Using pointer equality is fine, but doesn't help in the case where you have a custom equals() implementation. Maybe the JVM could inspect the implementation of equals() and spot certain patterns (e.g. it's the conjunction of equals() of a set of constituent objects), but doing it in general sounds impossible to me.
For hash tables where the number of buckets is much smaller than the number of hash codes (i.e. all of them) and where hash codes are well distributed and collisions are caused by different hash codes mapping onto the same bucket (not always true, but often), the tree can be implemented by comparing hash codes, with a fallback to handle the case of multiple identical hash codes.
