Revision Notes/Design Patterns
Field Entry - Design Patterns
Observer Pattern
Defines a one-to-many dependency so when one object (subject) changes state, all its dependents (observers) are notified automatically.
Field Note - Real-world Analogy
“Like subscribing to a YouTube channel. You (observer) click Subscribe on a channel (subject). When the channel uploads a video (state change), YouTube notifies all subscribers automatically. You can Unsubscribe any time. The creator doesn't personally know or contact each subscriber — it all goes through the platform's notification system.”
Field Observations - Key Topics Covered
The problem: one object changes and several other objects need to react. Without Observer, the subject would need to know about every dependent and call them directly — tight coupling that gets messy fast. Adding a new dependent means modifying the subject.
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