question: public void unsubscribe ( String topic , boolean existing ) throws Exception { logToFile ( "unsubscribe [topic:" + topic + "][existing:" + existing + "]" ) ; client . unsubscribe ( topic ) ; Object o = subscribedTopics . remove ( topic ) ; if ( existing == ( o == null ) ) { throw new Exception ( "Subscription state mismatch [topic:" + topic + "][expected:" + existing + "]" ) ; } }
target:  Unsubscribes the given topic