我在blackberry的下面的代码中得到了ClassCastException

Question

UiApplication.getUiApplication().invokeLater(new Runnable() {   
     public void run() {
        Screen screen = UiApplication.getUiApplication().getActiveScreen();
        System.out.println("Screen == "+screen);    
        if (screen instanceof PushNotificationsScreen) {
            System.out.println("Push Notification Screen");    
            PushNotificationsScreen pns = (PushNotificationsScreen) screen; 
            pns.update();    
        }   
    }   
});