A bimap allows the user to have an inverse view but constrains the user to have unique keys K and values V so that it can return an inverted map V -> K

A multimap allows the user to have multiple values for the same key.

The ImmutableMultiBimap allows the user to have non-unique values V for different keys K and inverts them into a map that returns a V -> Set<K> map.

For example,

ImmutableBiMap<String, Integer> bimap = ImmutableBiMap.of("One", 1, "Two", 2); ImmutableBimap<Integer, String> inverseMap = bimap.inverse();

Will give you an inverseMap having values

[ 1 -> "One" ], [ 2 -> "Two"]

But the ImmutableBiMap throws an exception if you try to instantiate like so

ImmutableBiMap<String, Integer> bimap = ImmutableBiMap.of("One", 1, "Two", 1);

Because it has no way to invert the map.

A MultiSet allows the user to have multiple values for the same key. For instance,

ImmutableMultimap<String, Integer> multimap = ImmutableMultimap.of("One", 1, "One", 2);

Will give the user a map like so

[ "One" -> Collection<Integer>[1, 2]]

The ImmutableMultiBimap allows the user to have a non-unique set of vaues as well as inversion by making a Multimap out of the inversion.

ImmutableHashMultiBimap<String, Integer> map = ImmutableHashMultiBimap.of("Hello", 1, "World", 1); Multimap<Integer, String> mapInverse = map.inverse();

Will give

mapInverse = [1 -> ["Hello", "World"]]