Wednesday, 31 March 2010

Scientific rumours from CERN

As you may be aware, the CERN large hadron collider performed it's first high energy collisions just the other day. The official statements are that it will take many months or even years to collect and analyse the data. However, early data already suggests some interesting findings.

Not one not one but two kinds of strangelet appear to have been created. The first turns other particles into strangelets as it contacts them. This might have caused a world-ending reaction had it not been for the second kind. Once a sufficient density of the first strangelets exists in an area, a kind of anti-strangelet appears. This exerts a strong attraction force on other particles, and causes the first strangelets to revert back to normal matter. The strong attraction force suggests this might be an unexpectedly different form of the long sought-after Higgs particle, though this is yet to be confirmed.

The scientists have informally dubbed the first strangelets as "wise particles" or "cluons" as they mimic the way knowledge is passed from person to person. The opposite strangelets' flocking behaviour and cancellation effect on wise particles has led to them being dubbed "fools".

So, today April 1st, scientists can claim to have identified Higg's Bozo.

Monday, 29 March 2010

Programmer interviews and coding tests

Jeff Atwood has another blog post up about how "the vast majority of programmers can't program at interview".

Having interviewed programmers, and having thought about this problem from a human factors perspective, I've usually come to the conclusion that coding tests at interview are, in the end, almost useless.

Let's describe this using a slightly different story...

Suppose I was interviewing someone -- let's call him Bert -- for a human factors job. I ask him:
"Bert, why do you think programming interview candidates usually fail simple coding tests, even when all the other empirical evidence (their career thus far, references, and degree from a top rated university) suggests they should be competent?"

And Bert responds:
"Because they're just all that dumb; top tier university professors are fools who can't assess students; the exam results are all fake; and programmers' bosses are all just bozos that can't see whether any code is being produced even if they are programmers themselves. The empirical evidence from the rest of their careers is wrong and my toy interview question asked by an untrained interviewer over the telephone is right!"

Bert would not be getting the job. (However much the grumpy misanthrope in me might want to cheer him on in railing against the world!)

Like it or not, coding at interview is very different from coding on a job. To use a loose analogy: a great many people struggle at public speaking -- shove a microphone in front of them and ask them to talk for a minute about rain, and they say "Um, er, um... Mummy can I go home now?". That does not mean they don't know English or what rain is. Dumbing the question down to "Ok, just talk about water then" doesn't solve the problem - because it wasn't the topic that was the problem in the first place.

In an interview, we have a fake task (nobody wants to use the code), in a fake setting (an interview), via a false interaction (over the telephone!), with a false assessment (one interviewer whose word is final, no compiler, no user, no sales, no code metrics or unit tests), a fake timeframe (a few minutes on each 'project'), false pressures (your job depends on the next ten lines of code), and somehow we expect to have valid results. Speaking as a scientist, that's just nuts.

At this point, most people reply "Sure, but we don't care about missing out on good candidates, only not hiring bad ones." I have worse news for you. You are probably still hiring as many bad candidates as if you selected your candidates by rolling dice. Most interview coding tasks are so over-simplified that they no longer select for programming or thinking skills at all -- the "programming on stage" skill dominates completely. The irony is that by selecting for "skill at interview coding tasks" you might find yourself effectively selecting for people who have done a lot of interviews and honed that skill -- but you actually want to hire the person who has hardly done any interviews because no company ever wants to let him leave.

Tuesday, 9 March 2010

JavaFX initialisation order (solved?)

The semantics of JavaFX's initialisation order can be hard to find, and in a previous post, I was finding it gave some odd effects. Having looked on the JavaFX bug tracker, it turns out it the issue is fairly simple, but needs trumpeting from the hills because it is still unexpected. will be null. How is that possible? Because of what override means -- it changes the definition but not the "order of declaration".

A naive person might think that would first be set to 1 (in the initialisation of A) and then to 2 (in the initialisation of B). Or they might think that B.two will be set before because it comes first in B's script. But that's not how JavaFX does it. The variable one is initialised first because it is declared first (in A's class declaration, which comes before B's.) But it is set to B.two because only the override initialiser takes place. Unfortunately, this means it is set to B.two before B.two has actually been defined -- so it gets set to null.

The moral of the story: Don't use override var if you want to set the variable to refer to another member variable. It's a forward reference. Even if the member variable you want to refernce also comes from a superclass, it could still be a forward reference (because you don't know what the order of declaration was in the superclass).

If in doubt, set it in the init block. That always happens in the order that you specify in the block, after everything else has happened. It's boring and more Java-like, but at least you can even step through it with a debugger and put log messages in if you need to!

Tuesday, 2 March 2010

JavaFX initialisation craziness

UPDATE: Another post describes the solution.

JavaFX is Sun/Oracle's new user interface platform for Java. It has many features that are quite nice. But it has a few oddments that are hair-pullingly irritating.

The naïve among us might think that pushing the mouse button would indeed be wired through to MyBehaviour.onMousePressed, and "MOUSE PRESSED" would be printed. Apparently not.

In the language reference, there is this irritating line when it describes the initialisation order:
The values of the object literal's instance variable initializers are computed (but not set).

"but not set". Of all the evil villainous schemes... The MySkin and MyBehaviour objects are created, but isn't actually assigned until later, so the following line wiring the mouse events to it breaks.

I keep finding that JavaFX is wonderfully concise, but really tricky to debug, and irritatingly fragile as many of its conventions don't do what you'd expect (like let you refer to an assignment you made in the previous line during initialisation, as in this example).