Interview Q&A / Object-Oriented Programming

1. What is the difference between the Observer pattern and Publish-Subscribe?

   In Observer, observers register directly with the subject and the subject calls them. In Pub-Sub, a message broker sits between publishers and subscribers, so neither knows the other.

   IntermediateQuick answer1 min read
2. Why must you unsubscribe observers, and how do you design for it?

   A subject holds strong references to its observers, so a forgotten one stays in memory and keeps receiving events. Return an unsubscribe function from subscribe() and call it when done.

   IntermediateQuick answer1 min read