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

IMHO You cannot usefully make an interface private.

However I often have two interfaces, one for public use and one for internal use. The internal use interface I make package local if possible e.g.

public interface MyInterface {
   public void publicMethod();
}

interface DirectMyInterface extends MyInterface {
   public void internalUseOnlyMethod();
}

The internal use methods expose methods I don't want other developers to use and/or I want to be able to change easily. The reason I have the interface at all is that I have several implementations which I want to use internally via an interface.