Core Java Interview Questions for 2-5 Experienced Developers

In this article, we will discuss the frequently asked Core Java interview questions.

As probably you know that Core Java is base for any other Java-related technologies and frameworks. Every interviewer look for a candidate who has strong Core Java skillset.

In this article, I would like to share my experience with interviews from a small organization to MNC companies.

Check out my top articles related to Core Java interview preparation:

1. Top 10 Java main() Method Questions
2. 25+ OOPS Interview Questions
3. 25+ Java 8 Interview Questions
4. 25+ Java String Interview Questions
5. 25+ Java Exception Handling Questions

Here I will list out frequently asked Core Java interview questions that have been asked for me as well as my friends.

1. How HashMap works internally? [Solution]
2. What is the difference between Comparable and Comparator interface? [Solution]
3. What are oops principles? [Solution]
4. What are SOLID Principles?[Solution]
5. How to make the class as immutable?[Solution]
6. What is Serialization?[Solution]
7. What is Synchronization?[Solution]
8. What is fail-safe vs fail-fast Iterator in Java?[Solution]
9. What are Java 8 Features?[Solution]
10. What is the use of Lambda Expression?[Solution]
11. What is the use of Stream?[Solution]
12. What is the difference between Interface and Abstract class?[Solution]
13. What is a.hashCode() used for? How is it related to a.equals(b)?[Solution]
14. Why you need to override hashcode when you override equals in Java?[Solution]
15. What is the contract between equals and hashcode method?[Solution]
16. Difference between ArrayList and LinkedList in Java?[Solution]
17. What is the difference between Hashtable and HashMap?[Solution]
18. Can two equal object have the different hash code?[Solution]
19. What is the use of Serialize ID?[Solution]
20. What is the difference between String, StringBuilder, and StringBuffer?[Solution]
21. How to make a checked exception?[Solution]
22. How to make an unchecked exception?[Solution]
23. How to create custom exceptions?[Solution]
24. What is ConcurrentHashMap?[Solution]
25. What is the difference between Hashtable and ConcurrentHashMap?[Solution]
26. Can we override a static method? if no then why?[Solution]
27. What is fail fast and fail-safe in java?[Solution]
28. Why String is immutable in java?[Solution]
29. Why multiple inheritances are not supported in Java?[Solution]
30. How to detect deadlock and fix it?[Solution]
31. What is singleton and write code for singleton pattern?[Solution]
32. Difference between noclassdeffounderror and classnotfoundexception?[Solution]
33. Explain race condition in Java hashmap?[Solution]
34. Can we call a static method with a null object?[Solution]
35. How does volatile variable works in Java?[Solution]
36. What is a thread local variable in Java?[Solution]
37. Write code for thread-safe Singleton in Java?[Solution]
38. The difference between sleep and wait in Java?[Solution]
39. What is an immutable object? How do you create an Immutable object in Java?[Solution]

• Please share your interview questions at the comment section so that it will help others to prepare for an interview.