gistfile1.java

public class FooFragment {
    public interface IFooFragment {
        void onMapReady(GoogleMap map);
    }
    
    somewhereLaterInCode() {
        ((IFooFragment)getActivity()).onMapReady(myMap);
    }
}

public class MainActivity implements FooFragment.IFooFragment {
    
    .
    .
    .
    
    
    @Override
    public void onMapReady(GoogleMap map) {
        ((SomeOtherFragment)(getFragmentManager().getFragmentByTag("some_other_fragment"))).setMap(map);
    }
}