If the base type of the set is a bit set, the function need only worry about the position of each bit, and not the intended type. Of course, if the set has content in hash buckets (or a similar scheme), you would need to pass in some kind of comparator function/callback.

I say this as a former C programmer used to doing such things to make library routines like "bsearch()" work.

Too many things in Java rely on subclassing, rather than functional composition.