Java programmer certification and interview questions

A cup of Java, from Flickr Earlier: Java programmer certification CX-310-065 preparation | James … I posted about preparation, I passed but didn’t get a great mark. The Sun exam objectives and overviews provide a lot of good information about what will be in the exam and I should have spent more time revising that material - especially since many of the concepts in Java 5 and 6 are still unfamiliar to me.

That’s ok, I passed and am currently working on the developer project. Much more comfortable for me.

If you arrive on my blog looking for interview questions and answers, I don’t do much of that. There are around 50 questions on this page. But a lot of those questions are about language stuff, for example:

38. Explain the Polymorphism principle.

41. What is OOPS?

22. What’s the difference between J2SDK 1.5 and J2SDK 5.0?

31. If you’re overriding the method equals() of an object, which other method you might also consider?

I wouldn’t be very excited about a job where the “technical experts” asked me any of these questions… #31 was brought up in the office as a *good* interview question. I disagree, 90% of the time you don’t need to override hashCode… it is a good idea to override it if you are going to stick it into a hashtable as the key, otherwise why care?

In one interview I was given a multi-choice assignment including a mix of Java API, syntax, JVM runtime configuration questions, then I was asked to write some basic code, using collections etc. In my experience, you are unlikely to see that; I thought it was a good idea, but I was fresh from Uni and understanding source code off the top of my head seemed important… now I don’t think it is.

These days, frameworks are available to write most of the application for you, the IDE is there to correct your syntax. Testing, code compliance and bug finding tools and plugins are available to check the logic of your code and fish out all the rubbish that bad habits encourage us to put in. Source control systems are used to allow peer review before your code becomes part of the main stream of work.

So why would an interviewer ask you questions about OOP and polymorphism? Or overriding equals - your IDE should warn you, but Eclipse doesn’t seem to, I checked.

You should be asked about previous experience, frameworks you are familiar with, technologies you understand… perhaps explain what is going on in a couple of tricky application code straight from the project they’d like you to work on. What blogs do you read… how do you approach a particularly difficult problem - is the answer Google it, see if anyone else has done the same thing… is there a framework to do it? what is it licensed under? My favourite is explain why Tomcat is or is not a Java application server. My least favourite is which frameworks have I worked with… everything is a framework, this could take a while.

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