Leveraging the Observer Design Pattern : 10 Real-World Examples in Action

4 minute read

The Observer Design Pattern is a behavioral design pattern that allows an object (the subject) to notify multiple dependent objects (the observers) about changes in its state without knowing who or what those observers are. This pattern is widely used in software systems that require real-time updates or notifications. In this article, we will explore 10 real-world applications where the Observer Pattern is used to enable real-time communication, updates, or notifications.

1. Social Media Notifications

Description: Social media platforms, such as Facebook, Twitter, and Instagram, notify users of likes, comments, shares, and messages. These notifications keep users engaged and informed of activities on their posts and accounts they follow.

Observer: Users who follow posts, pages, or accounts and receive updates about activities on them.

Subject: Posts, accounts, or events that trigger notifications.

How It Works: When a user subscribes to a post or account, the system treats them as observers. When an activity (like, comment, share) occurs on the post, the platform (subject) notifies all the users observing it.

2. Chat Applications

Description: Messaging platforms, like WhatsApp and Slack, send real-time notifications to users when they receive new messages or mentions. This allows users to stay up-to-date with conversations even when they aren’t actively looking at the app.

Observer: Members of a chat group or users in a direct message thread.

Subject: The chat group or message thread where new messages are posted.

How It Works: Users subscribe to chat groups or message threads. When a new message is posted, the system (subject) notifies all users observing that group or conversation.

3. Online Shopping and Stock Alerts

Description: E-commerce platforms such as Amazon and eBay use the Observer Pattern to notify users about price changes, product restocks, or special promotions.

Observer: Customers who subscribe to updates for specific products.

Subject: The product or offer being tracked by the customer.

How It Works: Customers subscribe to specific products, and when any change occurs (e.g., price drop, availability), the platform (subject) notifies all users who have subscribed to that product.

4. Event-Driven Monitoring Systems

Description: IT infrastructure monitoring tools, such as Nagios and Datadog, monitor various metrics (e.g., server uptime, CPU usage, or disk space) and alert system administrators when an issue arises.

Observer: System administrators or monitoring teams who need real-time alerts.

Subject: The monitored system or resource, such as a server or application.

How It Works: The system (subject) tracks key metrics (e.g., CPU usage). If the metric crosses a predefined threshold, the system triggers a notification to all observers (admins) who are subscribed to the metric.

5. News Feed Subscriptions

Description: News platforms like Google News, BBC, and CNN allow users to follow specific topics, authors, or categories. When a new article is published under a subscribed category or by a followed author, users are notified immediately.

Observer: Users who subscribe to categories or authors.

Subject: Articles or content within a specific category or published by a specific author.

How It Works: When new content is published, the platform (subject) sends real-time updates to all users who are observing the particular topic or author.

6. Gaming Leaderboards

Description: Online games, like Fortnite or PUBG, notify players of leaderboard changes, upcoming challenges, or rewards.

Observer: Players who track the game’s leaderboard or their in-game performance.

Subject: The game’s leaderboard or event system.

How It Works: Players subscribe to notifications about leaderboard updates. When their rank changes or when a new event is available, the game (subject) sends an update to the players observing the leaderboard.

7. IoT Systems

Description: Smart home devices, such as thermostats (Nest), security cameras, and smart lights, notify users of changes or status updates in real time.

Observer: Homeowners or users accessing the smart home system via an app or device.

Subject: IoT devices, such as cameras, thermostats, or motion detectors.

How It Works: The IoT system (subject) monitors connected devices. When a change occurs (e.g., door opens, temperature rises), the system sends notifications to the users (observers) who are subscribed to those events.

8. Auction Platforms

Description: Auction platforms, such as eBay, notify participants of new bids, bid price changes, or auction closing times.

Observer: Bidders participating in an auction.

Subject: The auction itself, including the item being sold.

How It Works: When users place bids on an item, they subscribe to updates. If a bid is placed or the auction is about to close, the platform (subject) notifies all active bidders.

9. Real-Time Traffic Updates

Description: Navigation apps like Google Maps and Waze notify users about traffic conditions, road closures, or new incidents along their route.

Observer: Drivers using the navigation system.

Subject: The route being taken by the user and the traffic data related to it.

How It Works: When drivers enter a route, they subscribe to real-time updates. The navigation system (subject) continuously monitors traffic data, and when there’s a change (e.g., a crash or road closure), it sends an update to users along the route.

10. Stock Market and Cryptocurrency Tracking

Description: Stock market applications such as Robinhood, E*TRADE, or cryptocurrency platforms like Coinbase notify users of price changes, market trends, or news affecting the stocks or cryptocurrencies they are following.

Observer: Investors or traders who are tracking specific financial assets.

Subject: The asset (e.g., a stock, cryptocurrency) being tracked.

How It Works: Users subscribe to specific stocks or cryptocurrencies. When the price or market trend changes, the system (subject) sends an update to all observers who have subscribed to the asset.

Conclusion

The Observer Design Pattern is invaluable when building systems that require real-time updates or notifications. Whether it’s used for social media notifications, real-time chat alerts, or system monitoring, the Observer pattern ensures that interested parties are notified as soon as an update occurs, improving responsiveness and interactivity. Understanding its real-world applications can help in architecting software systems that are both efficient and scalable.