Private Interfaces

Question

How can we use the methods of a private interface in our code?

Abstract classes are something which cannot be instantiated. So, if we need to use methods of abstract

Answer 1

You extend in same way your private interface as in case of classes. you can implement that interface outsite of visibility scope.

Answer 2

The private keyword means "anyone in the same class":

public class Foo {

   private interface X {...}
   private class X1 implements X {...}
}

This means all classes declared inside of Foo can use the interface Foo.X.

A common use case for this is the command pattern where Foo accepts, say, strings and converts them into internal command objects which all implement the same interface.

If you add a second class Bar to the file Foo.java, then it can't see Foo.X.