I recently attended an interview at Nagarro for a Java Backend role.

Core Java

1. Difference between abstract class and interface
2. what are default methods in interfaces?
3. What happens if two interfaces have same default methods?
4. Difference between Comparator and Comparable
5. HashMap & TreeSet internally working

Multithreading & Concurrency
6. Runnable vs Callable – when to use which?

7. What is the volatile keyword in Java?
8. Explain ConcurrentHashMap (internal working)
9. Compeltable Future & Future
10. Write Even Odd program using wait notify

Java 8 Features
11. What are terminal vs intermediate operations in Streams?

12. Stream vs Parallel Stream internal working of stream.

He Asked Scenario Baed Question

13. Your API is handling 1000k+ requests/sec and performance is degrading. How would you scale and optimize it?

14. You are building a payment API and receiving duplicate requests. How will you ensure idempotency?

15. Money is deducted from the account but order creation fails. How will you ensure data consistency?
    -------------------------------------------SpringBoot & Microservices
    What is auto-configuration in Spring Boot? How does it work?

16. What is the use of @SpringBootApplication?

17. What are Spring Boot starters?

18. What is dependency injection? Types?

19. How do you validate request payloads?

20. How does Spring Boot auto-configure beans?

21. How will you implement caching?

22. How will you design a scalable system in Spring Boot?

23. ApiGateway, LoadBalancer

24. Which Design pattern you have used recently?
    -------------------------------------------Coding Questions

25. Largest odd lenth string

26. Minimum steps to reach stairs

27. 2nd non repeating using Streams Java8

28. Group Employee by department and their roles

29. Mergesort code

30. Longest non repeating substring

31. Largest subarray with sum 0