Senior Java Software Engineer Common Interview Questions

I have been living and working in the United Kingdom since 2019. I have been working with Java development since 2008 and here I will share some of the questions that have been recurring in the selection processes for senior positions. I recently went through a layoff process at a company and in the last 2 and a half months (taking into account the date of this article on June 5, 2024) I have carried out different types of interviews for the role of senior developer using the Java language.

Here I will share some of the recurring questions and the respective answers that you can provide in a concise and direct way, without beating around the bush or trying to invent them. Remember that some answers need to be deepened to explain more clearly to the interviewer, which means that the answers contained here are just suggestions for direct answers.

Of course, I was asked other questions, but the idea is to leave here the ones that I noticed are the most recurrent. From time to time I will add other questions and their direct answers as I notice new recurrences.

What is Object-Oriented Programming?

Object-oriented programming (OOP) is a way of organizing code by thinking about the objects in your program. These objects represent real-world entities and are used to encapsulate data and behaviour together. OOP principles include encapsulation, inheritance, polymorphism, and abstraction, which help create modular and reusable code.

What is Dependency Injection?

Dependency Injection (DI) is a design pattern in software engineering where the dependencies of a component are injected into it from the outside rather than being created within the component itself. This means instead of a component creating its own dependencies, they are provided to it from an external source. The main advantages of DI include increased modularity, easier testing, and better separation of concerns.

What Are The Advantages of Dependency Injection?

• Reduces coupling between components.
• Enhances code maintainability and testability.
• Promotes cleaner code and design.

What Are The Most Common Ways of Implementing Dependency Injection?

1. Constructor Injection: Dependencies are provided through a class constructor.
2. Setter Injection: Dependencies are provided through setter methods.
3. Method Injection: Dependencies are provided through methods.

What is a Deadlock?

A deadlock occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. This creates a circular waiting condition, leading to a standstill.

How to Avoid Deadlocks?

• Banker’s Algorithm: Processes declare the maximum resources they will use, and execution is allowed if the requested resources are less than available.
• Semaphores: Ensure mutual exclusion by allowing only one process in the critical section at a time.
• Mutual Exclusion: This condition states that at least one resource must be held in a non-sharable mode. It’s not always possible to eliminate this condition as some resources, such as printers or tape drives, are inherently non-shareable

What is Fault Tolerance?

Fault tolerance is the ability of a system to continue operating properly even if some of its components fail. It ensures system reliability and availability by handling failures gracefully.

What is a Circuit Breaker?

A circuit breaker is like a safety switch that automatically turns off the electricity if there’s too much current, preventing electrical fires and protecting appliances. In software, a circuit breaker pattern stops the flow of requests to a failing service, allowing the system to recover.

SQL vs NoSQL

When to Use SQL:

• Structured Data: When data has a well-defined structure and clear relationships.
• Complex Transactions: When ACID transactions are required to ensure data integrity.

When to Use NoSQL:

• Horizontal Scalability: When scalability is a priority, NoSQL is more flexible.
• Semi-structured/Unstructured Data: For data that doesn’t fit well into a relational model, like JSON or XML.

What’s the Difference Between Authentication and Authorization?

• Authentication: Verifying the identity of a user, typically through credentials like passwords, biometrics, or security tokens.
• Authorization: Determining whether an authenticated user has permission to access specific resources or perform certain actions.

What is REST?

REST (Representational State Transfer) is a system design that uses HTTP protocols for communication between distributed systems using HTTP methods.

What’s the Difference Between Abstract Class and Interface?

• Abstract Class: A partially defined class that cannot be instantiated. It can have both abstract and concrete methods, as well as instance variables.
• Interface: A completely abstract structure that only contains method signatures and constant fields.

What is the difference between the equals() and hashCode() methods in Java?

• equals(): Determines if two objects are logically equivalent.
• hashCode(): Provides a hash value for the object. Both must be overridden together to ensure proper behaviour in hash-based collections like HashMap and HashSet.

What’s the Difference Between ArrayList and LinkedList?

• ArrayList: Array-based implementation with fast random access but slow insertion/removal.
• LinkedList: Node-based implementation with slow random access but fast insertion/removal at any position.

What’s the Difference Between Checked and Unchecked Exceptions?

• Checked Exceptions: Checked at compile-time, requiring explicit handling or declaration.
• Unchecked Exceptions (RuntimeExceptions): Occurs during runtime, allowing the program to compile without explicit handling.

How to Handle Concurrency in Java?

Concurrency in Java can be handled using multithreading with the Thread class or Runnable interface, and controlling access to shared resources using synchronization mechanisms like synchronized blocks, volatile variables, or classes from the java.util.concurrent package.

How to Monitor Bugs in Production?

• Logging: Using Log4J, for example.
• Log Management: Using tools like Logstash or Datadog.
• Application Health Check: Using Spring Actuator for example
• Kubernetes: Using liveness and readiness probes.

How Does It Work The Garbage Collector in Java?

The Garbage Collector automatically manages memory by identifying and deallocating objects no longer in use, thus freeing up memory and preventing memory leaks.

How do you maintain the quality of your code?

1. Code Review: I regularly review my code to ensure it is clear and easy to understand. This includes checking variable names, comments, and the overall structure of the code.
2. Automated Testing: I use unit and integration tests to ensure my code works as expected and to prevent regressions when I make changes.
3. Refactoring: I regularly refactor my code to improve its structure and readability without changing its external behaviour.
4. Coding Standards: I follow consistent coding standards to ensure my code is easy to read and maintain.
5. Documentation: I document my code so that other developers can easily understand what it does and how to use it.
6. IDE Plugins and Tools: I use plugins and tools such as SonarLint, and CheckStyle, among others, which help me write more concise and clean code.

Can you tell me a little about SOLID principles?

• Single Responsibility Principle (SRP): A class should have only one reason to change.
• Open/Closed Principle (OCP): Software entities should be open for extension but closed for modification.
• Liskov Substitution Principle (LSP): Objects of a superclass should be replaceable with objects of a subclass without affecting the correctness of the program.
• Interface Segregation Principle (ISP): Clients should not be forced to depend on interfaces they do not use.
• Dependency Inversion Principle (DIP): High-level modules should not depend on low-level modules; both should depend on abstractions.

Conclusion

This article provides a comprehensive overview of common interview questions for senior Java software engineers, reflecting the author’s experience in the field. It covers essential topics like object-oriented programming, dependency injection, concurrency, and SOLID principles, offering concise and direct answers to help candidates prepare effectively. Additionally, it addresses practical concerns such as fault tolerance, SQL vs NoSQL, and methods for maintaining code quality. By sharing these insights, the article aims to equip senior Java developers with the knowledge needed to excel in interviews and advance their careers.

Remember as said at the beginning, the idea is that from time to time this article will be updated with more questions as they are recurrently reported during the interview processes.

Good luck in your future interviews ;)