association map

Question

I have two classes, ClassA and ClassB, as well as a \"many to many\" AssociationClass. I want a structure that holds the associations

Answer 1

Here's my implementation based on guava Multimap:

public class ImmutableBiMultimap {
    private final ImmutableSetMultimap kToV;
    private final ImmutableSetMultimap vToK;

    public ImmutableBiMultimap (SetMultimap keyToValueMap) {
        kToV = ImmutableSetMultimap.copyOf(keyToValueMap);

        SetMultimap valueToKeyMap = HashMultimap.create();
        for (Entry entry : kToV.entries()) {
            valueToKeyMap.put(entry.getValue(), entry.getKey());
        }

        vToK = ImmutableSetMultimap.copyOf(valueToKeyMap);
    }

    public ImmutableSet getValuesForKey(K key) {
        return kToV.get(key);
    }

    public ImmutableSet getKeysForValue(V value) {
        return vToK.get(value);
    }
}