Top 30 Java Full Stack Developer Interview Questions (2025)

6. What is Pair Programming?

Two programmers work in partnership using pair programming to develop code together in  real-time. The driver takes responsibility for creating the code while the navigator checks the code to provide feedback and maintain its quality. The development methodology promotes team collaboration together with code improvement and mutual knowledge exchange.

7.  Explain the concept of CORS.

CORS stands for Cross-Origin Resource Sharing. Web browsers utilize  CORS as a security protocol that enables them to access resources from different domains than the page origin. Through permission management CORS defines which origins are allowed to access resources which protects against harmful cross-site attacks.

8. What is a callback function in JavaScript?

A callback function in JavaScript is a function that is passed as an argument to another function and is executed later, once a specific event or operation is completed. Callbacks are typically used for handling asynchronous operations, like network requests or timers, but they can also be used for other purposes, such as iterating over data or event handling.

Example

function greeting(name) {
  alert("Hello, " + name);
}

function processUserInput(callback) {
  var name = prompt("Please enter your name.");
  callback(name);  // The callback function is executed here
}

processUserInput(greeting);  // greeting is passed as a callback

9. What is Long polling and when it is used?

Long polling represents a web development method which enables web servers to deliver updates to clients without the  need for continuous client requests. The client-server connection remains active while the server delivers data only when it  becomes available.

• The client makes a server request
• The server maintains the open request until it generates  new information or the request expires
• Clients obtain fresh information which the server sends them
• The client sends  another request to maintain the open connection
• The process continues indefinitely

Applications which need immediate information updates like chat programs and collaborative editing tools benefit from this method. This method of server communication operates efficiently because it  lowers the number of unnecessary client requests and decreases the amount of work needed by the server.

10. What are the different types of CSS selectors?

CSS selectors can be:

• Basic selectors: element, id, class
• Combinator selectors: descendant (A B), child (A > B), adjacent sibling (A + B), general sibling (A ~ B)
• Group selectors: (A, B, C)
• Attribute selectors: ([attribute], [attribute="value"])
• Pseudo-classes: (:hover, :first-child)
• Pseudo-elements: (::before, ::after)

11. What is the DOM (Document Object Model)?

The DOM is a programming interface for web documents. It represents the structure of an HTML or XML document as a tree of nodes, each node representing a part of the document (elements, attributes, text, etc.).

12. What is the difference between JavaScript and Java?

JavaScript is a lightweight, interpreted programming language used for client-side scripting in web pages, whereas Java is a statically typed, compiled programming language used for building standalone applications and server-side applications.

13. What is AJAX and how does it work?

AJAX (Asynchronous JavaScript and XML) allows web pages to load content asynchronously without reloading the entire page. It uses the XMLHttpRequest object or the fetch API to send HTTP requests and update parts of the page dynamically.

14. What is the purpose of the var, let, and const keywords in JavaScript?

• var keyword has function scope (or global scope).
• let declare a block-scoped variable.
• const declares a block-scoped, read-only variable.

15. What is the difference between HTML and HTML5?

Here is the comparison between HTML and HTML5:

₹ 49,000

₹ 33,000

/-

Karthik was able to transform his career from a boring job to an exciting job in software!

Talk to a career expert

16. What is a Session in Web Applications?

A session in web applications refers to the way entities are interacted with and engaged during a shared period in time spanning multiple clicks or actions. In essence, a web application session forms a unique window of interaction with the application, where a user may be identified through unique credentials which may be collected and analyzed for user experience via analytics and recommendation systems. Sessions are a necessity for user verification, monitoring e-commerce activities such as add to cart or track items, and recording temporary settings selected by the user.

17. What is Hibernate and how it is used in database interaction?

Hibernate is an open-source Object-Relational Mapping (ORM) framework for Java. It simplifies database interactions by mapping Java objects to relational database tables and vice versa. Hibernate provides a way to interact with a database using high-level object-oriented code, rather than writing raw SQL queries. This results in easier maintenance, better portability, and a more flexible system.

18. What is dependency injection in spring?

Dependency Injection (DI) in Spring is a design pattern where Spring Framework automatically provides dependencies (objects or services) to a class, promoting loose coupling and easier testing by injecting them via constructors, setters, or fields.

19. What is the difference between GET and POST?

Here is the comparison of GET and POST:

20. How do you handle the load time of a web application?

• Optimize images and use proper formats.
• Implement caching to store frequently used data.
• Minimize HTTP requests and remove unnecessary plugins.
• Use a Content Delivery Network (CDN).
• Optimize JavaScript and CSS.

Experienced Java Full Stack Developer interview questions often cover a broad range of topics, assessing deep understanding and practical application across various layers of development.

21. What is the difference between Spring MVC and boot?

Here is the comparison of Spring MVC and Spring Boot:

22. What is the role of the @RestController annotation in Spring?

The @RestController annotation in Spring is used to define a controller that handles HTTP requests and returns responses directly to the client in the form of JSON or XML. It is a convenience annotation that combines @Controller and @ResponseBody to simplify RESTful web service development.

Benefits

• Simplifies REST API creation.
• Reduces the need for multiple annotations.
• Automatically serializes response to JSON or XML.

23. What is RESTful Web Services?

RESTful Web Services are web services based on REST (Representational State Transfer) principles, which use HTTP methods (GET, POST, PUT, DELETE) for communication between client and server. They are stateless, scalable, and cacheable, making them ideal for web and mobile applications.

24. What are WebSockets?

WebSockets function as a protocol which establishes continuous bidirectional interactions between client  devices and servers. WebSockets show uninterrupted real-time communication which surpasses standard HTTP request capabilities. Live  data update applications such as chat platforms and notification systems find WebSockets perfect for maintaining real-time information delivery.

25. What is the use of @Transactional annotation?

Spring utilizes the @Transactional annotation to establish  transaction borders. Spring validates execution of database operations within a single transaction for methods using the annotation which commits  or rolls back operations based on method success or failure.

26. Explain the difference between Session-based and Token-based authentication

27. What is Docker and its benefits?

Docker is a containerization platform that allows developers to package applications and their dependencies into containers. This makes it easier to deploy and run applications consistently across different environments. Docker enhances the development, testing, and deployment processes in full-stack development by providing an isolated, reproducible environment.

Benefits

• Simplifies deployment and management.
• Ensures consistency across development, staging, and production environments.
• Scalable and resource-efficient.

28. What is the Concept of Spring boot and how it is used for Java Applications

Spring Boot is a framework built on top of the Spring framework. It simplifies the development of production-ready applications by providing defaults for configurations, embedded servers (like Tomcat, and Jetty), and automatic dependency management. It reduces the need for complex configurations and helps in rapid development. Spring Boot allows you to create stand-alone applications that can run directly without an external servlet container.

29. How do you perform unit testing in Java using JUnit or TestNG?

JUnit and TestNG are popular testing frameworks in Java. Unit tests are written to test individual units of code, such as methods or classes. These tests check whether the code behaves as expected. You can use annotations like @Test in JUnit and @Test in TestNG to define test methods and assertions to verify results.

30. Explain the concept of a Promise in JavaScript.

A Promise represents the eventual completion (or failure) of an asynchronous operation. It has three states:

• Pending: The operation is still in progress.
• Fulfilled: The operation was completed successfully.
• Rejected: The operation failed.

To prove yourself during your Java Full Stack Developer job interview the following advice will prove helpful:  

• Be ready to discuss your system design methodology together with scalability and fault tolerance approaches along with performance optimization methods.
•  You need to master basic Java programming and Spring Boot framework and Hibernate ORM along with RESTful API development.
• You should understand the Full Stack Java Developer skill progression which defines essential abilities for front-end development together with back-end development and database management.
• Take a Full Stack Java Developer course to reinforce your knowledge and build a strong portfolio.
• Understand the Full Stack Java Developer roadmap will show you which abilities should be acquired for front-end development as well as back-end work and database management.
• You must be prepared to describe how you design systems while explaining your methods for achieving scalability and fault tolerance and performance optimization.

Java full stack developer interviews assess breadth across multiple technologies while testing depth in key areas like Java, Spring Boot, and front-end frameworks. Success requires both theoretical knowledge and practical experience building complete applications.

Final Preparation Checklist:

• Work on 2-3 comprehensive full stack projects demonstrating all the skills 
• Practice the explanation of the technical decisions and the trade-offs involved 
• Revise the Spring Boot annotations and their functions 
• Know the React component lifecycle and the hooks 
• Practice the activities of database design and query optimization 
• Get ready with system design examples for typical applications 
• Authenticate a security best practices 
• Gain knowledge of deployment and DevOps basics

Interview Day Tips: Solve the problem by thinking out loud to your interviewer which will help them trace your thought process. Before going to the solution, asking a clarifying question is always a good step. If you are not sure about the topic and have limited knowledge, be frank with the interviewer instead of trying to guess. If possible, link the answer with the real project that you have done. Enabling the learning process to work for you and showing it to the interviewer will definitely keep up the positive vibe.

Post-Interview: Send thank-you email within 24 hours. Reflect on questions you struggled with and study those topics. Continue building projects and learning even while interviewing. Every interview is learning experience improving future performance.

₹ 49,000

₹ 33,000

/-

Karthik was able to transform his career from a boring job to an exciting job in software!

Talk to a career expert

1. How should I prepare for a Full Stack Java Developer Interview?

To prepare effectively:

• Master Java, Spring Boot, and databases.
• Understand front-end technologies like Angular and React.
• Practice coding problems and system design concepts.

2. What are some common challenges faced by Java Full Stack Developers?

• Ensuring seamless communication between the front-end (JavaScript, Angular) and back-end (Java, Spring Boot).
• Designing applications that can scale efficiently as user traffic increases.
• Managing different versions of front-end and back-end technologies.
• Implementing secure APIs and protecting user data.

3. What are the skills of a Java Full-Stack Developer?

A Java Full Stack Developer should have:

• Understanding of core Java fundamentals and features introduced in Java 8 and later versions.
• Back-end development needs dependency on Spring Boot along with Hibernate.
• Front-end frameworks like Angular or React.
• Database skills include MySQL, PostgreSQL, MongoDB.
• The development of RESTful APIs requires integration skills.
• The developer must know how to use Git/GitHub for version control.
• Build tools are Maven or Gradle.
• Cloud basics (AWS, Azure, or GCP).
• The ability to solve problems and debug issues is essential.

4. How do you approach testing and debugging in Java Full Stack applications?

• Use JUnit/TestNG for unit testing Java code; Jest/React Testing Library for front-end.
• Use Postman for API testing, Node.js Inspector and browser developer tools for debugging.
• Apply error boundaries in React and error-handling middleware in Express.js.
• Profile performance with profiling tools and analyze server logs for issues.

5. How do you deploy and maintain Java Full Stack applications in production?

• Use CI/CD pipelines (GitHub Actions, Jenkins) for automated testing and deployment.
• Containerize applications with Docker for consistency.
• Use cloud services (AWS, Azure, MongoDB Atlas) for hosting and managed databases.
• Automate database migrations and dependency management with tools like Flyway and Maven/Gradle.
• Monitor for scalability and real-time updates.

6. What are the most important database management concepts for Java Full Stack Developers?

Java Full Stack Developers should be familiar with both SQL and NoSQL databases (such as MySQL, PostgreSQL, MongoDB, Redis). Key concepts include:

• SQL vs NoSQL: Understanding when to use structured tables (SQL) versus flexible schemas (NoSQL).
• Data modeling: Apply normalization to reduce redundancy and denormalization for performance.
• CRUD operations: Efficiently implement Create, Read, Update, and Delete.
• Database relationships: Use embedded documents and references in MongoDB with populate, and joins in SQL.
• Aggregation framework: Utilize the aggregation pipeline of MongoDB for analytical processes.
• Indexes: Build and maintain indexes for performance improvement of queries.
• Database migrations: Implement schema changes securely with the help of tools (such as Flyway or Liquibase).
• Write concern: Set up for reliability in distributed databases.
• Cloud integration: Make use of MongoDB Atlas to have an easily managed NoSQL solution.
• Caching: Integrate Redis for fast data access and session management.