35 Interview questions to ask while hiring a software developer 

Do you know hiring a qualified software developer is essential for any firm, especially in today’s competitive tech industry? According to a report by Glassdoor, the average cost of hiring a new employee in the U.S. is over $4,000, and the process can take up to 52 days. Furthermore, a survey by CodinGame revealed that 61% of HR professionals find it challenging to identify suitable candidates due to a lack of necessary skills.

With the increasing demand for tech talent and the high stakes of making the wrong hire, it’s essential to ask the right questions during the interview process. This ensures that the candidate possesses the technical expertise, fits well within the company culture, and aligns with its long-term goals.

This blog will explore key interview questions to help HR and CXO leaders identify top-tier software developers who can drive their organizations forward.

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Why use skills assessments for assessing software developer candidates?

In software development, accurately assessing a candidate’s skills is vital for making informed hiring decisions. Skills assessments accurately measure a candidate’s technical abilities, ensuring they meet the required proficiency levels for the role.

Platforms like Testlify provide a range of assessments specifically designed to evaluate coding skills and other essential competencies. Using these assessments, employers can objectively verify a candidate’s knowledge and problem-solving capabilities, reducing the risk of hiring mismatches.

By integrating skills assessments into the hiring process, organizations can enhance the quality of their hires and ensure they bring on board developers who are well-equipped to contribute effectively from day one.

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When should you ask these questions in the hiring process?

Using Software Developer interview questions in the hiring process begins with inviting applicants to complete a skills assessment. This initial step ensures that candidates possess the necessary technical expertise before progressing. By leveraging platforms like Testlify, employers can efficiently evaluate coding skills and other relevant competencies early in the process, especially for specialized areas such as Magento development services.

Once the assessments are reviewed, shortlisted candidates can be invited for interviews. During these interviews, specific questions tailored to the role can be asked to gauge problem-solving abilities, cultural fit, and alignment with company values. This structured approach streamlines the hiring process, ensuring that only the most qualified and suitable candidates advance to the final stages.

General software developer interview questions to ask applicants

When interviewing software developers, it is crucial to evaluate their technical skills, problem-solving abilities, and understanding of key programming concepts. The questions cover object-oriented programming, software architecture, database management, and modern development practices. Each question includes expected answers and what to look for, providing clear benchmarks for evaluation.

These questions ensure that candidates not only possess theoretical knowledge but can also apply these concepts practically. This helps identify well-equipped developers to contribute effectively to your team, ensuring a successful hire.

1. Can you explain the difference between an abstract class and an interface?

Look for: Understanding of object-oriented principles, the ability to articulate differences, and knowledge of language-specific implementations.

What to Expect: An abstract class can have abstract and concrete methods, while an interface can only have abstract methods (in some languages like Java). Abstract classes can have member variables, whereas interfaces cannot.

2. What are the principles of SOLID?

Look for: Familiarity with design principles, ability to explain each principle, and practical examples.

What to Expect: SOLID stands for Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion principles, guidelines for designing maintainable and extendable software.

3. Explain the concept of a RESTful API.

Look for: Understanding of REST principles, the ability to describe HTTP methods, and examples of designing or using RESTful APIs.

What to Expect: RESTful APIs use HTTP methods like GET, POST, PUT, DELETE to perform CRUD operations. They are stateless and follow principles like resource identification through URLs, and self-descriptive messages.

4. What is a closure in JavaScript?

Look for: Clarity in explanation, understanding of lexical scoping, and practical examples.

What to Expect: A closure is a function that retains access to its lexical scope even when the function is executed outside that scope. It allows functions to have private variables.

5. Describe the MVC architecture.

Look for: Understanding of the separation of concerns, the ability to explain each component, and practical examples of using MVC.

What to Expect: MVC stands for Model-View-Controller. The Model handles data and business logic, the View manages information display, and the Controller handles user input and updates the Model and View accordingly.

6. What are microservices?

Look for: Understanding of the benefits of microservices, knowledge of inter-service communication, and practical implementation experiences.

What to Expect: Microservices architecture breaks down a large application into smaller, independent services that communicate over APIs. Each service is focused on a specific business function.

7. How does garbage collection work in Java?

Look for: Knowledge of memory management, understanding of garbage collection algorithms, and ability to troubleshoot memory issues.

What to Expect: Java’s garbage collector automatically deallocates memory by removing objects that are no longer reachable in the application. It uses algorithms like mark-and-sweep or generational collection.

8. What is polymorphism in object-oriented programming?

Look for: Clear explanation of polymorphism, examples of method overriding and overloading, and practical use cases.

What to Expect: Polymorphism allows objects to be treated as instances of their parent class rather than their actual class. It can be achieved through method overriding and method overloading.

9. Can you explain the concept of dependency injection?

Look for: Understanding of inversion of control, the ability to describe different types of dependency injection, and examples of using DI frameworks.

What to Expect: Dependency injection is a design pattern where an object receives its dependencies from an external source rather than creating them. It promotes loose coupling and easier testing.

10. What are the differences between SQL and NoSQL databases?

Look for: Knowledge of database types, understanding of use cases for each, and practical experiences.

What to Expect: SQL databases are relational and use structured query language for defining and manipulating data. NoSQL databases are non-relational, can store unstructured data, and are designed for horizontal scalability.

11. What is a deadlock in multithreading, and how can it be prevented?

Look for: Clear understanding of multithreading issues, ability to describe prevention techniques, and practical troubleshooting experiences.

What to Expect: A deadlock occurs when two or more threads are waiting indefinitely for resources held by each other. It can be prevented using techniques like resource ordering, lock timeout, and deadlock detection algorithms.

12. Explain the concept of a hash table.

Look for: Understanding of hash functions, collision handling techniques, and practical examples.

What to Expect: A hash table is a data structure that maps keys to values using a hash function. It provides an average time complexity of O(1) for lookups, insertions, and deletions.

13. What is a design pattern? Can you give an example of a commonly used design pattern?

Look for: Knowledge of various design patterns, ability to explain specific patterns, and practical implementation examples.

What to Expect: Design patterns are reusable solutions to common software design problems. An example is the Singleton pattern, which ensures a class has only one instance and provides a global point of access to it.

14. Describe the Agile methodology.

Look for: Understanding of Agile principles, familiarity with specific frameworks, and experiences with Agile practices.

What to Expect: Agile is an iterative approach to software development that emphasizes flexibility, customer feedback, and collaborative work. It includes frameworks like Scrum and Kanban.

15. What is the difference between a process and a thread?

Look for: Understanding of concurrency, ability to describe the relationship between processes and threads, and practical examples.

What to Expect: A process is an independent program in execution with its own memory space, while a thread is a smaller unit of a process that can run concurrently within the process’s memory space.

16. How do you optimize a SQL query?

Look for: Knowledge of SQL performance tuning techniques, ability to provide specific optimization strategies, and practical experiences.

What to Expect: SQL query optimization can be achieved through indexing, avoiding unnecessary columns in SELECT statements, using JOINs appropriately, and analyzing query execution plans.

17. What is the role of version control systems like Git in software development?

Look for: Understanding of version control concepts, familiarity with Git commands, and examples of using Git in projects.

What to Expect: Version control systems track changes to code, facilitate collaboration among developers, and help manage different versions of a project. Git allows for branching, merging, and maintaining a history of changes.

18. Explain the concept of event-driven programming.

Look for: Understanding of event handling, the ability to describe event loops and listeners, and practical examples.

What to Expect: Event-driven programming is a paradigm where the flow of the program is determined by events like user actions, sensor outputs, or messages from other programs. It is commonly used in GUI applications.

19. What is a monolithic architecture?

Look for: Understanding of monolithic vs. microservices architecture, ability to describe pros and cons, and practical experiences.

What to Expect: Monolithic architecture is a traditional software design where all components are integrated into a single, cohesive unit. It is simple to develop but can be difficult to scale and maintain.

20. Can you explain the concept of a binary search tree?

Look for: Understanding of tree structures, the ability to explain traversal methods, and practical examples.

What to Expect: A binary search tree is a data structure where each node has at most two children. It maintains a sorted order, with left child nodes containing values less than the parent and right child nodes containing values greater.

21. What is the purpose of unit testing?

Look for: Knowledge of testing principles, familiarity with testing frameworks, and practical examples of writing unit tests.

What to Expect: Unit testing involves testing individual components or functions of a software application to ensure they work correctly. It helps in identifying bugs early and facilitates refactoring.

22. Explain the difference between synchronous and asynchronous programming.

Look for: Understanding of concurrency, the ability to explain async/await or callback mechanisms, and practical examples.

What to Expect: Synchronous programming executes tasks sequentially, blocking subsequent tasks until the current one is completed. Asynchronous programming allows tasks to run concurrently, improving responsiveness.

23. What is a Docker container?

Look for: Knowledge of containerization, ability to describe Docker commands, and practical experiences.

What to Expect: A Docker container is a lightweight, portable unit of software that packages an application and its dependencies, allowing it to run consistently across different environments.

24. How do you handle exceptions in your code?

Look for: Understanding of error handling mechanisms, the ability to provide examples, and familiarity with best practices.

What to Expect: Exception handling involves using try-catch blocks to manage errors gracefully. It ensures that the program can recover from unexpected issues and continue running or terminate safely.

25. What is the purpose of a build tool like Maven or Gradle?

Look for: Knowledge of build automation, ability to describe tool-specific commands, and practical experiences.

What to Expect: Build tools to automate the process of compiling code, running tests, and packaging applications. They manage dependencies and ensure consistent builds across different environments.

Code-based software developer interview questions to ask applicants

Assessing a candidate’s practical coding skills through real-time problem-solving is essential. Here are five brief coding-level interview questions designed to evaluate key programming abilities quickly. Each question is structured to take a few minutes to complete, focusing on various fundamental aspects of coding. Additionally, a “Look For” section guides you on what to evaluate in their responses, ensuring you can accurately gauge their proficiency and approach to problem-solving.

26. Write a function to reverse a string.

Look for: Understanding of string manipulation, concise and correct implementation, and use of efficient methods.

def reverse_string(s):

    return s[::-1]

27. Write a SQL query to find the second highest salary from an Employee table.

Look for: Knowledge of SQL functions, ability to handle subqueries, and understanding of aggregate functions.

SELECT MAX(salary) FROM Employee WHERE salary < (SELECT MAX(salary) FROM Employee);

28. Write a function to check if a number is prime.

Look for: Understanding of basic algorithms, correct implementation of prime checking, and efficiency considerations.

def is_prime(n):

    if n <= 1:

        return False

    for i in range(2, int(n**0.5) + 1):

        if n % i == 0:

            return False

    return True

29. Write a function to merge two sorted arrays into one sorted array.

Look for: Understanding of array manipulation, ability to combine arrays, and efficient sorting.

def merge_sorted_arrays(arr1, arr2):

    return sorted(arr1 + arr2)

30. Write a function to find the factorial of a number using recursion.

Look for: Understanding of recursion, correct implementation, and handling of base cases.

def factorial(n):

    if n == 0:

        return 1

    else:

        return n * factorial(n - 1)

Interview questions to gauge a candidate’s experience level

31. Can you describe a time when you had to collaborate with a difficult team member? How did you handle the situation?

32. Tell me about a project you are particularly proud of. What was your role, and what was the outcome?

33. How do you prioritize and manage your tasks when faced with tight deadlines?

34. Describe a situation where you had to learn a new technology or tool quickly. How did you approach it?

35. How do you handle feedback and criticism of your work? Can you provide an example?

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Key takeaways 

In the software developer hiring process, it’s essential to combine technical assessments with strategic interview questions to ensure a comprehensive evaluation. Technical questions and coding tasks help gauge a candidate’s proficiency and problem-solving abilities, while skills assessments, like those provided by Testlify, offer objective measures of their coding expertise.

Understanding soft skills and past experiences through targeted questions also helps assess cultural fit and work style, ensuring the candidate aligns with the company’s values and can thrive in a collaborative environment.

Integrating these methods provides a balanced approach to hiring, ensuring that candidates have the necessary technical skills and possess the interpersonal abilities and work ethic to contribute positively to the team. This holistic evaluation process enhances the likelihood of successful hires who can drive the organization forward and adapt to its dynamic needs.

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