Java Full-Stack Developer Interview Questions for 10+ years Experience

Java Full-Stack Developer Interview Questions for 10+ years Experience

On June 5, 2025, Posted by , In FullStack Developer,Interview Questions, With Comments Off on Java Full-Stack Developer Interview Questions for 10+ years Experience

Table Of Contents

As a Java Full-Stack Developer with 5 years of experience, you’re expected to master both front-end and back-end development while seamlessly integrating the two. Interviewers often dig deep into your expertise with Java frameworks like Spring Boot and Hibernate, as well as your ability to work with modern front-end technologies such as React or Angular. They’ll challenge you with scenario-based questions to gauge your problem-solving skills, test your understanding of REST APIs and microservices, and evaluate your knowledge of databases like MySQL or MongoDB. Additionally, they’ll likely explore your familiarity with DevOps practices, version control systems like Git, and your ability to optimize deployment pipelines.

In this guide, I’ve compiled a list of Java Full-Stack Developer interview questions tailored for professionals with 5 years of experience. These questions don’t just highlight key topics but also provide insights to tackle them confidently. Whether you’re preparing to ace technical rounds or want to refine your approach to solving real-world challenges, this content is designed to be your roadmap. With these resources, you’ll feel equipped to impress your interviewers and secure that next big opportunity in your career!

1. What are the core principles of Object-Oriented Programming (OOP)?

In my experience, the four core principles of Object-Oriented Programming (OOP) are Encapsulation, Inheritance, Polymorphism, and Abstraction. Encapsulation helps me group related data and methods into a single unit (a class) and control access using access modifiers like private or public. Inheritance allows me to reuse code by creating new classes that inherit properties and methods from existing ones, making my code more maintainable and organized.

Polymorphism enables me to use a single interface to represent different implementations, such as method overriding or overloading. Abstraction, on the other hand, helps me hide unnecessary details and focus only on essential features, often implemented using abstract classes or interfaces. For example, when creating a base class Animal with a method speak(), I can implement specific behaviors in subclasses like Dog and Cat.

abstract class Animal {
    abstract void speak();
}

class Dog extends Animal {
    void speak() {
        System.out.println("Bark");
    }
}

class Cat extends Animal {
    void speak() {
        System.out.println("Meow");
    }
}

Code Explanation:
The Animal class is declared abstract and contains an abstract method speak(). Subclasses Dog and Cat inherit from Animal and provide their specific implementations of speak(). This demonstrates abstraction (hiding the common functionality in Animal) and polymorphism (each subclass defines its behavior). The code allows calling speak() dynamically depending on the actual object type.

See also: Interview Tips for a Software Engineer Role

2. Explain the role of the Spring Framework in Java development.

From my perspective, the Spring Framework is essential in simplifying Java enterprise application development. It provides a comprehensive ecosystem with modules like Spring Core, Spring MVC, and Spring Data, which streamline complex tasks like dependency injection, web development, and database management. I often rely on its Inversion of Control (IoC) container to manage object creation and lifecycle, which reduces boilerplate code and increases testability.

Spring also enables seamless integration with various technologies and frameworks. For instance, its support for REST API development through @RestController and database operations using Spring Data JPA is remarkable. Here’s an example where I use Spring Boot to set up a REST API:

@RestController
@RequestMapping("/api")
public class MyController {
    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, Spring!";
    }
}

Code Explanation:
The @RestController annotation indicates that this class handles HTTP requests. The @RequestMapping("/api") maps the base URL, while @GetMapping("/hello") maps the GET request to the sayHello() method. When the API endpoint /api/hello is accessed, it returns the response "Hello, Spring!", showcasing how REST APIs can be implemented with minimal setup.

3. How does dependency injection work in Spring Boot?

In my experience, Dependency Injection (DI) is one of the most powerful features of Spring Boot. It allows me to inject required objects into a class, reducing tight coupling and making the application easier to test and maintain. Spring achieves DI using annotations like @Autowired, which automatically wires dependencies at runtime. For instance, instead of manually creating a service object, Spring injects it where needed.

I often use DI to manage services and repositories in my applications. For example, if I have a UserService class that depends on a UserRepository, Spring Boot handles the wiring automatically:

@Service
public class UserService {
    private final UserRepository userRepository;

    @Autowired
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User getUserById(Long id) {
        return userRepository.findById(id).orElse(null);
    }
}

Code Explanation:
The @Autowired annotation automatically injects an instance of UserRepository into the UserService class. The UserService constructor ensures that this dependency is initialized properly. This approach eliminates manual instantiation, enhances modularity, and makes the code easier to test and maintain.

See also: Python Full-Stack Developer Interview Questions

4. What is Hibernate, and how does it simplify database interactions?

In my experience, Hibernate is a powerful ORM (Object-Relational Mapping) tool that simplifies database interactions by mapping Java objects to database tables. This eliminates the need for complex SQL queries in most cases, as Hibernate uses methods like save() or find() to handle database operations. I often use it with Spring Boot to perform CRUD operations efficiently.

Hibernate also supports lazy and eager loading, caching, and automatic table creation based on entity classes. For instance, consider this entity class:

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    // Getters and setters
}

Code Explanation:
The @Entity annotation marks the User class as a database entity. The @Table(name = "users") specifies the corresponding table name. The @Id and @GeneratedValue annotations define the primary key and its auto-generation strategy. Hibernate uses this mapping to interact with the database without requiring explicit SQL statements.

5. What are the differences between ArrayList and LinkedList in Java?

In my experience, the main difference between ArrayList and LinkedList lies in their data storage and performance. ArrayList is backed by a dynamic array, which makes it faster for random access and retrieving elements. However, adding or removing elements, especially in the middle, can be slower due to shifting operations. I use ArrayList when I need quick access to elements by index.

On the other hand, LinkedList is a doubly-linked list, which makes it more efficient for inserting or deleting elements anywhere in the list. However, accessing elements by index is slower since it requires traversal from the beginning or end. Here’s a quick example:

List<String> arrayList = new ArrayList<>();
arrayList.add("A");
arrayList.add("B");

List<String> linkedList = new LinkedList<>();
linkedList.add("A");
linkedList.add("B");

Code Explanation:
In this example, ArrayList and LinkedList are initialized and populated with elements. Both collections implement the List interface, but their underlying implementations differ. ArrayList uses a dynamic array for quick indexing, while LinkedList uses nodes that allow efficient insertions and deletions. Understanding their performance characteristics helps me choose the right collection for specific use cases.

See also: Java Full-Stack Developer Interview Questions

6. Explain the concept of RESTful APIs and their key components.

In my experience, RESTful APIs (Representational State Transfer) are a popular architectural style for designing networked applications. They rely on stateless communication and HTTP methods (GET, POST, PUT, DELETE) to manage resources. RESTful APIs use URLs to represent resources, and the data is typically exchanged in formats like JSON or XML. The core principles of REST include statelessness, client-server architecture, and uniform interface, which make it highly scalable and easy to implement.

One key aspect of RESTful APIs is their use of HTTP methods to perform operations on resources. For example, a GET request retrieves data from the server, while a POST request creates new resources. Below is an example of a REST controller in Spring Boot:

@RestController
@RequestMapping("/api")
public class UserController {

    @GetMapping("/users/{id}")
    public User getUser(@PathVariable Long id) {
        return userService.findById(id);
    }
}

Code Explanation:
Here, the @GetMapping("/users/{id}") method handles a GET request to fetch a user by ID. The @PathVariable annotation binds the {id} from the URL to the method parameter. This simple setup shows how resources are accessed using HTTP methods, making RESTful APIs an efficient and flexible solution for web services.

7. How does Java handle memory management and garbage collection?

In my experience, Java handles memory management through an automatic process known as Garbage Collection (GC). The Java Virtual Machine (JVM) allocates memory for objects on the heap. Over time, when objects are no longer needed (i.e., they are unreachable), the garbage collector identifies and reclaims that memory, ensuring the program does not run out of memory.

The JVM uses several garbage collection algorithms, including Mark and Sweep, Generational Garbage Collection, and others. In real-world applications, I often observe that managing memory effectively can improve performance. Here’s an example of how memory management works in Java:

public class GarbageCollectionExample {
    public static void main(String[] args) {
        MyClass obj1 = new MyClass();
        obj1 = null;  // obj1 is now eligible for garbage collection
    }
}

class MyClass {
    // Some fields and methods
}

Code Explanation:
In this example, obj1 is assigned a new instance of MyClass, but then set to null, making it eligible for garbage collection. The garbage collector will eventually reclaim the memory used by the object since no other references exist for it. This illustrates the automatic memory management in Java.

See also: Collections in Java interview Questions

8. What is the significance of the @Entity annotation in Hibernate?

In my experience, the @Entity annotation in Hibernate is crucial because it marks a class as a persistent Java object, meaning it can be mapped to a database table. It tells Hibernate that the class should be stored in the database and that its instances are considered entities that can be queried, saved, or updated using Hibernate’s ORM features.

I often use the @Entity annotation to map Java classes to database tables and define the table structure with additional annotations like @Table, @Id, and @Column. For example:

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;
    
    // Getters and setters
}

Code Explanation:
The @Entity annotation tells Hibernate to treat the User class as a database entity. The @Id annotation defines the primary key, and @GeneratedValue specifies how the primary key is generated. The @Table(name = "users") annotation maps the class to the users table in the database, making it ready for persistence operations.

9. Can you explain the Model-View-Controller (MVC) architecture?

From my experience, the Model-View-Controller (MVC) architecture is a design pattern commonly used in web applications to separate concerns and improve maintainability. In MVC, the Model represents the data and business logic, the View is responsible for rendering the user interface, and the Controller handles user input and updates the model. This separation allows developers to work on each component independently.

I often use MVC in web applications to ensure that business logic (Model) and UI elements (View) are decoupled, which makes the code easier to maintain and scale. For example, in a Spring MVC-based application, you might define a controller like this:

@Controller
public class UserController {

    @GetMapping("/users/{id}")
    public String getUser(@PathVariable Long id, Model model) {
        User user = userService.findById(id);
        model.addAttribute("user", user);
        return "userView";
    }
}

Code Explanation:
Here, the UserController class handles the HTTP request with @GetMapping("/users/{id}") to fetch a user by ID. The Model object is used to pass data (the user object) to the view (userView). This shows how MVC helps organize the application by separating data handling, UI rendering, and user interactions.

See also: Accenture Java interview Questions

10. What is the purpose of the try-catch-finally block in Java?

In my experience, the try-catch-finally block in Java is used for exception handling. The try block contains code that may throw exceptions, while the catch block handles specific exceptions that arise. The finally block, if present, always executes regardless of whether an exception occurs, making it ideal for cleanup activities like closing files or releasing resources.

For example, I use it to handle database connections and ensure that resources are released properly:

public void readDataFromDatabase() {
    try {
        // Code that may throw an exception
        databaseConnection.connect();
    } catch (SQLException e) {
        System.out.println("Error: " + e.getMessage());
    } finally {
        databaseConnection.close();  // Ensures cleanup
    }
}

Code Explanation:
In this example, the try block attempts to connect to a database, while the catch block catches any SQLException that occurs. Regardless of whether an exception occurs, the finally block ensures that the database connection is closed, preventing resource leaks.

11. How do you define and handle exceptions in Java?

In my experience, exceptions in Java can be defined using the try-catch block, and custom exceptions can be created by extending the Exception class. I use exceptions to handle errors gracefully in my code, ensuring that they don’t crash the application. By catching exceptions, I can provide meaningful error messages or even recover from errors without terminating the program.

Here’s how I define a custom exception:

class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

Code Explanation:
In this example, I define a custom exception CustomException by extending the Exception class. The constructor takes a message, which is passed to the superclass constructor. This allows me to throw and catch custom exceptions, giving more context about the error that occurred.

See also: Advanced Senior Full-Stack Developer Interview Questions

12. What is the difference between HashMap and TreeMap?

In my experience, the primary difference between HashMap and TreeMap lies in the order of elements. HashMap does not maintain any specific order of elements, while TreeMap maintains a natural order (sorted by keys) or a custom order defined by a Comparator. Therefore, if I need a sorted map, I prefer TreeMap; otherwise, HashMap is faster and more efficient for simple key-value pair storage.

Here’s an example of both:

Map<Integer, String> hashMap = new HashMap<>();
hashMap.put(3, "Three");
hashMap.put(1, "One");

Map<Integer, String> treeMap = new TreeMap<>();
treeMap.put(3, "Three");
treeMap.put(1, "One");

Code Explanation:
In this example, the HashMap does not maintain any order, while the TreeMap sorts the keys automatically in ascending order. For instance, when iterating through the treeMap, it will display the elements as 1 -> One and 3 -> Three, which shows the automatic sorting feature of TreeMap.

13. What are the key differences between JDBC and Hibernate?

From my experience, the main differences between JDBC and Hibernate are in terms of complexity and abstraction. JDBC requires manual management of SQL queries, connection pooling, and result set processing, making it more cumbersome and error-prone. On the other hand, Hibernate abstracts much of this away by using ORM to map Java objects to database tables and handle queries automatically through HQL or Criteria API.

Hibernate also provides additional features like caching and lazy loading, which improve performance. For example:

Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
session.save(new User("John"));
transaction.commit();

Code Explanation:
In this example, Hibernate uses a session to manage transactions and automatically maps the User object to the database table. The simplicity of saving an object with just session.save() is a huge improvement over the manual SQL query approach with JDBC.

See also: Intermediate Senior Full-Stack Developer Interview Questions

14. Explain how sessions are managed in a web application.

In my experience, sessions in web applications are typically managed using a session ID, which is stored on the server side and sent to the client as a cookie or URL parameter. Each time a user makes a request, the session ID is sent back to the server, which retrieves the user’s session data. This allows the server to track the user’s state between requests.

For example, in a Spring MVC application, sessions are often used to store user data:

@RequestMapping("/login")
public String login(HttpSession session) {
    session.setAttribute("user", user);
    return "dashboard";
}

Code Explanation:
Here, the session stores the user object in the HttpSession. This session is then available for future requests, allowing the application to persist the user’s state without requiring them to log in again on each page.

15. What is a Singleton design pattern, and where would you use it?

In my experience, the Singleton design pattern ensures that a class has only one instance throughout the application’s lifetime. It is particularly useful when we need to control access to shared resources like database connections, configuration settings, or logging services.

I often use the Singleton pattern in scenarios where having multiple instances would lead to resource waste or conflicts. For example:

public class DatabaseConnection {
    private static DatabaseConnection instance;

    private DatabaseConnection() {}

    public static DatabaseConnection getInstance() {
        if (instance == null) {
            instance = new DatabaseConnection();
        }
        return instance;
    }
}

Code Explanation:
In this example, the DatabaseConnection class follows the Singleton pattern. The getInstance method ensures that only one instance of the DatabaseConnection class is created. If the instance is null, it creates one; otherwise, it returns the existing instance.

See also: Basic Senior Full-Stack Developer Interview Questions and Answers

16. How do you create a custom exception in Java?

In my experience, creating a custom exception in Java involves extending the Exception class or its subclasses, depending on whether you want the exception to be checked or unchecked. Custom exceptions allow you to define meaningful error messages and error-handling mechanisms specific to your application’s needs.

To create a custom exception, you can define a class that extends Exception or RuntimeException. For example:

class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

Code Explanation:
Here, CustomException extends Exception and takes a custom message, which is passed to the super constructor of the Exception class. This allows you to throw CustomException whenever a specific error condition occurs in your application. For example:

throw new CustomException("An error occurred!");

17. What is the difference between == and equals() in Java?

In my experience, the == operator in Java checks if two references point to the exact same memory location (i.e., whether they are the same object). On the other hand, the equals() method compares the content of two objects, determining whether their values are equivalent, rather than checking their memory addresses.

For example, consider the following code:

String str1 = new String("Hello");
String str2 = new String("Hello");

System.out.println(str1 == str2); // false
System.out.println(str1.equals(str2)); // true

Code Explanation:
In this example, str1 == str2 returns false because they are two different objects in memory. However, str1.equals(str2) returns true because both strings contain the same value (“Hello”). This shows how equals() compares the content of objects, while == compares their references.

See also: Top 50 Full Stack Developer Interview Questions 2025

18. What is Maven, and how does it help in project management?

In my experience, Maven is a build automation and dependency management tool used primarily in Java projects. It simplifies the process of compiling, testing, packaging, and deploying applications by managing dependencies and providing a structured approach to building projects.

Maven uses an XML configuration file called pom.xml to define project dependencies, plugins, and goals. For example, Maven automatically downloads the required dependencies from central repositories. Here’s an example of a pom.xml snippet:

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.2.7.RELEASE</version>
    </dependency>
</dependencies>

Code Explanation:
In this pom.xml file, Maven will automatically download the Spring Core library (version 5.2.7.RELEASE) from a central repository. This simplifies dependency management, ensuring that the required libraries are included in the project without manually downloading and managing them.

19. What are Java annotations, and why are they used?

In my experience, Java annotations are special markers that provide metadata about the code, but they do not directly affect the program’s behavior. Annotations are commonly used to provide additional information to compilers, tools, or frameworks.

For example, in Spring Framework, annotations like @Autowired and @Component are used to define beans and inject dependencies. Here’s an example:

@Component
public class MyService {

    @Autowired
    private MyRepository myRepository;
}

Code Explanation:
In this example, @Component marks MyService as a Spring-managed bean, while @Autowired tells Spring to inject an instance of MyRepository into MyService. Annotations like these make code easier to understand, and frameworks like Spring can automatically handle dependencies without additional configuration.

See also: Goldman Sachs Senior FullStack Engineer Interview Questions

20. How do you implement pagination in a database query?

In my experience, pagination in a database query is useful for fetching a specific subset of records, especially when dealing with large datasets. It can be implemented by using SQL’s LIMIT and OFFSET clauses (in SQL databases like MySQL or PostgreSQL) to specify which portion of the data to retrieve.

For example, in JPA (Java Persistence API), you can use the setFirstResult() and setMaxResults() methods to paginate queries:

public List<User> getUsers(int page, int size) {
    Query query = entityManager.createQuery("SELECT u FROM User u");
    query.setFirstResult((page - 1) * size); // OFFSET
    query.setMaxResults(size); // LIMIT
    return query.getResultList();
}

Code Explanation:
In this example, the setFirstResult() method sets the starting index for the records, and setMaxResults() limits the number of records to retrieve. This implementation helps in retrieving only a specific subset of data, which is especially useful for displaying results across multiple pages in user interfaces.

Advanced-Level Questions

21. What are the advantages of using microservices architecture in a full-stack application?

In my experience, microservices architecture offers several benefits when building a full-stack application. By breaking down a monolithic application into smaller, independently deployable services, microservices improve scalability, flexibility, and maintainability. Each service can be developed, deployed, and scaled independently, which helps teams work in parallel and deliver faster. Additionally, microservices enable you to use the best technology stack for each service, making the system more adaptable to future changes.

For example, in a full-stack application for e-commerce, you might have separate microservices for the product catalog, payment processing, and order management. These services can be scaled individually, depending on their load, and can evolve without affecting the other parts of the application. This separation allows for more efficient maintenance and updates, reducing the impact of changes on the overall system.

22. How do you implement caching in Spring Boot to improve application performance?

In my experience, caching in Spring Boot can significantly improve application performance by reducing the need for repeated database queries or expensive computations. Spring Boot supports caching using a variety of providers like EHCache, Redis, and Memcached. By enabling caching on specific methods or data, you can reduce load times and enhance responsiveness.

To implement caching in Spring Boot, I typically annotate methods with @Cacheable. For instance:

@Cacheable("products")
public List<Product> getProducts() {
    return productRepository.findAll();
}

Code Explanation:
In this example, the @Cacheable annotation caches the result of getProducts() method. The cache is identified by the “products” name, and subsequent calls to this method will return the cached result instead of querying the database again. You can configure a cache manager in your Spring configuration class to specify which cache provider (e.g., Redis) to use.

See also: Adobe FullStack Developer Interview Questions

23. Explain the concept of thread safety and how to achieve it in a multithreaded environment.

In my experience, thread safety refers to ensuring that a class or method behaves correctly when accessed by multiple threads concurrently. In a multithreaded environment, if multiple threads access and modify shared data without proper synchronization, it can lead to data corruption or unexpected behavior.

To achieve thread safety, I use techniques like synchronized blocks, locks, or atomic classes. For example, I might use a ReentrantLock for controlling access to shared resources:

ReentrantLock lock = new ReentrantLock();
lock.lock();
try {
    // critical section
} finally {
    lock.unlock();
}

Code Explanation:
In this example, ReentrantLock ensures that only one thread at a time can execute the critical section of code. The lock.lock() method acquires the lock, and lock.unlock() releases it. This guarantees that only one thread can modify shared data, ensuring thread safety in a multithreaded environment.

24. How do you secure REST APIs in Java using OAuth2 or JWT?

In my experience, securing REST APIs is crucial to protecting sensitive data and ensuring that only authorized users can access specific resources. OAuth2 and JWT (JSON Web Tokens) are two widely used mechanisms for API security. OAuth2 is an authorization framework that allows third-party services to access user data without exposing credentials. JWT, on the other hand, is used to transmit information between parties in a compact and secure way.

To implement OAuth2 with JWT in a Spring Boot application, I would configure a security filter chain and use the @EnableOAuth2Sso annotation. Here’s a simple example of using JWT for securing endpoints:

public class JwtAuthenticationFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
        String jwt = request.getHeader("Authorization");
        if (jwt != null) {
            // validate and parse the JWT token
        }
        filterChain.doFilter(request, response);
    }
}

Code Explanation:
In this example, the JwtAuthenticationFilter checks the Authorization header of incoming requests for a JWT token. If a token is present, the filter validates and parses it. This ensures that only valid tokens, which are usually generated after user login, are allowed access to secure endpoints.

See also: Full Stack developer Interview Questions

25. What strategies would you use to optimize database queries in a high-traffic application?

In my experience, optimizing database queries in high-traffic applications is essential to improving performance and scalability. Some common strategies include indexing, query optimization, and caching. Indexing improves the speed of query execution by creating data structures that allow fast retrieval of rows based on indexed columns. Additionally, I use pagination to limit the number of rows returned by each query, especially for large datasets.

For instance, I might optimize a query as follows:

SELECT * FROM users WHERE status = 'active' LIMIT 100 OFFSET 200;

Code Explanation:
In this example, the LIMIT and OFFSET clauses ensure that the query fetches only a specific subset of records, reducing the load on the database and speeding up the response time. Additionally, creating an index on the status column will speed up the search for active users by eliminating full-table scans. Combining these techniques ensures efficient data retrieval in high-traffic scenarios.

Scenario-Based Questions

26. You are tasked with designing a full-stack application for an e-commerce platform. How would you structure the application using Spring Boot and React?

In my experience, designing a full-stack e-commerce platform using Spring Boot for the backend and React for the frontend involves creating a modular architecture where each part of the application is independently deployable and maintainable. On the backend, I would use Spring Boot to handle business logic, data processing, and expose RESTful APIs to communicate with the frontend. For example, I might create controllers that return product data, manage user authentication, and process orders.

For the frontend, React is ideal for creating a responsive and dynamic user interface. I would structure the frontend into reusable components such as ProductList, ShoppingCart, and Checkout, each responsible for a part of the user experience. To connect the frontend and backend, I would use Axios or Fetch API to send HTTP requests to the Spring Boot server. This separation ensures clean architecture and scalability, as well as ease of maintenance.

Example Code (Backend):

@RestController
@RequestMapping("/api/products")
public class ProductController {
    @GetMapping
    public List<Product> getAllProducts() {
        // Logic to fetch products from the database
        return productService.getAllProducts();
    }
}

Example Code (Frontend):

import React, { useEffect, useState } from 'react';
import axios from 'axios';

const ProductList = () => {
    const [products, setProducts] = useState([]);

    useEffect(() => {
        axios.get('/api/products').then((response) => {
            setProducts(response.data);
        });
    }, []);

    return (
        <div>
            {products.map(product => (
                <div key={product.id}>{product.name}</div>
            ))}
        </div>
    );
};

export default ProductList;

Code Explanation:

  • The backend ProductController fetches products using a service layer. This endpoint /api/products can be consumed by the frontend.
  • On the frontend, ProductList fetches product data using Axios, and displays it dynamically in the UI. This decoupled architecture ensures flexibility and scalability.

See also: AngularJS Interview Questions for 7 years experience

27. How would you debug a slow-performing API endpoint in a Java-based microservices architecture?

When debugging a slow-performing API endpoint in a Java-based microservices architecture, I start by identifying the root cause of the issue. The first step is to use logging and metrics to gather data on how long each part of the request processing takes. Tools like Spring Boot Actuator can expose metrics such as request/response times, which help pinpoint where the delay is happening.

I would also use profiling tools like JProfiler or VisualVM to analyze memory usage, thread activity, and CPU utilization during API execution. If the issue is related to database access, I might check the queries for inefficiencies, such as missing indexes or poorly optimized joins. Additionally, caching mechanisms like Redis can be implemented to reduce the load on the database and improve response time.

Example Code (Enabling Actuator Metrics):

management.endpoints.web.exposure.include=*
management.endpoint.metrics.enabled=true

Example Code (Controller-Level Debugging):

@RestController
@RequestMapping("/api/orders")
public class OrderController {
    @GetMapping("/{id}")
    public Order getOrder(@PathVariable Long id) {
        long startTime = System.currentTimeMillis();
        Order order = orderService.getOrderById(id);
        long endTime = System.currentTimeMillis();
        System.out.println("Execution time: " + (endTime - startTime) + "ms");
        return order;
    }
}

Code Explanation:

  • Actuator Metrics: Provides system-level insights like API response times and resource usage.
  • Controller Logging: Tracks the execution time for specific endpoints, helping isolate slow-performing logic.

28. Your application’s front-end displays incorrect data due to inconsistent back-end responses. How would you resolve this issue?

In my experience, when the frontend displays incorrect data due to inconsistent back-end responses, I first ensure that both the backend and frontend are in sync regarding data structure and expected values. I would check the API response from the backend to ensure it is returning the expected data and format. If necessary, I would log the API responses to validate that they match the data that the frontend expects.

Next, I would inspect the API call in the frontend code. Using console logs or a tool like Postman, I would verify that the frontend is correctly handling the response. If there are any discrepancies in the way data is processed or displayed, I would correct them in the frontend components. Additionally, I would ensure proper error handling and validation are in place to handle unexpected responses gracefully.

Example Code (Backend Validation):

@RestController
@RequestMapping("/api/users")
public class UserController {
    @GetMapping("/{id}")
    public ResponseEntity<User> getUser(@PathVariable Long id) {
        Optional<User> user = userService.getUserById(id);
        if (user.isEmpty()) {
            return ResponseEntity.status(HttpStatus.NOT_FOUND).body(null);
        }
        return ResponseEntity.ok(user.get());
    }
}

Example Code (Frontend Error Handling):

const fetchUser = async (userId) => {
    try {
        const response = await axios.get(`/api/users/${userId}`);
        if (response.status === 200) {
            setUser(response.data);
        }
    } catch (error) {
        console.error("Error fetching user data:", error);
    }
};

Code Explanation:

  • On the backend, I use status codes like 404 to handle missing data and prevent invalid responses.
  • On the frontend, I handle errors gracefully using try-catch blocks, ensuring the app doesn’t crash due to unexpected data.

29. You need to integrate a third-party payment gateway into your full-stack application. How would you approach this integration?

When integrating a third-party payment gateway into a full-stack application, I start by reviewing the API documentation provided by the payment provider, such as Stripe or PayPal, to understand the required steps for integration. On the backend, I would create an API endpoint in Spring Boot to handle the communication with the payment gateway. This involves sending the payment details (e.g., amount, user credentials) securely to the provider and handling the response (e.g., payment success or failure).

In the frontend, I would integrate the payment gateway’s SDK or API to collect payment details from the user. This often involves using React components to securely gather the card information without storing sensitive data directly on the server. Once the payment is processed, I would return the result to the user and update the frontend with the transaction status. Ensuring secure communication via HTTPS and proper handling of sensitive data is crucial for a successful integration.

Example Code (Backend):

@RestController
@RequestMapping("/api/payments")
public class PaymentController {
    @PostMapping
    public PaymentResponse processPayment(@RequestBody PaymentRequest request) {
        return paymentGateway.processPayment(request); // External gateway integration
    }
}

Example Code (Frontend):

const handlePayment = async () => {
    try {
        const response = await axios.post('/api/payments', paymentDetails);
        console.log("Payment success:", response.data);
    } catch (error) {
        console.error("Payment failed:", error);
    }
};

Code Explanation:

  • The backend communicates with the payment gateway securely and returns a success or failure response.
  • The frontend calls the backend’s payment endpoint and updates the UI based on the payment status.

See also: Tesla Software QA Engineer Interview Questions

30. A production server is facing performance degradation. How would you identify and resolve the bottlenecks?

When facing performance degradation on a production server, I would start by gathering performance metrics using tools like Spring Boot Actuator or external tools like Prometheus and Grafana. I would monitor key metrics such as CPU usage, memory consumption, and response times for various services. This helps identify if the bottleneck is related to hardware resources, a specific microservice, or a database issue.

Once the bottleneck is identified, I would further investigate the root cause. For example, if it’s a database issue, I would check the query performance and ensure indexes are being used efficiently. If the bottleneck is in the application logic, I would review the code for inefficient algorithms, memory leaks, or blocking calls. To mitigate the issue, I would implement caching where appropriate, scale services horizontally, or optimize the code by refactoring slow parts. If necessary, I would also consider using load balancing and auto-scaling to distribute traffic more evenly across servers.

Example Code (Caching with Redis):

@Service
public class ProductService {
    @Cacheable("products")
    public List<Product> getAllProducts() {
        return productRepository.findAll(); // Avoid repeated database calls
    }
}

Example Code (Load Balancer Configuration):

server:
  port: 8080

spring:
  cloud:
    loadbalancer:
      enabled: true

Code Explanation:

  • Caching: Using @Cacheable improves performance by avoiding repetitive database queries.
  • Load Balancer: Distributes traffic across multiple instances of the application, reducing load on any single server.

Conclusion

As a Java Full-Stack Developer with 10+ years of experience, you are expected to have an in-depth understanding of both backend and frontend technologies, along with the ability to design, implement, and optimize complex systems. The interview questions provided here cover the essential frameworks like Spring Boot, Hibernate, and modern concepts such as microservices, API security, and database optimization. It’s not just about theoretical knowledge, but demonstrating your hands-on expertise in solving real-world problems. Whether it’s integrating third-party services, improving application performance, or building scalable solutions, this content equips you with the insights needed to tackle any challenge during your interview.

To truly stand out in interviews for a Java Full-Stack Developer role, you need to show that you can apply these advanced concepts with practical experience. Mastering these topics will not only prepare you to answer interview questions with confidence but will also position you as a top contender for high-level roles. This preparation ensures you’re ready to discuss everything from system architecture and design patterns to the nuances of security and performance. By diving deep into these areas, you’ll demonstrate that you are not only a developer but a well-rounded expert capable of driving innovative solutions.

← →
Comments are closed.