Tuesday, June 9, 2009


Yep, its another blog/article on interviewing. I just searched on google for "interview programming" and got 21.8M hits. So what's so bad about one more? :)

I wanted to have a few words about interviewing for mid-level and senior developers. I do this for my company as one of my many functions (including software architect and lead developer). The reason I feel compelled to write is disappointment. I just cannot reconcile how good some resumes look and how poor the results are off the paper.

When I interview, I *never* *ever* go the puzzle/trick route. I think those have very little to do with our jobs at best and give misleading results at worst. To me, you should focus where the big cost items are in software - in its (lack of) structure and in its (lack of) flexibility. Does the code smell?

It is how easily the software can be changed over time that determines its real cost.

So when I interview, I first establish that they have good grasp of object orient design fundamentals. Then I focus on the key area of "best practices." Does the candidate understand when they are creating a mess? Do they recognize conceptual pollution when they see it?

To ascertain this, I give them a take home (java) "test." I want them to not feel a great deal of time pressure (when was the last time your boss dropped a programming task in your lap and said it needed to be done in 20 minutes?). I give them overnight to complete the test, but in reality it should only take them 20 minutes.

The actual test is short. It's a two page code sample for them to critique. I tell them that their boss is interested in hiring the developer of that code and boss wants their feedback. The test shows the following kinds of problems:
  • embedding strings directly in code
  • mixing of abstractions
  • blocks of code commented out (with no other explanation as to why it was commented out)
  • the use of public virtual functions called in a constructor (a questionable practice)
  • complete lack of comments
  • errors in relationships (coder assumed 1:1 when its really 1:N)
  • missing abstractions (over use of string data)
  • over-reliance on open-ended integers (instead of enums)
In all, there are about a dozen issues that could be flagged. I have had several candidates tell me that everything looked good to them. My average score is probably 5 issues. I tend to get interested in a candidate if they score 7 or more. The best I have seen was from a really, really good developer who did it sight-unseen in about 10 minutes and got 14 issues (I give credit if they raise and can defend most technical concerns).

I don't consider this tricky questioning. It basically boils down to me having developers that don't keep me awake at night wondering what messes they are making. I feel that a competent developer ought to be able to get most of this almost by instinct.

So why do 90% of the candidates not make the bar?