Bird
Raised Fist0

You implemented the Observer pattern but observers are not notified when the subject changes. What is the most likely cause?

medium📝 Analysis Q6 of Q15
LLD - Behavioral Design Patterns — Part 2
You implemented the Observer pattern but observers are not notified when the subject changes. What is the most likely cause?
ASubject does not maintain a state
BObservers are not registered with the subject
CObservers do not implement the update method
DSubject calls update on observers
Step-by-Step Solution
Solution:

  1. Step 1: Check observer registration

    Observers must be registered with the subject to receive notifications.

  2. Step 2: Identify missing registration

    If observers are not registered, they won't be notified despite subject changes.

  3. Final Answer:

    Observers are not registered with the subject -> Option B

  4. Quick Check:

    Missing registration = No notifications [OK]
Quick Trick: Register observers to get notified [OK]
Common Mistakes:
MISTAKES
  • Assuming subject state is mandatory
  • Ignoring observer interface implementation
  • Thinking subject calls update incorrectly

Want More Practice?

15+ quiz questions · All difficulty levels · Free

Free Signup - Practice All Questions
More LLD Quizzes
Behavioral Design Patterns — Part 2 - Memento pattern - Quiz 3easy Behavioral Design Patterns — Part 2 - Visitor pattern - Quiz 6medium Design — Elevator System - Emergency handling - Quiz 14medium Design — Library Management System - Why library management tests CRUD design - Quiz 9hard Design — Library Management System - Fine calculation - Quiz 13medium Design — Library Management System - Class design (Book, Member, Librarian, Loan) - Quiz 11easy Design — Tic-Tac-Toe Game - Requirements and game rules - Quiz 1easy Design — Tic-Tac-Toe Game - Move validation - Quiz 7medium Design — Tic-Tac-Toe Game - Player turn management - Quiz 13medium Design — Tic-Tac-Toe Game - Move validation - Quiz 6medium