Software Engineer Interview Questions
In a software engineering interview, the main aim of the interviewer is to evaluate a candidate’s problem-solving skills, technical skills, and if they are a cultural fit. Candidates should look for opportunities to demonstrate their projects, capabilities, and previous contributions to the team. Before diving into the software engineering interview questions, let’s first understand what software engineering means.
What is Software Engineering?
Software engineering is the process of designing, creating, and maintaining computer applications. This process involves adherence to engineering principles, techniques, and practices. The main aim of software engineering is to improve quality and develop a reliable software product.
Top Software Engineering Interview Questions
Software engineering interview questions cover technical coding, algorithms, design and architecture, testing, quality assurance, and other concepts. The interview questions vary depending on the role. Candidates must be well-prepared, not only in technical concepts but also in problem-solving. Some top software engineering interview questions are below:
Software Engineering Interview Questions for Freshers
In a software engineering interview, freshers are asked about basic coding concepts, data structures and version control. They are also asked to showcase their personal projects and soft skills. The top 20 software engineering interview questions for freshers are:
1. What is Object-Oriented Programming (OOP)?
Interviewers expect the candidate to demonstrate their level of grasp of OOP principles as it is the fundamental knowledge for a software engineering role.
Sample answer: Object-Oriented Programming (OOP) is a programming approach that focuses on the concept of objects. An object combines data (attributes) and functions (methods) that operate on data to mimic real-world entities and relationships in code.
2. Explain the difference between a class and an object.
Hiring managers assess if the candidate can provide a clear explanation of technical concepts. The manager should evaluate accuracy, conceptual understanding, and communication skills.
Sample answer: A class outlines the structure and behavior of objects. On the other hand, an object is a specific instance created from a class and of the attributes and behavior defined in the class.
3. What are the four main principles of OOP?
When interviewers ask this question, they not only evaluate the candidate’s ability to explain the principles but also if they understand how these principles are used in software design and development. Candidates must use real-world scenarios and examples.
Sample answer: The four main principles of OOP are – encapsulation, inheritance, abstraction, and polymorphism. These principles help provide a structured approach to design modular, reusable, and manageable software.
4. What is the difference between a stack and a queue?
By asking this question, interviewers can measure a candidate’s critical thinking skills by noticing how the candidate is able to explain two concepts that are similar yet different. Interviewers must also assess the candidate’s eagerness to share their understanding.
Sample answer: A stack and a queue are two fundamental data structures used for organizing and managing elements. The main difference is that the stack follows a Last In, First Out order (LIFO), as in, the last element added is the first one to be removed. Queue follows a First In, First Out (FIFO) order where the element added first is removed first.
5. Describe the process of version control and its importance.
Hiring managers can determine how well the candidate is familiar with fundamental software development practices. The manager should observe if the candidate’s response indicates an understanding of why version control is essential.
Sample answer: Version control is a process that helps developers track and manage changes in their code. This system also keeps track of different versions, allowing developers to work on code and collaborate. Whenever a change is made, a ‘commit’ is created which describes the changes made. This record of changes helps developers in reverting back to previous versions, in case of errors. Also, multiple people can work without overwriting.
6. What is the difference between debugging and testing?
By asking this question, interviewers can measure how the candidate is able to differentiate the two concepts and explain their different purposes in the software development lifecycle.
Sample answer: Debugging is the process of identifying and fixing issues or bugs in the code. Testing, on the other hand, checks the code and ensures that it is working correctly.
7. Explain the concept of polymorphism in OOP.
When interviewers ask this question, they aim to measure if the interviewee has a solid grasp of the concept and its practical applications. The interviewers should expect an answer that displays a basic understanding of polymorphism and its usage in software development.
Sample answer: Polymorphism is a concept in OOP where distinct types of objects are treated as instances of a common class. It can be compared to having a base class with methods where subclasses implement them. This creates a more flexible and reusable code.
8. What is an API (Application Programming Interface)?
Interviewers expect the candidate to explain the role of API in software development and how well-versed they are in technical concepts.
Sample answer: API is like a set of rules that acts as a bridge between different software applications. It enables communication between them. Developers can use this to pre-build functions and services without needing to understand all the complex details.
9. How does a relational database differ from a NoSQL database?
Hiring managers should look for a clear and straightforward answer that demonstrates the candidate’s knowledge and enthusiasm. They should observe if the candidate can highlight the differences in terms of scalability, use cases, and data structure.
Sample answer: A relational database is organized into structured tables with predefined schemas. The data is stored in columns and rows, employing SQL for querying and data integrity. NoSQL are schema-less databases that use data models like document, graph, key value, and column-family.
10. What is the purpose of an HTTP request and response?
Hiring managers expect the candidate to understand the context of client-server interactions and provide examples of common use cases for HTTP requests and responses.
Sample answer: An HTTP request serves as a way for a client, like a web browser, to ask about something. It could be a webpage, a file, or submitting a form. HTTP response is the server’s reply to the request submitted by the client.
11. Explain the SOLID principles in software design.
By asking this question, interviewers can measure if the candidate is not only well-versed in certain principles but also apply them in real-life situations. Interviewers should expect practical examples of the same.
Sample answer: SOLID principles are a collection of guidelines in software to promote modular and maintainable code. For example, ‘S’ stands for Single Responsibility Principle, ‘O’ stands for Open/Closed principle, and so on. These principles help write code that’s easy to modify, extend, and collaborate.
12. What is the role of a software framework? Provide an example.
Interviewers should expect a specific and appropriate example of a software framework. This framework should simplify development and display their knowledge of common frameworks.
Sample answer: A software framework is a structured toolbox that contains pre-defined tools and components. It serves as a foundation for developing software applications and streamlining its development. For example, the Django framework is used for web development, and it includes features like ORM for database interaction and URL routing.
13. Describe the difference between procedural and object-oriented programming.
Hiring managers want to assess an interviewee’s analytical skills and the ability to explain each approach’s strengths and weaknesses. They should expect the candidate to apply theoretical knowledge to practical scenarios.
Sample answer: Procedural programming is like a sequential set of instructions where tasks are performed step-by-step. Problems are broken down into smaller tasks and certain functions are written to handle the same. OOP bundles data and functions together in objects, enabling code reusability.
14. What is a design pattern? Provide an example.
When interviewers ask this question, they seek to test whether the candidate has a grasp of software architecture and if they can apply it in practical scenarios. Interviewers must observe if the example provided is relevant to the common design problem.
Sample answer: A design pattern is a solution to recurring design problems. Developers use this to solve common challenges in a structured way. For example, the Singleton pattern can be used to create a class with just one instance across an application. It can be used to control access to a shared resource.
15. Explain the concept of multithreading and its advantages.
The interviewer determines if the candidate can explain the benefits of using multithreading in software development. Interviewers should also look out for the candidate’s appreciation for its advantages.
Sample answer: Multithreading is a concept where a single process is used to execute multiple threads at the same time. Threads are small, separate paths of execution within a program. The advantage of multithreading is that it enhances performance via parallel processing, making programs run faster.
16. What is the significance of Big O notation in algorithms?
The hiring manager assesses whether the candidate has a solid grasp of the fundamental concept behind Big O notation and the importance of algorithm efficiency. The managers should look for answers that are clear and simple to understand.
Sample answer: Big O notation is a tool used to measure algorithm efficiency. It helps understand the quantifiable relationship between the execution time or resource usage and the size of its input. This is significant because it allows for comparison between different algorithms to choose the one that performs best.
17. How does garbage collection work in programming languages?
Interviewers measure the candidate’s knowledge that goes beyond specific programming languages. They expect the candidate to articulate the general principles of garbage collection across multiple languages.
Sample answer: Garbage collection is a mechanism that automatically identifies, and releases memory no longer needed by the program. This prevents any leaks in memory and improves memory management.
18. What is a RESTful API?
The interviewer should determine the candidate’s familiarity with REST and its principles. They should expect the ideal answer that mentions the commonly used HTTP verbs and their actions in the context of RESTful APIs.
Sample answer: A RESTful API is a bridge between different software applications, allowing easy communication with each other over the internet. It uses HTTP methods like GET, POST, PUT, and DELETE to perform actions represented by URLs. It follows the principles of REST for easy interaction with data and services. Data is commonly exchanged in JSON or XML formats.
19. Discuss the importance of code documentation and comments.
Interviewers aim to measure the candidate’s understanding of the long-term value that clear and well-structured documentation brings to a software project. They should also look for professionalism, teamwork, and the ability to produce functional, comprehensible code.
Sample answer: Code documentation and comments explain what the code does and its working. Developers use this information to understand, revisit, and maintain code in the future. It’s basically writing instructions someone can follow.
20. How do you handle exceptions in your code?
The hiring manager gauges if the interviewee understands how exceptions occur during program execution. They should look for answers that explain different types of errors and mention try-catch blocks.
Sample answer: To handle this, I make use of ‘try’ and ‘catch’ blocks. I place the risky code inside the try block and specify the error-handling logic in the catch block. This ensures smooth execution of the program regardless of unexpected issues.
Software Engineering Interview Questions for Experienced
Technical Questions
Technical interview questions in a software engineering interview include topics like data structures, algorithms, string manipulation, coding challenges, OOP, system design, and other concepts. The top technical software engineering interview questions are:
1. Explain Object-Oriented Programming (OOP) concepts and give examples of each.
The interview determines if the candidate is able to discuss such concepts and how they are used to structure code and solve real-world problems. Interviewers should analyze if the candidate can provide relatable examples.
Sample answer: Encapsulation involves bundling data and methods. For example, in ‘car’ class, we can encapsulate an attribute like ‘speed’ and method like ‘accelerate.’ Inheritance allows a class to inherit attributes and methods from another class. Example, ‘cat’ class can inherit from a general ‘animal’ class. Abstraction focuses on showing complex entities as simplified models. For e.g., ‘employee’ class abstracts intricacies of various job roles. Polymorphism enables objects of different classes to be treated as those of a common superclass. Example, a ‘vehicle’ superclass with subclasses like ‘car’ and ‘bike’ each implement a ‘startEngine’ method differently.
2. Describe the differences between a thread and a process. When would you use one over the other?
When hiring managers ask this question, they expect the candidate to analyze scenarios and present the appropriate use case for threads and processes. Interviewers should look out for prior knowledge or experience related to this concept, which is a positive indicator.
Sample answer: A process is a standalone program that runs on its own memory and resources. It is heavier and is commonly used to isolate tasks. On the other hand, a thread is a smaller unit within a process that shares the same memory with other threads. It is lighter and more efficient. I would use processes when I want to isolate tasks completely and threads when I need to perform multiple tasks at the same time.
3. What is the SOLID principle, and how does it help in software design?
Hiring managers seek to measure how well the interviewee understands the influence of the SOLID principle on quality, maintainability, and scalability of systems. Managers should look for examples that explain how the violation of this principle affects the codebase.
Sample answer: The SOLID principle is a basic concept that focuses on creating easy, maintainable, and flexible code. Each letter in SOLID stands for a specific principle. Violation of any principle may lead to a class that’s harder to maintain, a fragile system, unexpected behavior, increased complexity, and changes all through the codebase.
4. Explain the difference between a linked list and an array. When would you choose one over the other?
When hiring managers ask this question, they assess the interviewee’s ability to make informed decisions based on trade-offs along with their understanding of data structures.
Sample answer: A linked list is a data structure where each element contains both the reference and data to the next element. An array is a collection of elements stored in sequential memory locations. A linked list can be used for its flexible memory allocation and dynamic sizing. Arrays are preferable when constant-time access to elements is needed.
5. Implement a function to reverse a string in place.
Interviewers ask this question to evaluate the interviewee’s thought process and code readability. Interviewers should look for the candidate’s ability to optimize their solution and their approach to solving a common coding problem.
Sample answer: I would use a two-pointer technique. I would initialize one pointer at the start of the string and the other at the end of the string. Then, I would switch the characters at these pointers and move them until they meet in the middle. By doing this, the string will be reversed in place.
6. Discuss the advantages and disadvantages of using a relational database vs. a NoSQL database for a specific use case.
By asking this question, interviewers expect the candidate to provide an answer that incorporates relational databases and NoSQL databases, including the differences and use cases.
Sample answer: A relational database fits scenarios where data relationships are defined, and transactions are crucial. They face challenges when it comes to scalability and the amount of data. In contrast, NoSQL databases offer adaptability to data. They can be used in use cases that demand quick and horizontal scalability.
7. Write code to find if a binary tree is a binary search tree (BST).
Interviewers should expect an accurate and efficient solution. It should be well-structured with relevant use of data structures and algorithms.
Sample answer: I would use an in-order traversal approach. During this approach, I will keep track of the previously visited node’s value. If the current node’s value is more than the previous node’s value, it is a BST.
8. Explain the concept of design patterns. Provide an example of a creational, structural, and behavioral design pattern.
When managers ask such a question, they aim to assess a candidate’s ability to explain design patterns without oversimplifying. They should look for the candidate’s problem-solving skills, analytical thinking, and potential to apply these patterns in future projects.
Sample answer: Design patterns are standardized solutions for commonly occurring issues in software design. For example – creational design patterns concentrate on the creation of objects, structural design patterns on the composition of objects and classes, and behavioral patterns on managing object interactions.
System Design Questions
1. Design a URL shortening service like bit.ly. Discuss the components and the technologies you would use.
Hiring managers are looking for candidates who can make informed technology decisions. Interviewers should observe how well the candidate can discuss the key components of the URL shortening service. An ideal answer would also include tracking CTR and user behavior.
Sample answer: Creating a URL shortening service needs system components and technologies. We would need a URL shortener, a database, and a web server. Scalability can be achieved by introducing load balancing. Also, for the database, I would choose a NoSQL solution like MongoDB for its scaling capabilities.
2. Architect a scalable system for a real-time chat application. What technologies and protocols would you use?
When interviewers ask this question, they are looking for a candidate who takes a thoughtful approach towards designing complex systems.
Sample answer: I would use a microservices-based architecture to architect a real-time chat application. For backend services, I would use technologies like Node.js, WebSockets, and OAuth 2.0. For data storage, I would choose a combination of relational and a NoSQL database like MongoDB. Content Delivery Networks (CNDs) can be used for quick content delivery.
3. Explain how you would design a caching system for a web application to improve performance.
By asking this question, hiring managers aim to measure the candidate’s technical knowledge, critical-thinking skills, and problem solving. Managers should look for an answer that mentions the specific needs of the web application.
Sample answer: Efficient caching system enhances performance via storage of frequently accessed data locally. This minimizes the load on the server. Strategies such as page caching and object caching can be used to store HTML pages and caching specific data.
4. Discuss the challenges and considerations when designing a distributed microservices architecture.
Interviewers are seeking both architectural and technical aspects of software development. They expect the candidate to think critically about potential issues and complex systems.
Sample answer: Designing a distributed microservices architecture shows both opportunities and challenges. A few challenges and considerations would be data consistency, scalability, fault tolerance, and communication between services.
Coding and Problem-Solving Questions
1. Given an array of integers, write a function to find the two numbers that add up to a specific target.
Hiring managers expect the candidate to showcase proficiency in programming fundamentals and an approach to handling data manipulation.
Sample answer: I would loop through the array. For every element, I would check if the difference between the current element and the target sum exists in the array. If it exists, I can identify the indices of the two numbers that sum up to the target and the return them.
2. Implement a LRU (Least Recently Used) cache.
Interviewers assess the candidate’s choice of data structure, coding logic, and error handling. Candidates need to discuss the main operations involved along with their purposes.
Sample answer: An LRU is like a storage mechanism for a limited number of items. It removes the least recently used item when the storage is full. To implement an LRU cache, I would use a design that includes a hash map and doubly linked list for quick access and usage management.
3. Write a function to determine if a string has balanced parentheses.
Hiring managers put forward this question to assess the candidate’s algorithm accuracy and efficiency. They check whether the candidate is able to handle all types of parentheses and if they provide comments to explain their logic.
Sample answer: I would take an iterative approach. If I identify an open parenthesis, I will push them onto a stack. If I identify a closed parenthesis, I will check the stack. The string can be deemed unbalanced if the stack is empty or the top element does not match the opening parenthesis.
4. Implement a function to find the longest common subsequence between two strings.
Interviewers are primarily looking for an interviewee’s capability to comprehend and apply data structures. Candidates must code with variable naming and comments to explain specific parts.
Sample answer: My approach would involve dynamic programming. I’ll create a 2D table where columns represent the second string’s characters, and the rows represent the first string’s characters. I would then fill the table by comparing characters. When there’s a match, I’ll add a value in the previous column and row. If they don’t, I’ll remove the highest value above and to the left. The value in the last cell will represent the length of the longest common subsequences between two strings.
5. Given a sorted array, write a function to create a balanced binary search tree (BST).
Interviewers are looking for a function that creates a balanced BST while also maintaining appropriate memory allocation.
Sample answer: I would divide the sorted array into 2 halves. The middle element would become the root of the current subtree. The function will look like the following in Python programming language:
def sorted_array_to_bst(nums):
if not nums:
return None
mid = len(nums) // 2
root = TreeNode(nums[mid])
root.left = sorted_array_to_bst(nums[:mid])
root.right = sorted_array_to_bst(nums[mid+1:])
return root
Behavioral and Soft Skills Questions
1. Describe a challenging technical problem you faced and how you approached solving it.
This question helps interviewers measure if the candidate can collaborate well with others, their overall attitude when facing challenges, and the ability to solve a technical problem.
Sample answer: During a software development project, there was a challenge involving a memory leak. It impacted the application’s stability and performance. I treated it as a priority and leveraged debugging tools and performance monitoring. I reviewed the section of the code and made necessary corrections in the missing deallocations.
2. Discuss a situation where you had to collaborate with a difficult team member. How did you handle it?
Hiring managers will be able to assess the candidate’s communication style and how they handle conflicts. Interviewers should observe if the candidate was able to achieve productive outcomes in the same scenario.
Sample answer: I faced a situation where a team member frequently missed deadlines and wasn’t open to feedback. I scheduled a private discussion with the person and focused on building rapport and discussing challenges. I was able to identify some personal challenges that were affecting their performance. We set realistic deadlines together and I provided them with any additional support. Ultimately, the team member could reach their deadlines and meet his performance goals.
3. Explain a project where you had to make significant trade-offs between different technical or business considerations.
By asking this question, interviewers can understand if the candidate can assess priorities and explain their reasons. They should evaluate the candidate’s thought process and decision-making ability.
Sample answer: In my previous company, our team was tasked with a mobile app development for a local business. The main challenge was to balance prompt delivery and additional features. We implemented advanced features like real-time location tracking, and so on. We prioritized timely deployment, considering their requirement for an online presence.
How can interviewers prepare for a software engineering interview
An interviewer’s role is to not only evaluate technical skills but also to look for candidates who will be a good fit for the company in terms of culture and values. The interviewer can prepare by:
- Researching the company’s Tech Stack: HR should learn about the technologies and frameworks used in the company. This will help them determine if the candidate is familiar with the same.
- Understanding the job description: Interviewers should understand the role’s responsibilities, experience, and skills required. This will help frame questions. They should also understand the technical skills required, programming languages’ level of proficiency, and technologies.
- Preparing technical and scenario-based questions: Once the job description has been understood, interviewers can collaborate with the technical team to prepare a list of technical questions. These questions should also be scenario-based to assess decision-making skills and communication skills.
- Listing down the follow-up questions: When preparing the above questions, be ready to follow up with another question to further understand the candidate’s response. This will encourage the candidate to elaborate.
- Planning the overall interview structure: Include technical assessments, coding challenges, and behavioral questions as necessary. Decide how much time should be allocated to each section and prepare a structure for the interview.
Red flags to watch for in candidates
Interviewers should always look out for potential red flags in a candidate that indicate that they are not suitable for the role or the company’s culture. The red flags to watch out for are:
- Poor technical knowledge
- The candidate doesn’t express curiosity
- No consideration of alternatives
- The candidate becomes defensive and argumentative when faced with criticism
- No interest in learning new tools
- Consistent coding errors
