Top Java Interview Questions & Answers for 0-5 Years Experience | Part 1

1. Tell me about your experience and skills

Entry-Level: Highlight your academic projects, internships, and exposure to tools/technologies like Java, Spring Boot, Hibernate, REST APIs, and front-end frameworks like Angular/React. Focus on what you’ve learned and implemented.

"I worked on a project to develop a library management system using Spring Boot and Angular. My role involved building REST APIs for book management and user authentication."

Experienced: Talk about your hands-on experience with end-to-end development, deployments, and architectural design. Mention team management or problem-solving in live production.

"I have 5 years of experience in developing scalable microservices using Spring Boot and managing deployment pipelines with Jenkins and Docker."

2. Monolithic Vs Microservices

Monolithic:

• Single, large application where all modules are tightly coupled.
• Hard to scale and maintain.
• Example: A legacy e-commerce system where all functionalities (user management, orders, payments) are in a single codebase.

Microservices:

• Independent services handling specific functionalities.
• Easier to scale, deploy, and maintain.
• Example: Amazon’s system, where user management, payment, and recommendations are independent microservices.

3. What are the challenges you have seen in Microservices?

Common Challenges:

• Communication Issues: Services need proper mechanisms (e.g., REST, gRPC) for interaction.
• Data Consistency: Managing distributed transactions (use of tools like Saga).
• Deployment Complexity: Managing multiple services using orchestration tools (e.g., Kubernetes).
• Debugging: Difficult to trace errors across services.

4. How many Microservices have you developed?

Mention specific services and their functionalities.

"I developed 5 microservices for an e-commerce platform, handling user authentication, order management, inventory, payment, and notifications."

5. How do you make a call from one service to another?

There are two common methods:

• REST API: Use HTTP-based communication.
• Service Discovery: Use tools like Eureka or Consul for service lookup.

// Example using RestTemplate in Java
RestTemplate restTemplate = new RestTemplate();
String response = restTemplate.getForObject("http://service-b/api/data", String.class);
    

6. How do you specify the hostname in REST URL?

Use environment variables or configuration files.

// Example in Spring Boot
service.url=http://localhost:8080
    

7. What is Heartbeat?

A mechanism to check if a service is alive.

Example: Using Spring Actuator, a service can expose /actuator/health, which other services can ping to check the status.

8. How will you know the other service is up and running?

Use health-check endpoints or monitoring tools like Prometheus and Grafana.

// Example using RestTemplate
RestTemplate restTemplate = new RestTemplate();
String status = restTemplate.getForObject("http://service-b/actuator/health", String.class);
    

9. What is Service Discovery?

Automatically detects and registers services, avoiding hardcoding URLs.

Example: Netflix Eureka or Consul dynamically manage service registration.

10. What is Eureka Server?

A service registry by Netflix for service discovery.

Example: Service A can find Service B by querying Eureka Server.

11. Monitoring of Microservices: Which tools are you familiar with?

Entry-Level: Learn tools like Spring Boot Actuator, Postman, and basic logging.

Experienced:

• Prometheus + Grafana: For metrics and visualization.
• ELK Stack (Elasticsearch, Logstash, Kibana): For centralized logging.
• Zipkin/Jaeger: For distributed tracing.

Example Workflow: Use **Prometheus** to collect metrics and visualize them in **Grafana** dashboards. Set up alerts for critical thresholds.

12. Explain the Architecture of the Microservices.

Components:

• API Gateway: Routes requests to services (e.g., Zuul, Spring Cloud Gateway).
• Service Discovery: Registers and discovers services (e.g., Eureka).
• Database: Each service has its database for separation of concerns.
• Load Balancer: Ensures traffic distribution.
• Monitoring: Tracks service health and performance.

13. How is the request routed to Microservices?

Via API Gateway, which routes based on the URI.

Example: A user’s login request is routed to http://api-gateway/login.

14. Where is security validation handled?

Use API Gateway or Authentication Service.

Example: JWT token validation in Spring Boot:

@RequestMapping("/validate")
public boolean validateToken(String token) {
    return jwtService.validateToken(token);
}
    

15. What is Route Filtering?

Filters modify requests/responses in an API Gateway.

Example: Zuul filters for logging or adding headers.

16. Where does the control start in a Spring Boot application?

It starts in the main() method:

public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
}
    

17. What are the basic elements needed to start the Spring Boot application?

• @SpringBootApplication
• application.properties
• REST Controller for endpoints.

18. What are the main features of Spring Boot?

• Auto-configuration
• Embedded servers (e.g., Tomcat)
• Actuator for monitoring
• Dependency management with Spring Boot Starter.

19. Which version of Java have you worked on?

Highlight your expertise.

"I have worked on Java 8, 11, and 17, focusing on features like Streams and Records."

20. What are the main features of Java 8?

• Lambda Expressions: Simplify functional programming.

List names = Arrays.asList("Alice", "Bob");
names.forEach(System.out::println);
      

• Streams API: For bulk operations on data.
• Default Methods: In interfaces.
• Optional Class: Avoid NullPointerException.