Java built-in Observable push notifications

I am trying to understand how to implement push vs pull notifications using Java built-in Observer.

the Observable class has 2 methods notifyObservers() and notifyObservers(Object arg) I want to understand the differnce between them.

so I tried this

@Override
    public void update(Observable o, Object arg) {
        /*
        if (o instanceof WeatherData) {
            WeatherData weatherData = (WeatherData) o;
            this.temperature = weatherData.getTemperature();
            this.humidity = weatherData.getHumidity();
        }*/

        if (arg instanceof WeatherData) {
        WeatherData weatherData = (WeatherData) arg;
        this.temperature = weatherData.getTemperature();
        this.humidity = weatherData.getHumidity();
        }

        display();
    }

and in my observable class

setChanged();
        //notifyObservers();
        notifyObservers(this);

both objects can be cast down to WeatherData(the Observer) and then get the data from them.

using both methods seem like push notification-type for me, so what is the difference? and how can I implement pull notification-type using it?