Only the enclosing class can access a Static Nested interface.

Consider following code in which interface Xyz is enclosed in

class Abc.

public class Abc {

public interface Xyz {

void callback();

}

public static void registerCallback(Xyz xyz) {...}

}

// Client Code

Abc.registerCallback(new Abc.Xyz() {

public void callback() {...}

});

Any code that cannot access Abc can not access interface Xyz also.

So the purpose of declaring an Inner interface is to restrict its

access from outside world

https://www.javatpoint.com/nested-interface#:~:text=The%20nested%20interfaces%20are%20used,can't%20be%20accessed%20directly.