Ptolemy

module Subject {
    int count;

    void increment() {
        count++;
    }

    int getCount() {
        return count;
    }
}

module Observer {
    void update(int value) {
        System.out.println("Observer notified: " + value);
    }
}

module Main {
    public static void main(String[] args) {
        Subject s = new Subject();
        Observer o = new Observer();
        s.increment();
        s.increment();
        System.out.println("Count: " + s.getCount());
        o.update(s.getCount());
    }
}