What are anti-patterns related to DI and Singleton?

Short answer: Service Locator anti-pattern: Hides dependencies instead of injecting them explicitly. Overusing Singleton: Leads to hidden global state and testing difficulties. Improper Singleton thread safety: Causes race conditions. Injecting concrete implementations: Violates DIP.

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.