Using annotation to autmatically cast Android fragment callback. This automatically handles attach&detach fragment listeners for reducing Boilerplate code.

BaseCallbackFragment.java

public abstract class BaseCallbackFragment extends Fragment {

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    public @interface FragmentCallback {
        /**
        * Determine if throws excpetion if target does not implement the callback.
        * @return true: throws an exception if not implemented.
        */
        boolean mandatory() default true;
    }

    private List<Field> mFragmentCallbackFields = new ArrayList<>();

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        castFragmentCallback(activity);
    }

    private void castFragmentCallback(Context context) {
        for (Class<?> cls : this.getClass().getDeclaredClasses()) {
            FragmentCallback callback = cls.getAnnotation(FragmentCallback.class);
            if (callback == null)
                continue;
            for (Field f : this.getClass().getDeclaredFields()) {
                if (f.getType() != cls)
                    continue;
                String formatter = "%s must implement " + cls.toString();
                try {
                    if (getTargetFragment() != null) {
                        if (cls.isAssignableFrom(getTargetFragment().getClass())) {
                            if (!f.isAccessible())
                                f.setAccessible(true);
                            f.set(this, getTargetFragment());
                            mFragmentCallbackFields.add(f);
                        } else if (callback.mandatory())
                            throw new ClassCastException(String.format(formatter, getTargetFragment().toString()));
                    } else if (getParentFragment() != null) {
                        if (cls.isAssignableFrom(getParentFragment().getClass())) {
                            if (!f.isAccessible())
                                f.setAccessible(true);
                            f.set(this, getParentFragment());
                            mFragmentCallbackFields.add(f);
                        } else if (callback.mandatory())
                            throw new ClassCastException(String.format(formatter, getParentFragment().toString()));
                    } else {
                        if (cls.isAssignableFrom(context.getClass())) {
                            if (!f.isAccessible())
                                f.setAccessible(true);
                            f.set(this, context);
                            mFragmentCallbackFields.add(f);
                        } else if (callback.mandatory())
                            throw new ClassCastException(String.format(formatter, context.toString()));
                    }
                } catch (IllegalAccessException e) {
                    Logger.e(TAG, e.getMessage(), e);
                }

            }

        }
    }
    
    @Override
    public void onDetach() {
        super.onDetach();
        for (Field f : mFragmentCallbackFields) {
            try {
                f.set(this, null);
            } catch (IllegalAccessException e) {
                Log.e(TAG, e.getMessage(), e);
            }
        }
    }
}

Example:

public class EchoFragment extends BaseCallbackFragment {

    private FragmentInteractionListener mListener;

    @FragmentCallback
    public interface FragmentInteractionListener {
        void onEcho(EchoFragment fragment, String echo);
    }
}

public class MainFragment implements EchoFragment.FragmentInteractionListener  {

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        EchoFragment fg = new EchoFragment();
        fg.setTargetFragment(this, 0);
        getChildFragmentManager().beginTransaction().add(R.id.lo_fg_container, fg).commit();
    }

    @Override
    public void onEcho(EchoFragment fragment, String echo) {
         Log.d("MainFragment", echo);
    }
}