What is the main task of the notify method in a notification or observer system?

The notify method in a notification system or observer pattern is responsible for alerting all registered observers (subscribers) about changes in the state of the subject (observed object). When the object's state changes, notify is called, which iterates through all subscribers and calls their update method, passing the current data.

Example in Java:

interface Observer {
    void update(String message);
}

class Subject {
    private List<Observer> observers = new ArrayList<>();

    void addObserver(Observer o) {
        observers.add(o);
    }

    void notifyObservers(String message) {
        for (Observer o : observers) {
            o.update(message);
        }
    }
}

Thus, the main task of notify is to ensure the distribution of notifications to all interested objects when the state changes.