private static Event getEvent(String m, Kind entry) {
   String key = m + entry.toString();
   Event ev = eventCache.get(key);
   if (ev == null) { // store in the cache
     ev = new Event(m, entry);
     eventCache.put(key, ev);
   }
   return ev;
 }
 public int hashCode() {
   return (m + k.toString()).hashCode();
 }