What is the Singleton pattern and why is it used?

Short answer: The Singleton pattern ensures a class has only one instance and provides a global point of access to it. It’s commonly used when exactly one object is needed to coordinate actions across the system, such as configuration settings, logging, or caching.

Real-world example (ShopNest)

ShopNest payment fees use Strategy: IFeeCalculator with UPI/Card implementations chosen at runtime.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.