HCL Java Fullstack Developer Interview Experience & Questions

Summary

In this video, Faras Ahmed shares his successful Java Developer interview experience at HCL, including details about the technical and HR rounds. The technical interview covered key topics such as Spring Framework (Controller vs. RestController), immutability, thread safety, serialization, and the Singleton pattern. The interviewer also asked about design principles like SOLID, as well as core Java concepts like HashCode/Equals contract, collections, and indexing. Additionally, Faras discusses how to prepare for such interviews with a comprehensive Interview Preparation Kit that covers Java, Spring, Maven, Microservices, and more. A great resource for those preparing for similar interviews!

Takeaways

• 😀 Faras Ahmed successfully cracked the Java Developer interview at HCL with 3+ years of experience, applying via LinkedIn.
• 😀 The interview consisted of two rounds: a technical round (50 minutes) and an HR/Managerial round (30 minutes).
• 😀 Key technical topics covered include the differences between @Controller and @RestController in Spring, and how to return data (JSON, String) using these annotations.
• 😀 The interviewer emphasized understanding the hashcode-equals contract and its importance in Java collections like HashMap and HashSet.
• 😀 An important question focused on the consequences of a hash function always returning the same value (leading to performance issues with hash collisions).
• 😀 The Spring @Value annotation was discussed for injecting configuration values from properties files into Spring beans.
• 😀 Questions were asked about the use of the @Qualifier annotation in Spring to manage dependency injection when multiple beans exist.
• 😀 Faras was asked to explain how to design immutable classes in Java, emphasizing final fields, constructors, and avoiding setters.
• 😀 The interview covered SOLID principles, focusing on designing maintainable code, especially the Open/Closed Principle and Dependency Inversion.
• 😀 Common data structure questions included the differences between ArrayList and LinkedList, and how to choose one over the other based on use case.
• 😀 The importance of exception handling in Spring Boot was discussed, with solutions like @ControllerAdvice for handling global exceptions.
• 😀 The interviewer tested knowledge on thread safety and Singleton pattern implementation, including strategies for ensuring a logger remains a singleton in multi-threaded applications.

Q & A

What is the difference between a Controller and a RestController in Spring?

In Spring, a 'Controller' is used to return views like HTML pages, while a 'RestController' is used to return data in formats like JSON or XML. A RestController is a combination of the Controller and ResponseBody annotations, which sends a direct response body, skipping the view resolution step.

How can a Spring Controller return JSON data?

A Spring Controller can return JSON data by using the @ResponseBody annotation on the method. This tells Spring to return the method's return value as a direct JSON response, rather than trying to resolve it as a view.

What happens if you return a plain string from a Controller without using @ResponseBody?

If a Controller returns a plain string without the @ResponseBody annotation, Spring treats the string as a view name and tries to find a view (like a JSP or HTML page) with that name. This could cause unintended results, as it does not send the string as a direct response.

What does the 'hashCode equals contract' mean in Java, and why is it important?

The 'hashCode equals contract' in Java means that if two objects are considered equal (using the equals method), they must also have the same hash code. This is important for collections like HashMap and HashSet, which rely on the hash code and equals method to correctly store and retrieve objects.

What happens if the hash function always returns the same value?

If the hash function always returns the same value, all entries in the collection will go into the same bucket, causing many collisions. This results in slower performance as the collection uses a linked list or tree to store the items in that bucket, making access slower over time.

How does the @Value annotation work in Spring Boot?

In Spring Boot, the @Value annotation is used to inject values from application.properties or application.yml into fields in your Spring beans. It reads the value associated with the specified property and assigns it to the field annotated with @Value.

What is the purpose of the @Qualifier annotation in Spring?

The @Qualifier annotation is used in Spring to specify which bean should be injected when there are multiple beans of the same type. It is often used alongside the @Autowired annotation to ensure that the correct bean is chosen.

What is the difference between abstraction and encapsulation in object-oriented programming?

Abstraction focuses on hiding complex implementation details and exposing only the necessary functionality, essentially answering 'what' an object does. Encapsulation, on the other hand, bundles data and methods into a single unit and restricts access to certain parts of the object, focusing on 'how' the data is managed.

How can you ensure that a logger remains a singleton in a multi-threaded application?

To ensure that a logger is a singleton in a multi-threaded application, you can use a thread-safe singleton pattern. This can be achieved by synchronizing the method that provides the instance, or by using double-checked locking with a volatile instance to prevent multiple threads from creating separate instances.

How can global exceptions be handled in a Spring Boot application?

In Spring Boot, global exceptions can be handled by using the @ControllerAdvice annotation. This allows you to define a class where you can write methods annotated with @ExceptionHandler to handle specific exceptions globally across the application.