How to use Sets as keys in Java Maps

Question

I have a Map that uses a Set for the key type, like this:

Map, Val> map;

When I query map.containsKey(myBunchOfThing

Answer 1

Did you modify the set after insertion? If so, it's possible the set got sorted into a different bucket than the one it's looking in. When iterating, it does find your set, because it looks in the whole map.

I believe the contract for HashMap states you're not allowed to modify the hashcode for objects used as a key,