Recently, I appeared for a Java Software Development Engineer (SDE-1) interview that focused on object-oriented programming concepts, collections, concurrency, and design-based problem-solving. The entire discussion lasted around one hour and was divided into clearly structured sections.
Below is a detailed breakdown of the questions that were asked.
1. Explain the four main pillars of OOP in your own words with small examples.
Expected focus areas: Encapsulation, Abstraction, Inheritance, and Polymorphism.
2. What is the difference between an interface and an abstract class? When would you use each?
3. What happens when you override equals() but not hashCode()?
4. Suppose you have a list of Employee objects. You need to remove all duplicates and sort them by salary in descending order. How would you do it?
5. Explain the difference between ArrayList, LinkedList, and HashSet.
6. What is a fail-fast versus fail-safe iterator? Provide examples.
7. If you had to design a custom data structure that keeps items in sorted order and allows fast lookup, what Java class would you start from?
8. How do you make a method thread-safe in Java?
9. Two threads access a shared counter. Sometimes the counter shows incorrect results. How would you fix it?
10. What is a deadlock? Give a simple example.
This experience serves as a good benchmark for anyone preparing for Java SDE-1 or entry-level backend engineering interviews.