You need to design a notification system that supports multiple types of state changes and notifies observers only for the types they subscribed to. Which design approach is best?

hard📝 Trade-off Q8 of 15

LLD - Design — Online Shopping Cart

AUse a Singleton pattern to manage all notifications globally.

BUse a Decorator pattern to add notification behavior dynamically.

CUse a Factory pattern to create different observer objects.

DUse the Observer pattern with event types and filter notifications by type.

Step-by-Step Solution

Solution:

Step 1: Understand requirement for event filtering
Observers want notifications only for specific state change types, so filtering is needed.
Step 2: Match design pattern to filtering need
Observer pattern extended with event types allows selective notification, fitting the requirement best.
Final Answer:
Use the Observer pattern with event types and filter notifications by type. -> Option D
Quick Check:
Selective notify = Observer with event filtering [OK]

Quick Trick: Add event types to Observer pattern for selective notify [OK]

Common Mistakes:

Choosing Singleton which lacks filtering
Using Factory which only creates objects
Applying Decorator which adds behavior but not filtering

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You need to design a notification system that supports multiple types of state changes and notifies observers only for the types they subscribed to. Which design approach is best?

Step 1: Understand requirement for event filtering

Step 2: Match design pattern to filtering need

Final Answer:

Quick Check:

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