Observer Pattern Explained: From School Bell to Order Events 🎯 Why This Pattern Matters In interviews, design patterns often pop up, and the Observer Pattern is one of the most asked. Instead of memorizing theory, let’s connect it to a story you’ll never forget — and then translate it into practical Java code you can actually show in an interview 📖 Story Analogy — The School Bell Think back to school days: At 12:30 PM, the bell rings. Students run to lunch. Teachers close books. The peon opens gates. 👉 The bell (Subject) doesn’t know or care who reacts. Each Observer does its own thing when notified. That’s the Observer Pattern: one subject, many independent observers reacting differently. 🧑💻 Practical Java Example — Order Placed Event Let’s switch from school to a real project example: e-commerce order placement. When an order is placed: Send confirmation email Write an audit log Update metrics Instead of hard-coding all in the service, we publish an event. Observers (list...