Design Patterns: Intro & Observer Pattern

A Harry Potter Perspective - Observer: The Daily Prophet Subscription

Design Patterns in Software Development: A Harry Potter Perspective

Design patterns in software development are akin to the magical spells and enchantments in the wizarding world of Harry Potter. Just as wizards rely on various spells to achieve different outcomes, developers have a shared vocabulary of established design patterns, each serving a unique purpose in crafting clear and effective software architectures.

Every developer needs to know their toolkit: Exploring Design Patterns

In the realm of software development, there exist 23 established design patterns, categorized into creational, structural, and behavioral patterns. Each pattern serves as a tool in a developer's arsenal, empowering them to create scalable, maintainable, and efficient software systems.

Let's delve into some of these design patterns through the lens of the Harry Potter universe, bringing clarity to their concepts through familiar elements from the magical world.

Observer: The Daily Prophet Subscription

Overview:

The Observer design pattern, reminiscent of a wizard's subscription to the Daily Prophet, enables a system where multiple objects are notified of any updates or events occurring in another object. In the magical world, wizards subscribe to the Daily Prophet to stay informed about the latest news. Similarly, the Observer pattern allows objects (observers) to subscribe and receive notifications when the state of another object (subject) changes.

Explanation:

Picture yourself as a curious wizard eager to stay updated on the latest happenings in the magical realm. Instead of scouring the wizarding world for news, you subscribe to the Daily Prophet. The moment a new edition is published, you receive it automatically. The Observer pattern works similarly, establishing a mechanism where objects can subscribe and receive updates from a subject when its state changes.

Pseudo-code Example:

import java.util.ArrayList;
import java.util.List;

// Subject interface
interface MagicalNewsPublisher {
  void addObserver(WizardObserver observer);
  void removeObserver(WizardObserver observer);
  void publishNews(String headline);
}

// Concrete subject (Daily Prophet)
class DailyProphet implements MagicalNewsPublisher {
  private List subscribers = new ArrayList<>();
  private String latestHeadline;

  @Override
  public void addObserver(WizardObserver observer) {
    subscribers.add(observer);
  }

  @Override
  public void removeObserver(WizardObserver observer) {
    subscribers.remove(observer);
  }

  @Override
  public void publishNews(String headline) {
    this.latestHeadline = headline;
    notifySubscribers();
  }

  private void notifySubscribers() {
    for (WizardObserver subscriber : subscribers) {
      subscriber.update(latestHeadline);
    }
  }
}

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

// Concrete observer (Wizard)
class InformedWizard implements WizardObserver {
  private String name;

  public InformedWizard(String name) {
    this.name = name;
  }

  @Override
  public void update(String news) {
    System.out.println(name + " receives an update from the Daily Prophet: " + news);
  }
}

// Usage
DailyProphet dailyProphet = new DailyProphet();

Wizard harry = new InformedWizard("Harry");
Wizard hermione = new InformedWizard("Hermione");
Wizard ron = new InformedWizard("Ron");

// Wizards subscribe to updates from the Daily Prophet
dailyProphet.addObserver(harry);
dailyProphet.addObserver(hermione);
dailyProphet.addObserver(ron);

// Daily Prophet publishes a new headline, notifying all subscribers
dailyProphet.publishNews("Dark Mark Spotted Over Hogwarts!");

In this scenario, the DailyProphet represents the subject, notifying subscribed wizards (observers) about the latest headlines. The Observer pattern allows for a seamless communication channel, ensuring that wizards receive updates when significant events occur.

Summary:

The Observer pattern establishes a subscription mechanism where multiple objects (observers) are notified of any changes or events in another object (subject). Similar to wizards subscribing to the Daily Prophet for news updates, the Observer pattern enables a dynamic and efficient way for objects to stay informed about changes in the system.

**Note:** While the Observer pattern is magical, consider the frequency of notifications to prevent overwhelming observers. Also, choose this pattern when you have a clear distinction between subjects and observers, and the communication flow is one-way.