This interface is for handling UnsolicitedNotificationEvent.

  This interface is for handling UnsolicitedNotificationEvent.
"Unsolicited notification" is defined in
RFC 2251.
It allows the server to send unsolicited notifications to the client.
A UnsolicitedNotificationListener must:

1. Implement this interface and its method
   
2. Implement NamingListener.namingExceptionThrown() so
   that it will be notified of exceptions thrown while attempting to
   collect unsolicited notification events.
   
3. Register with the context using one of the addNamingListener()
   methods from EventContext or EventDirContext.
   Only the NamingListener argument of these methods are applicable;
   the rest are ignored for a UnsolicitedNotificationListener.
   (These arguments might be applicable to the listener if it implements
   other listener interfaces).