Java Full Stack Interview Questions

Introduction to Java Full Stack Development

A Java Full Stack professional is a versatile software engineer who handles both frontend and backend development using Java-based technologies. This role requires expertise across the entire software development stack, including:

Backend Development: Core Java, Spring Framework, Hibernate/JPA, RESTful services
Frontend Development: HTML, CSS, JavaScript, and frameworks like Angular or React
Database Management: SQL/NoSQL database design and interaction
DevOps Practices: Containerization, CI/CD, cloud deployment
Software Architecture: Design patterns, microservices, distributed systems

Java Full Stack Developers are highly valued for their ability to implement entire features independently, understand system architecture holistically, and communicate effectively across different technical domains. They typically work with technologies like Spring Boot for backend services, modern JavaScript frameworks for responsive frontends, and tools like Maven or Gradle for build automation.

Youtub Playlist - Full Stack Java Developer Course

Core Java Fundamentals

Object-Oriented Programming

What are the four main principles of OOP, and how are they implemented in Java?
What is the difference between an interface and an abstract class?
Explain the concept of method overloading and overriding.
What is encapsulation and how is it implemented in Java?
What are access modifiers in Java and what do they do?
What is the difference between composition and inheritance?
Explain the concept of polymorphism with examples.
What is a marker interface in Java?
What is the purpose of the 'final' keyword when applied to classes, methods, and variables?
How does Java achieve multiple inheritance using interfaces?

Java Memory Management

Explain the difference between stack and heap memory in Java.
What is garbage collection in Java and how does it work?
What are strong, weak, soft, and phantom references in Java?
How can memory leaks occur in Java applications?
What is the difference between 'shallow copy' and 'deep copy'?

Java Collections Framework

Explain the difference between ArrayList and LinkedList.
What is the difference between HashMap and HashTable?
What are the differences between Set, List, and Map interfaces?
Explain the ConcurrentHashMap class and its advantages.
What is the difference between fail-fast and fail-safe iterators?
How does HashMap work internally in Java?
What is the difference between TreeSet and HashSet?
When would you use CopyOnWriteArrayList?
Explain the difference between Comparable and Comparator interfaces.
What is the purpose of the Collections.unmodifiableList() method?

Exception Handling

What is the difference between checked and unchecked exceptions?
Explain the try-with-resources statement.
What is the purpose of the finally block?
Can you have a try block without a catch block?
What is the difference between throw and throws keywords?
Explain the exception hierarchy in Java.
How would you create a custom exception in Java?
What is exception chaining?
What happens when an exception is not caught?
How does exception handling affect performance?

Multithreading & Concurrency

What is the difference between process and thread?
Explain the difference between synchronized method and synchronized block.
What are volatile variables in Java?
Explain the wait(), notify(), and notifyAll() methods.
What is the ExecutorService in Java?
What is thread safety and how do you achieve it?
Explain the difference between Runnable and Callable interfaces.
What is a deadlock and how can it be prevented?
What is a race condition and how can it be avoided?
What is the purpose of the java.util.concurrent package?
Explain the AtomicInteger and other atomic classes.
What is a ThreadLocal and when would you use it?
What is the ForkJoinPool and when would you use it?
How does the CountDownLatch work?
What is the difference between CyclicBarrier and CountDownLatch?

Java 8+ Features

What are lambda expressions and how are they used?
Explain the Stream API and its benefits.
What are default methods in interfaces?
What is the Optional class and why is it used?
What are the major new features in Java 9, 10, 11, and beyond?
Explain the difference between map() and flatMap() in Stream API.
What are method references in Java 8?
How does the CompletableFuture class work?
What is the purpose of the new Date and Time API in Java 8?
What are the advantages of the Collectors class in Stream API?
What are sealed classes in Java (introduced in Java 17)?
What are records in Java and what problem do they solve?
Explain pattern matching for instanceof in recent Java versions.
What are Text Blocks in Java and how do they improve code readability?
What is the var keyword introduced in Java 10?

Spring Framework

Spring Core

What is Inversion of Control (IoC) and Dependency Injection?
What are the different types of dependency injection?
Explain the difference between BeanFactory and ApplicationContext.
What are the different bean scopes in Spring?
What is AOP (Aspect-Oriented Programming) in Spring?
What is the bean lifecycle in Spring?
How do you handle circular dependencies in Spring?
What is Spring Expression Language (SpEL)?
Explain the difference between @Component, @Bean, and @Configuration.
What is the difference between constructor injection and setter injection?
How does @Autowired work under the hood?
What is the difference between @Qualifier and @Primary annotations?
What is the Spring ApplicationContext event system?
How do you create a custom scope in Spring?
What is lazy initialization of beans and when would you use it?

Spring MVC

Explain the MVC architecture in Spring.
What is the DispatcherServlet and what is its role?
What are the differences between @RequestParam and @PathVariable?
Explain the difference between @Component, @Service, @Repository, and @Controller.
What is Spring Boot and how does it simplify application development?
How does Spring MVC handle exceptions?
What is the @ModelAttribute annotation and how is it used?
Explain the concept of view resolvers in Spring MVC.
What is the purpose of the @ResponseBody annotation?
How does form validation work in Spring MVC?
What is Spring WebFlux and how does it differ from Spring MVC?
Explain the use of interceptors in Spring MVC.
What is the difference between @RestController and @Controller?
How do you handle file uploads in Spring MVC?
What is the purpose of the @InitBinder annotation?

Spring Data

What is Spring Data JPA?
Explain the difference between CrudRepository and JpaRepository.
What are derived query methods in Spring Data?
How does Spring Data handle transactions?
What is the @Query annotation and when would you use it?
How does Spring Data implement pagination?
What is the difference between JPQL and native SQL queries in Spring Data?
Explain the different transaction propagation levels in Spring.
What is the difference between @Transactional in service and repository layers?
How does Spring Data handle optimistic locking?
What is the EntityManager in JPA and how does Spring Data use it?
How would you implement a custom repository in Spring Data?
What is the use of Specifications in Spring Data JPA?
How do you handle database migrations with Spring applications?
Explain the difference between eager and lazy fetching in JPA.

Spring Security

What is Spring Security and what are its main features?
Explain authentication and authorization in Spring Security.
What is the SecurityFilterChain in Spring Security?
How do you implement method-level security in Spring?
What is the difference between authentication and authorization?
Explain the OAuth2 flow in Spring Security.
How does Spring Security handle password encoding?
What is Cross-Site Request Forgery (CSRF) and how does Spring Security prevent it?
How would you implement remember-me functionality in Spring Security?
What is the difference between Form Login and Basic Authentication?
How can you customize the authentication process in Spring Security?
What is JWT authentication and how is it implemented with Spring Security?
How do you test secured endpoints in Spring applications?
What is the UserDetailsService interface and how is it used?
How would you implement role-based access control in Spring Security?

Frontend Technologies

HTML/CSS

What is the difference between HTML and HTML5?
Explain the box model in CSS.
What are CSS preprocessors and what advantages do they offer?
What is responsive web design and how is it implemented?
What are semantic HTML elements and why are they important?
Explain the difference between inline, block, and inline-block display types.
What is the purpose of the meta viewport tag?
What are CSS media queries and how are they used?
Explain the difference between relative, absolute, and fixed positioning.
What is the CSS Flexbox layout and when would you use it?
What is CSS Grid and how does it differ from Flexbox?
What are CSS custom properties (variables) and how are they used?
How does browser rendering work (critical rendering path)?
What are pseudo-classes and pseudo-elements in CSS?
What is the purpose of normalize.css or reset.css?

JavaScript

What is the difference between var, let, and const?
Explain closure in JavaScript.
What is the event loop in JavaScript?
What are Promises and how do they work?
Explain the async/await syntax.
What is the difference between and = operators?
What is hoisting in JavaScript?
Explain prototypal inheritance in JavaScript.
What is the this keyword in JavaScript and how does it work?
What are arrow functions and how do they differ from regular functions?
What is event bubbling and event capturing?
How does the module system work in JavaScript?
What are Map and Set objects and when would you use them?
Explain the concept of memoization in JavaScript.
What is the difference between shallow and deep copying objects?
What are Web Workers and when would you use them?
What is the Fetch API and how does it differ from XMLHttpRequest?
Explain the concept of currying in JavaScript.
What is the purpose of the bind, call, and apply methods?
How does garbage collection work in JavaScript?

TypeScript

What is TypeScript and what are its advantages over JavaScript?
Explain interfaces in TypeScript.
What are generics in TypeScript?
What is the difference between interfaces and types in TypeScript?
How does TypeScript enhance object-oriented programming?
What are decorators in TypeScript and how are they used?
Explain the concept of namespaces in TypeScript.
What are enums in TypeScript?
How do you handle asynchronous operations in TypeScript?
What are declaration files (.d.ts) and what is their purpose?
What is the 'unknown' type in TypeScript and how does it differ from 'any'?
How does type inference work in TypeScript?
What are intersection types and union types?
Explain conditional types in TypeScript.
How do you implement mixins in TypeScript?

Angular

What is Angular and what are its key features?
Explain the component lifecycle hooks in Angular.
What is Angular dependency injection?
Explain the difference between template-driven and reactive forms.
What are Angular services and how are they used?
What is Angular CLI and what are its key commands?
What are directives in Angular and what are the different types?
How does change detection work in Angular?
What is Angular Router and how is it used for navigation?
Explain the difference between ngOnInit and constructor.
What are Angular pipes and how are they used?
What are Angular modules and what is their purpose?
What is lazy loading in Angular and how is it implemented?
How do you handle HTTP requests in Angular?
What is the purpose of the async pipe?
How do you optimize performance in Angular applications?
What is Angular Universal and what problem does it solve?
How does Angular handle state management?
What are route guards in Angular and when would you use them?
How do you test Angular components and services?

React

What is React and what are its key features?
Explain the component lifecycle in React.
What are React hooks and how are they used?
Explain the difference between state and props.
What is Redux and when would you use it?
What is JSX and how does it work?
How does Virtual DOM work in React?
What is the difference between class components and functional components?
Explain the concept of lifting state up in React.
What are controlled and uncontrolled components?
What is the Context API and when would you use it?
How do you optimize performance in React applications?
What are Higher-Order Components (HOCs) and what are they used for?
Explain the useEffect hook and its dependencies array.
What is the purpose of keys in React lists?
How does routing work in React applications?
What are React error boundaries?
How do you handle forms in React?
What is server-side rendering in React and why is it useful?
How do you test React components?

React Js Roadmap & Resources

Database Technologies

SQL

What is normalization and what are the normal forms?
Explain the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
What are transactions and the ACID properties?
What is an index and how does it improve performance?
What is the difference between a clustered and non-clustered index?
What are stored procedures and what are their advantages?
Explain the difference between DELETE, TRUNCATE, and DROP commands.
What is a view in SQL and when would you use it?
What is a subquery and what are its types?
What is a CTE (Common Table Expression) and when would you use it?
Explain the concept of database sharding.
What is a database trigger and when would you use it?
How does concurrency control work in relational databases?
What is a foreign key constraint and why is it important?
What is the difference between WHERE and HAVING clauses?

NoSQL

What are the different types of NoSQL databases?
When would you choose NoSQL over SQL databases?
Explain CAP theorem.
What is eventual consistency in NoSQL databases?
How does MongoDB store data?
What is the difference between MongoDB and Cassandra?
What are the advantages and disadvantages of document stores?
What is denormalization in NoSQL and why is it used?
How does indexing work in MongoDB?
What are the scalability features of NoSQL databases?
How do you handle relationships in document databases?
What is Redis and what are its use cases?
Explain the concept of BASE properties in NoSQL.
What is the aggregation framework in MongoDB?
What are the challenges of using NoSQL databases?

JPA/Hibernate

What is JPA and how does it relate to Hibernate?
Explain the difference between eager and lazy loading.
What are the different types of entity relationships in JPA?
What is the difference between get() and load() methods in Hibernate?
What is the Hibernate session and how does it work?
Explain the different states of an entity in Hibernate.
What is the first-level cache in Hibernate?
What is the difference between HQL and Criteria API?
What is object-relational impedance mismatch?
How do you map inheritance hierarchies in Hibernate?
What is the N+1 select problem and how can it be avoided?
Explain the Hibernate flush modes.
What is the difference between merge() and update() methods?
How does Hibernate handle database connection pooling?
What are entity listeners in JPA?

DevOps & Tools

Build Tools

What is Maven and how does it work?
Explain the difference between Maven and Gradle.
What is the purpose of the pom.xml file?
What is the Maven build lifecycle?
How do you manage dependencies in Maven?
What is a Maven plugin and what are some common plugins?
What is the difference between Maven parent pom and BOM?
How do you create a multi-module project in Maven?
What are Maven profiles and when would you use them?
How do you version your artifacts in Maven?

Version Control

What is Git and what are its advantages?
Explain the Git workflow with feature branches.
What is the difference between git merge and git rebase?
What is a Git hook and what are some common uses?
How do you resolve merge conflicts in Git?
What is Git cherry-pick and when would you use it?
Explain the concept of Git bisect.
What is the difference between Git pull and Git fetch?
How do you revert changes in Git?
What is Git stash and when would you use it?

Containerization

What is Docker and how does it work?
Explain the difference between Docker images and containers.
What is Docker Compose and when would you use it?
What is a Dockerfile and what are common instructions?
How do you manage persistent data in Docker?
What is Docker networking and what are the different network types?
What is the difference between Docker and virtual machines?
How do you optimize Docker images for size and security?
What is Kubernetes and how does it relate to Docker?
Explain the Docker container lifecycle.

Continuous Integration/Continuous Deployment

What is CI/CD and what are its benefits?
Explain the typical CI/CD pipeline for a Java application.
What tools are commonly used for CI/CD?
What is the difference between continuous delivery and continuous deployment?
How do you implement automated testing in a CI/CD pipeline?
What is infrastructure as code and how does it relate to CI/CD?
What are the best practices for CI/CD pipelines?
How do you handle database migrations in a CI/CD environment?
What is blue-green deployment and what are its advantages?
How do you implement security testing in a CI/CD pipeline?

Testing

What is the difference between unit, integration, and functional testing?
What is TDD (Test-Driven Development)?
What is JUnit and how is it used?
What is Mockito and when would you use it?
How do you test Spring Boot applications?
What is the difference between stubbing and mocking?
What is code coverage and how do you measure it?
What is BDD (Behavior-Driven Development)?
How do you write effective unit tests?
What is the pyramid of testing and why is it important?
What are some common testing patterns?
How do you write tests for asynchronous code?
What is the difference between black-box and white-box testing?
What tools would you use for performance testing?
How do you test RESTful APIs?

System Design & Architecture

RESTful Services

What is REST and what are the principles of RESTful API design?
Explain the difference between SOAP and REST.
What is microservices architecture and what are its advantages?
What is API Gateway and what problems does it solve?
Explain the concept of eventual consistency.
What is HATEOAS and why is it important for RESTful services?
What are the common HTTP status codes and their meanings?
How do you version RESTful APIs?
What is the difference between PUT and PATCH HTTP methods?
How do you handle authentication in RESTful services?
What is the OpenAPI Specification (Swagger) and how is it used?
How do you document RESTful APIs?
What is content negotiation in RESTful services?
How do you handle pagination in RESTful APIs?
What are idempotent operations and why are they important?

Architectural Patterns

What is CQRS (Command Query Responsibility Segregation)?
What are design patterns and why are they important?
Explain some common design patterns used in Java applications.
What is the difference between architectural patterns and design patterns?
Explain the MVC, MVP, and MVVM architectural patterns.
What is the Repository pattern and why is it useful?
What is the Circuit Breaker pattern and when would you use it?
Explain the Saga pattern for distributed transactions.
What is the Event Sourcing pattern?
What is the Strangler pattern and when would you use it?
What is the Bulkhead pattern in microservices?
Explain the Adapter pattern with a real-world example.
What is the Strategy pattern and when would you use it?
What is the Observer pattern and how is it implemented?
What is the Factory Method pattern and what problem does it solve?

System Design Roadmp & Interview Questions

Distributed Systems

What is service discovery and why is it important?
How would you implement inter-service communication in microservices?
What are the challenges of distributed systems?
How do you handle distributed transactions?
What is the CAP theorem and how does it apply to distributed databases?
What is a message queue and when would you use it?
Explain the Leader Election pattern in distributed systems.
What is the difference between synchronous and asynchronous communication?
How do you handle failures in distributed systems?
What is distributed tracing and why is it important?
What is the difference between vertical and horizontal scaling?
How do you ensure data consistency in a distributed environment?
What is Eureka in Spring Cloud and what problem does it solve?
How does load balancing work in a distributed system?
What is the role of a service mesh in microservices architecture?

Performance & Best Practices

What are some common performance issues in Java applications and how to address them?
How would you optimize a slow-performing Spring Boot application?
What are some best practices for securing a Java web application?
What is the Java Memory Model and why is it important?
Explain the different types of garbage collectors in Java.
What are the key metrics to monitor in a production Java application?
How do you identify memory leaks in Java applications?
What are the best practices for RESTful API design?
How do you handle connection pooling in database applications?
What is the role of caching in improving application performance?
How do you optimize database queries?
What are the best practices for logging in production applications?
How do you handle error tracking and monitoring in production?
What are the principles of clean code?
How do you ensure code quality in a team environment?