question: public void subscription ( String topic , int qos , boolean sub ) { setTitleText ( "" ) ; if ( connected ) { try { String [ ] theseTopics = new String [ 1 ] ; int [ ] theseQoS = new int [ 1 ] ; theseTopics [ 0 ] = topic ; theseQoS [ 0 ] = qos ; synchronized ( this ) { if ( sub ) { writeLogln ( "  --> SUBSCRIBE,        TOPIC:" + topic + ", Requested QoS:" + qos ) ; } else { writeLogln ( "  --> UNSUBSCRIBE,      TOPIC:" + topic ) ; } } if ( sub ) { mqtt . subscribe ( theseTopics , theseQoS ) ; } else { mqtt . unsubscribe ( theseTopics ) ; } } catch ( Exception ex ) { setTitleText ( "MQTT subscription exception caught !" ) ; JOptionPane . showMessageDialog ( frame , ex . getMessage ( ) , "MQTT Subscription Exception" , JOptionPane . ERROR_MESSAGE ) ; } } else { setTitleText ( "MQTT client not connected !" ) ; } }
target:  This method is called when either the subscribe or unsubscribe buttons are pressed. It performs the  MQTT subscribe or unsubscribe and writes an entry in the history log if the history window is open.<BR> Any exceptions are caught and displayed in a dialog box.