I’ve conducted my share of interviews over the years. Early on, I didn’t have much of a strategy for interviewing candidates. Interviewing without a strategy didn’t work out too well for me, though. On a few occasions I recommended a candidate only to find out after working with them for a little while that they were not really as good a fit for the position as I had originally anticipated.
So, based on my past failures I have devised an interview strategy that I think works pretty well for me today. Apologies ahead-of-time for those of you non-computer peoples who may have inadvertently stumbled into this post. I am a computer software developer, and a lot of my strategy revolves around interviewing candidates for software development positions.
High level strategy
My interviews all use the following basic outline:
- Introduce myself – This includes a brief overview of my own employment history, followed by a short description of my current duties and responsibilities. (about 5 minutes)
- Ask questions of the candidate – This is the real meat of the interview, and where I plan to spend the most time. (as much time as I have available)
- Allow the candidate to ask me questions – I try to be as open and candid as possible. If I tell them something that scares them away, then perhaps they weren’t right for the job to begin with. (allow about 10 minutes at the end of the interview)
I’m very interested in a candidate’s goals. If my organization is going to invest time in training a new hire, I don’t want it to be someone who sees the job as a temporary stepping-stone to a different position.
Where do you see yourself in 5 years?
No, nothing ground-breaking here. It’s a pretty standard interview question, and yet it’s funny how many people are unprepared to answer this one. I may follow up with:
- What will you be doing in 5 years?
- What will be different from today?
- How about 10 years?
What kind of developer are you?
This is a multiple-choice question. I once heard (or read, I don’t remember which) that all developers fall into one (or some combination) of four categories. The four categories are:
- Clock puncher – This person is a competent, professional developer. They show up every day, sit at their computer, produce code, and go home at the end of the day. They receive a paycheck that adequately compensates them for their contribution, and they look forward to the day when they retire.
- Ladder climber – This person is also very competent and professional. They perform their duties diligently and to the best of their ability, frequently going above-and-beyond expectations. They have a constant eye to the next step. What’s after software development? Team lead? MBA? Program manager? Development manger? Higher?
- Artisan – This person sees software development as an art form. They look at an empty screen as a blank canvas on which to craft their masterpiece. Every function and every class must conform to some internal aesthetic that they have developed over years of study and practice. They will repeatedly refactor the same section of code until they are satisfied. They will post up their favorite creations to forums of like-minded individuals for others to “ooh” and “ahh” over.
- Scientist – This person is motivated by the problem. Each feature they work on is a puzzle to be solved, and this is their driving factor. The software is simply a means to a solution.
There really isn’t a wrong answer to this question. All roles are actually useful parts of a well-rounded development team. In fact, they are roughly analogous to the more detailed Belbin team roles.
I consider a firm grounding in theoretical software development practices to be very important. Good software development principles and practices are universal, and apply to almost every software language in existence. A strong theoretical understanding is what allows the good developers to learn new languages and technologies.
To get a general idea of a candidate’s knowledge of design patterns, I will usually open up the discussion with:
What design patterns have you used?
The answer to this question quickly and efficiently addresses a whole host of other questions:
- Are you familiar with the concept of design patterns?
- What patterns do you know about?
- Do you know how and when to apply them?
Assuming that their answer is acceptable, I will usually follow up on one or more of their responses to get more details:
- When did you use this pattern?
- Why did you select this pattern?
- What other patterns did you consider?
What, in your opinion, is the most important purpose for design patterns?
This is sort of a trick question. I ask them “in your opinion,” but I already have the “correct” answer to the question in mind. The most important purpose for design patterns is to assist in communication. I don’t even consider this debatable.
According to Wikipedia:
The usefulness of speaking of patterns is to have a common terminology for discussing the situations designers already see over and over.
The venerable Gang of Four book states in the introduction:
The pattern name is a handle we can use to describe a design problem, its solutions, and consequences in a word or two. Naming a pattern immediately increases our design vocabulary.
To date, no candidate has answered this question 100% correctly to my satisfaction, and I’ve asked it many times. Is it a useless question then? I don’t think so. How the candidate tackles the question is useful.
Bonus question: What’s the difference between applying design patterns vs. applying the DRY principle?
These questions focus on the concepts behind how languages work.
What is your favorite programming language?
I want to drive this next section of the interview towards a language that the candidate feels comfortable with. Followups include:
- What do you like about this language?
- What don’t you like?
- Compare / contrast with <some other language from their resume>
I usually skip this part of the interview, or at least breeze through it. Most candidates don’t know much in this section.
Are you familiar with SOLID design principles?
Do any of the following sound familiar to you:
- Single Responsibility Principle (SRP)
- Open Closed Principle (OCP)
- Liskov Substitution Principle (LSP)
- Interface Segregation Principle (ISP)
- Dependency Inversion Principle (DIP)
Have you heard of the saying “Prefer composition over inheritance?”
Can you explain that recommendation?
These questions are geared more towards actual development practices.
What’s the purpose of refactoring code?
Some points I’m looking for here:
- Remove duplication (DRY)
- Improve readability / ease of comprehension
- Enhance testability
- Isolate bugs or problem areas
- Improve performance
- Prepare for the addition of new functionality
What are some of the risks of refactoring? How can they be mitigated?
Refactoring means changing the structure of code without changing the behavior. The risk is that in the process of changing the structure, you inadvertently change the behavior. Mitigation strategies that I am hoping to hear include:
- Testing (unit tests)
- Utilize refactoring tools
- Refactor code in small steps
- Know the common refactorings and how and when to use them
Can you describe the differences between unit tests, component tests, and feature tests?
This one is somewhat controversial in the development community. Is the candidate aware of the different camps in the debate? Can they describe the various points of view? It opens up the possibility of follow-on questions:
- What is the purpose for each type of test?
- Have you ever used any of these testing techniques?
- What are some methods of implementing each type of test?
If I am familiar with the candidate’s language of choice (and I almost always am) then I like to ask them some specific questions about that language. I have a standard list of questions that I pick from. I don’t usually ask all the questions under a given language, but I like to have several prepared.
- What’s the difference between the
Integerobject and the
- What is an anonymous class?
- What is a nested class? Why would you use nested instead of anonymous?
- What’s the difference between checked and unchecked exceptions?
- What are generics?
- What are annotations? What are some things they can be used for?
- What is a virtual method?
- What is the C++ equivalent of an interface in other languages?
- What is a pure virtual class?
- What is multiple inheritance? What is the danger of using multiple inheritance?
- Are you familiar with the boost libraries? How about the new C++11 standard (previously called Technical Report 1)?
- What is the difference between a pointer and a reference?
- What are templates?
- Can you explain the concept of a delegate?
- What is a partial class?
- Are you familiar with LINQ expressions?
- What are generics?
- What is a nullable primitive type? How is it represented in code?
- What is a property? How is it different from a member variable?