Why is it useful to be able to add private methods to interfaces?

What will be an ideal response?

A class’s private helper methods may be called only by the class’s other methods. As of Java SE 9, you can declare helper methods in interfaces via private interface methods. An interface’s private instance methods can be called directly (i.e., without an object reference) only by the interface’s other instance methods. An interface’s private static methods can be called by any of the interface’s instance or static methods