They can also be used to group static methods, including factories (Item 1), for objects that implement some interface, in the manner of java.util.Collections. (As of Java 8, you can also put such methods in the interface, assuming it’s yours to modify.)
>you can also put such methods in the interface
I'm not sure yet (haven't seen nor tried this, yet), but I don't think I like the idea of a more cluttered interface. That is, I'd err on keeping the utility methods separate.
