Software Developer Interview Questions UK: 8 Real Questions and What Interviewers Want

Most Software Developer interviews in the UK follow a pattern, and knowing it beats guessing. Below are eight questions from our bank of 25, each with a note on what the interviewer is really after.

Eight Software Developer interview questions, and what the interviewer is thinking

1. What is dependency injection, and why would you use it in the code you write?

Why they ask: Interviewers use this to check you understand loose coupling and testability, not just framework features.

2. How does asynchronous programming work in the main language you use, and when would you choose it?

Why they ask: Most modern developer roles involve async code, and misunderstandings cause subtle performance bugs.

3. What does a typical day as a software developer involve for you?

Why they ask: They want to confirm your expectations match the reality of the job, including the non-coding parts.

4. Can you explain the difference between SQL and NoSQL databases and how you decide which to use?

Why they ask: This tests whether you choose data stores on evidence rather than fashion.

5. What is the N+1 query problem, and how would you spot and fix it?

Why they ask: It is one of the most common real performance faults in applications that use an ORM.

6. You are asked to fix a bug in a part of the codebase with no tests. How do you go about it?

Why they ask: This shows whether you can change code safely when the safety net is missing.

7. How do you design and version a REST API so that existing consumers are not broken by changes?

Why they ask: Breaking changes to APIs cause real incidents, so employers want developers who think about consumers.

8. Tell me about a time you tracked down a difficult bug in production.

Why they ask: This reveals your debugging method and how you behave under pressure.

A sample answer to question 1

What is dependency injection, and why would you use it in the code you write?

Dependency injection means a class receives the things it depends on from outside rather than creating them itself. Instead of an order service calling new on a payment client, the client is passed in through the constructor, usually as an interface. The big benefit is testability: in a unit test I can hand in a fake or mock payment client and check behaviour without touching a real gateway. It also makes swapping implementations easy, for example moving from one email provider to another, and it keeps classes focused on their own job. In .NET and Spring I'd rely on the built-in container and register services with sensible lifetimes, being careful that a singleton never captures a scoped dependency. I'd also avoid overusing it, because injecting ten dependencies into one class usually signals that the class is doing too much and needs splitting.

Common mistake to avoid: Describing a framework only with no principle; Ignoring constructor bloat as a design smell

Want the rest?

Full model answers, key points and common mistakes for all 25 questions are on the Software Developer interview questions page. The first five are free, no sign-up needed.