You've got Observer down.
What you covered
💡 The Bottom Line, one more time
Observer pattern explained: define a one-to-many dependency so that when one object changes state, all its dependents are notified.
What's next
Observer is one of 23 classic Gang-of-Four patterns. From here, the natural next step is:
- Explore more patterns — see the full Design Patterns track for all 23, grouped by Creational, Structural, and Behavioral.
- SOLID Design Principles — many patterns, including this one, are concrete applications of SOLID principles.