code: public static void setPreferencesHandler(Object target, Method prefsHandler) {
          boolean enablePrefsMenu = (target != null && prefsHandler != null);
          if (enablePrefsMenu) {
              setHandler(new OSXAdapter("handlePreferences", target, prefsHandler));
          }
          // If we're setting a handler, enable the Preferences menu item by calling
          // com.apple.eawt.Application reflectively
          try {
              Method enablePrefsMethod = macOSXApplication.getClass().getDeclaredMethod("setEnabledPreferencesMenu", new Class[] { boolean.class });
              enablePrefsMethod.invoke(macOSXApplication, new Object[] { Boolean.valueOf(enablePrefsMenu) });
          } catch (Exception ex) {
              System.err.println("OSXAdapter could not access the About Menu");
              ex.printStackTrace();
          }
      }
docs: They will be called when the Preferences menu item is selected from the application menu