Compares two event classes based on their position in a class hierarchy. Classes higher up in a hierarchy are 'greater than' (ordered later) than classes lower in a hierarchy (ordered earlier). Classes in unrelated hierarchies have the same order priority. <p/> Event bus implementations use this comparator to determine which event listener method to invoke when polymorphic listener methods are defined: <p/> If two event classes exist A and B, where A is the parent class of B (and B is a subclass of A) and an event subscriber listens to both events: <pre> @Subscribe void onEvent(A a) { ... }