en/videos/advanced/java/oop/design_patterns/observer

👀 Observer Design Pattern in Java

The Observer Pattern is a behavioral design pattern that defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. It's widely used in event handling systems, GUI frameworks, and data-binding scenarios.

📌 Key Concepts

• Subject: Maintains a list of observers and notifies them of state changes.
• Observer: Defines an update interface to receive notifications from the subject.
• ConcreteSubject: Implements the subject interface and updates observers when its state changes.
• ConcreteObserver: Implements the observer interface to react to notifications.

🧩 Real-World Example

Imagine a news agency (ConcreteSubject) that notifies subscribers (ConcreteObserver) when a new article is published. Subscribers can listen for updates on specific topics like tech, sports, or politics.

// Observer Pattern Example
interface Observer {
    void update(String news);
}

interface Subject {
    void registerObserver(Observer observer);
    void notifyObservers();
}

class NewsAgency implements Subject {
    private List<Observer> observers = new ArrayList<>();
    private String latestNews;

    @Override
    public void registerObserver(Observer observer) {
        observers.add(observer);
    }

    @Override
    public void notifyObservers() {
        for (Observer observer : observers) {
            observer.update(latestNews);
        }
    }

    public void setNews(String news) {
        latestNews = news;
        notifyObservers();
    }
}

class NewsSubscriber implements Observer {
    @Override
    public void update(String news) {
        System.out.println("Subscriber received: " + news);
    }
}

🚀 Use Cases

• Event Handling: GUI components (e.g., buttons, text fields) notify listeners when events occur.
• Data Binding: UI elements automatically update when underlying data changes.
• Publish-Subscribe Systems: Messaging platforms or chat applications.

📚 Extend Your Learning

For a deeper dive into design patterns, check out our design_patterns/videos collection.