Preparing for a Java full-stack developer interview can feel a bit overwhelming, especially with so much to cover. But don’t worry, I’ve got you!

In this blog, you’ll find a collection of 200+ interview questions that touch on everything you need to know—Core Java, backend frameworks like Spring and Hibernate, frontend tools like React, and even databases. Whether you’re brushing up or diving deeper, these questions are here to help you feel more confident and ready.

Let’s dive in and make your prep easier!

Core Java

OOP Concepts

  1. What are the four pillars of Object-Oriented Programming (OOP)? Show Answer
  2. Explain the difference between abstraction and encapsulation. Show Answer
  3. How does inheritance work in Java? Provide an example. Show Answer
  4. What is polymorphism, and what are its types? Show Answer
  5. Can you override static methods in Java? Why or why not? Show Answer
  6. What is the difference between method overloading and method overriding? Show Answer
  7. Explain the concept of super and this keywords. Show Answer
  8. How do you implement multiple inheritances in Java? Show Answer

Exception Handling

  1. What is the difference between checked and unchecked exceptions? Show Answer
  2. How does try-catch work in Java? Show Answer
  3. Explain the role of finally block in exception handling. Show Answer
  4. Can you have multiple catch blocks for a single try block? Show Answer
  5. What is the purpose of the throw and throws keywords? Show Answer
  6. How would you create a custom exception in Java? Show Answer

Collections Framework

  1. What is the difference between ArrayList and LinkedList? Show Anwser
  2. How does HashMap work internally in Java? Show Anwser
  3. What is the difference between HashSet and TreeSet? Show Anwser
  4. What are the differences between List, Set, and Map? Show Anwser
  5. Explain the concept of fail-fast and fail-safe iterators. Show Anwser
  6. How is ConcurrentHashMap different from HashMap? Show Anwser
  7. When would you use a PriorityQueue? Show Anwser
  8. What are the differences between Stack and Deque? Show Anwser

Multithreading and Concurrency

  1. What is the difference between Thread and Runnable?
  2. How does synchronization work in Java?
  3. Explain the concept of thread safety.
  4. What is the difference between wait() and sleep() methods?
  5. How do you implement thread communication in Java?
  6. What are volatile and transient keywords?
  7. How does the ExecutorService framework work?
  8. What is the difference between Callable and Runnable?
  9. How do you handle deadlocks in a multithreaded environment?

Java 8 Features

  1. What are the key features introduced in Java 8?
  2. Explain the concept of Lambda expressions.
  3. What is a functional interface? Provide examples.
  4. How does the Stream API work in Java 8?
  5. What is the purpose of the Optional class?
  6. Explain the difference between map() and flatMap().
  7. How does method reference work in Java?
  8. What are default methods in interfaces?
  9. What is the Collectors utility class?

Java Basics

  1. What are the access modifiers in Java?
  2. Explain the lifecycle of a Java program.
  3. What is the significance of the main() method?
  4. What are Java packages, and why are they used?
  5. How does garbage collection work in Java?
  6. Explain the concept of String, StringBuilder, and StringBuffer.
  7. What is the difference between == and equals()?
  8. What are wrapper classes in Java?
  9. How does autoboxing and unboxing work?
  10. What is the difference between final, finally, and finalize()?

Backend Development

Spring Framework

  1. What are the main features of the Spring Framework?
  2. Explain the concept of Dependency Injection (DI).
  3. What are the different types of DI in Spring?
  4. What is the role of the @Autowired annotation?
  5. How do you define a Spring Bean?
  6. What is the difference between @Component, @Service, and @Repository?
  7. What is Aspect-Oriented Programming (AOP) in Spring?
  8. Explain the use of @Transactional annotation.
  9. How does Spring Boot simplify application development?
  10. What is the role of the application.properties or application.yml file?
  11. How do you create a RESTful API using Spring Boot?
  12. What is the role of @RestController?
  13. How do you handle exceptions in Spring Boot?
  14. What is the purpose of Spring Security?
  15. How does Spring Data JPA work?

Hibernate

  1. What is Hibernate, and why is it used?
  2. Explain the difference between Session and SessionFactory.
  3. What is the purpose of an HQL query?
  4. How does Hibernate handle caching?
  5. What are the different types of associations in Hibernate?
  6. What is the difference between get() and load() methods?
  7. Explain the concept of lazy and eager fetching.
  8. What are entity states in Hibernate?

Frontend Development

HTML/CSS/JavaScript

  1. What are semantic elements in HTML?
  2. How does the box model work in CSS?
  3. Explain the difference between id and class selectors in CSS.
  4. How do you implement responsiveness in a web application?
  5. What is the difference between inline, block, and inline-block elements?
  6. What are closures in JavaScript?
  7. How does event delegation work in JavaScript?
  8. What is the purpose of async and await?
  9. Explain the difference between var, let, and const.

React

  1. What is React, and why is it used?
  2. Explain the concept of Virtual DOM.
  3. What are React hooks? Provide examples.
  4. How do you manage state in React?
  5. What is the difference between functional and class components?
  6. How does React handle component lifecycle?
  7. What are higher-order components (HOCs) in React?
  8. How do you optimize React applications?
  9. What is the purpose of useEffect?

Database

SQL

  1. What are the different types of SQL joins?
  2. How do you optimize SQL queries?
  3. Explain the concept of indexing.
  4. What is the difference between WHERE and HAVING clauses?
  5. How do you handle transactions in SQL?
  6. What is normalization in databases?
  7. Explain the concept of ACID properties.

NoSQL

  1. What is NoSQL, and when should it be used?
  2. How does MongoDB differ from relational databases?
  3. What are collections and documents in MongoDB?

Other Topics

DevOps

  1. What is CI/CD, and how does it work?
  2. What tools have you used for deployment?
  3. How do you manage environment configurations?

Testing

  1. How do you write unit tests for Java applications?
  2. What are mocks and stubs in testing?
  3. How do you test REST APIs?

Performance

  1. How do you handle high concurrency in web applications?
  2. What strategies have you used for caching?
  3. How do you handle memory leaks in Java?