（省略） public class UIActivator implements BundleActivator { （省略）    @Override    public void start(BundleContext context) throws Exception {       bundle = context.getBundle();       if(tracker == null){          tracker = new ServiceTracker(context, INotificationService.class.getName(),null);       }       tracker.open(true);       createOpenTimer();    } （省略）    private void createOpenTimer() {       openTimer = new Timer();       openTimer.scheduleAtFixedRate(new TimerTask(){          @Override          public void run() {             final List<INotificationMessage> contents = new ArrayList<INotificationMessage>();             Object[] services = tracker.getServices();             if(services == null) return;             for(Object obj : services){                INotificationService service = (INotificationService) obj;                contents.addAll(service.getContents());             } （省略）    public void stop(BundleContext context) throws Exception {       openTimer.cancel();       openTimer.purge();       openTimer = null;       tracker.close();       tracker = null; （省略） }