Hello, everyone!

As far as I know, things such as SortedMap or SortedSet, use compareTo (rather than equals) on Comparable<?> types for checking equality (contains, containsKey).

But what if certain types are equatable by concept, but not comparable?

I have to declare a Comparator<?> and override the method int compareTo(T o1, To2). OK, I can return 0 for instances which are considered equal. But, for unqeual instances, what do I return when an order is not evident?

Is the approach of using SortedMap or SortedSet on equatable but (by concept) not comparable types good anyway?

Thank you!

EDIT:
I don't want to store things sorted, but would I use "usual" Map and Set, I couldn't "override" the equality-behavior.

EDIT 2:
Why I can't just override equals(...): I need to alter the equality-behavior of a foreign class. Can't edit it.

EDIT 3:
Just think of .NET: They have IEquatable interface which cat alter the equality-behavior without touching the comparable behavior.