Improve readability

Hi this is not the most important thing in the world, but triggered by this [tweet](https://twitter.com/gilesgoatboy/status/339944435729186816) I was intrigued by the code.

After understanding the code, I could not think of anything better than propose a fix. 

Using `!` always confuses me, so I simplified the if-clause, and
also made the intention of the code a bit more clear by adding
a single comment-line, which imho is ok here.

Note: I am not a java programmer, I have no environment setup so I was not able to run any tests, but I am pretty sure my code is identical to the previous version, and I hope it is more readable as well :)

Hope I got it right :)