code: public void addListener(UpdateCheckListener newListener) {
          if (newListener == null) {
              throw new IllegalArgumentException("newListener");
          }
          GatewayVersion latestGatewayVersion = getLatestGatewayVersion();
          if (latestGatewayVersion != null && latestGatewayVersion.compareTo(currentVersion) > 0) {
              newListener.newVersionAvailable(currentVersion, latestGatewayVersion);
          }
          listeners.add(newListener);
      }
docs: Adds an @UpdateCheckListener who will be notified when the version changes,
  
  @param newListener