Question

I have several Sets that store the objects of the same class, but I want to specify a different identity function for each of them (i.e. say, in one set A==B if A.x==B.x, while in another A==B if A.y==B.y).

Currently I use TreeSets with different Comparators defined for each. I am wondering how the same thing can be done if I want to switch to HashSets. Java does not allow passing a separate hash function in the same way it allows Comparators for Sorted/Tree-based Collections. The only way that I can think of doing it would involve creating a different wrapper class and implementing the hashCode() method in each for the elements of each HashSet. Is there a better way of doing this?

Answer 1

You could try using THashSet in GNU Trove, This support multiple hashing strategies.