Java outer-class access to inner-class interface constants

Excude me if this is a dumb question.

I have a "Fragment" outer-class with and inner-class interface. This interface is only implemented by one other Activity-class using "implements OuterFragment.ParentActivityListener".

I would like to have a few constants to use with the interface methods. But these constants also needs to be available in the outer-class. Is there a way to access them from the outer-class as shown below? Is this a bad pattern to use, even though there will be a very limited use of this interface (=1)?

public class OuterFragment extends Fragment {

    public interface ParentActivityListener {
        public int OKBUTTON = 5;
        public void onPlayertimerMessage(int idFromFragment, int idFromPosition, int iAction);
    }
    @Override
    public View onCreateView(LayoutInflater inflater, 
            ViewGroup container, Bundle savedInstanceState) {
          // Access interface constant from here?
    }

}

Any input appreciated!

If it's a constant, it should be static and final :

public static final int OKBUTTON = 5;

And you access it with OuterFragment.ParentActivityListener.OKBUTTON.