Design decisions: Why and when to make an interface private?

Question

Are private interfaces ever used in design decisions ? If so, what are the reasons and when do you know the need for a private interface?

Answer 1

It has to be package protected if the interface if for internal use. In general if the interface hasn't any interest outside it's ambit it's a good api design decision to hide it because there's less complexity for the users of the interface and also allows you to refactor it more easily, because when the interface is public and in the API you loss the liberty to change it.