Inject an Interface field implemented by an Activity

AnnotationsUtil.java

public static void injectCallbacks(Fragment fragment) {
    injectCallbacks(fragment, fragment.getActivity());
}

public static void injectCallbacks(Object obj, Activity activity) {
    Field[] fields = obj.getClass().getDeclaredFields();
    for (Field field : fields) {
        if (field.isAnnotationPresent(InjectCallback.class)) {
            try {
                field.setAccessible(true);
                field.set(obj, activity);
            } catch (IllegalAccessException e) {
                throw new RuntimeException(e);
            } catch (IllegalArgumentException e) {
                throw new ClassCastException(activity.getClass().getSimpleName() + " must implement " + field.getType().getSimpleName());
            }
        }
    }
}

InjectCallback.java

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface InjectCallback {

}