Review: Devoxx 2013

As promised, here is my write-up for Devoxx 2013, the best Java conference in the world (maybe on par with JavaOne).

Day 0

Having work to do I arrived tuesday evening, day zero.

Devoxx wristband

For the second year in a row there was no line at all picking up the awesome wristband with NFC chip. This already is much better than most conferences which have lanyards with huge badges (yes, I’m looking at you JFall!). The Devoxx NFC chip is used by sponsors to get your email address and it is also used to check off lunch and the party to the Noxx. There is also a big sign in front of every conference room, there you can either give “Thumbs up” or “Thumbs down” after you’ve been to a session, with the NFC wristband. If there is no speaker presenting the huge movie theater screens show a tweet-stream, upcoming talks and the ‘best’ voted talks of the conference. A new feature this year was the middle ‘star’ in front of each conference room. If the queue of people gets too large you could ‘star’ a talk. When it becomes available online at Parleys it will automatically be suggested to you online!

Speakers dinner

The speakers dinner was, like every year, very well organized. And it gave me the opportunity to speak to the brightest minds in the Java community. It was really inspirational and eventually led to change my online identity.

Day 1

The first day of the conference. Up too early to film some stock footage before all the people arrive. One advantage was the empty tram from Antwerp city center to Kinopolis.


The start of the opening keynote had two guys (calling themselfs Meta-eX) where making amazing live music… with code! They used live-emacs to program Clojure code, which in turn used Overtone to play music in SuperCollider. Using not one but two Monome sequencers they made sequencing visible, displaying Clojure code with a beamer in the background.

After that Stephan Janssen gave us the latest Devoxx statistics, again maxed out with 3500 attendees (Devoxxians). He also talked about Devoxx4Kids with Daniel De Luca and they got a little present from Aldebaran Robotics: a Nao robot! He also talked about a substantial donation from Oracle for future Devoxx4Kids events!

The final part of the keynote was a demonstration by Oracle, they made a cool chess playing robot using multiple Raspberry Pi’s. After talking about the upcoming internet of things they looked at the history of the Java language and some bold design decisions under the hood, comparing the language to a wolf in sheep’s clothing. When the language Java was created it was pretty standard, looked a lot like C, but for blue collar programmers. But the technology under the hood was state of the art, not yet proven concepts. Today we take garbage collection, virtual machines for granted. When Java was created it was new and didn’t perform yet. The gamble payed off though, garbage collectors, JIT compilers and smart virtual machines caught up and now often outperform static C++ programs.

The Habit of Highly Effective Technical Teams

The next talk I could attend (had to do some networking and filming) was by Martijn Verburg. Lately he hasn’t been able to do a lot of programming but he’s working hard on his lean startup company and focuses on teamwork. In this talk he compared great agile teams with the Teenage Mutant Hero Turtles and other fun stuff. While actually making great points, for example: Having a shared goal. Like the TMHT, whom all fight for justice, your team has to have a shared goal as well. His talks are always full of humor but also have obvious and not so obvious rules, you’ll learn and laugh! This is exactly the reason our company (JPoint) flew him over for a day of hacking and a free talk for JUG members.

Teaching computer science with music

After being amazed by the Meta-eX performance during the keynote I decided to attend this talk by the programming member of the two man collective, Sam Aaron. He talked about his project Sonic Pi, a simple way to teach kids how to program. The main advantage of using music is the instant feedback during live coding. It was a nice inspirational talk about teaching and live coding music, and Sam Aaron is a great public speaker with huge enthusiasm.

Is it a car? Is it a computer? No, It’s a Raspberry Pi JavaFX Informatics System

Simon Ritter talked about using embedded Java with a Raspberry Pi to communicate with his Audi S3 to create a in-car information system, complete with touchscreen and accelerometer. After accessing the car’s CAN system he repurposed the steering wheel buttons for hands free control! A tantalizing talk about some real hardware hacking.

Hacking your own band with Clojure and Overtone

The final talk of the day was again with Sam Aaron, this time with his other band member Jonathan Graham. This time they explained how they created Overtone and other tools needed for their live performance like emacs-live. During the talk they often played some music making it a fun interactive experience. People asked questions and it was the perfect end of day one. The only drawback was Sam’s endless enthusiasm, every time Jonathan started a sentence he was interrupted by Sam… poor Jonathan. :-)

Beer Central

For the second time our company sponsored free beer at the famous ‘Beer Central’. The whole evening everybody was free to order any of the 300+ beers on stock! It was great fun and I caught up with a lot of (ex-) colleagues. The only drawback was getting back in the hotel around 06:10 after a wild night.

Day 2

For no obvious reason I decided to skip the keynote this morning.

Programmers are way cooler than musicians

Another talk about music, this time it was Geert Bevin talking about and playing on his eigenharp. It was a fun talk but I didn’t like it as much as most other people, it turned out to be one of the highest voted talks of the conference. Maybe it was the sound (which sometimes reminded me of the theremin, which I hate), or the fact I’d already been to two talks about music.

Java EE 7’s Java API for Websocket

Ah, a serious talk about Java EE by Arun Gupta. This for me was a bit of a disappointment. The talk itself was good, gave a lot of insight into the new features that you get from Websockets. But I got soon distracted. It reminded me about the small fight I had in 2009 about the new Servlet specification. The new websocket API again uses a LOT of annotations and yes, I understand there are some advantages for using them, there are also disadvantages. All the examples Arun showed used the annotations (and not the interfaces which are also there, yay!). For example:

@ServerEndpoint("/location")  //This is a good annotation, with meta information
public class SomeEndpoint {

   @OnOpen //Awww no this is where is goes wrong... it already says onOpen below
   public void onOpen(Session session) {

   @OnClose //No no no...
   public void onClose(Session session) {

   @OnError //NO!
   public void error(Session session, Throwable t) {

   @OnMessage //...
   public void textMessage(Session session, String msg) {
      System.out.println("Text message: " + msg);

The reasons I don’t like those annotations, and rather was to see adapters:

  • Interfaces are easier for code completion, ctrl-space knows what can be done
  • Testing is easier with interfaces
  • Less error-prone for beginning programmers (what happens on two OnOpen’s? Which annotations can I use? What can the method fingerprints look like?)
  • Annotations are for meta-data (like mapping!), not for describing code flow

During the sessions I tweeted about this and at the end of the sessions Arun opened the twitterfeed to check for comments. The only thing he said about my comment was “Roy, there is an Oracle document which describes when to use and not to use annotations, it is very clear, I’ll send it!”.

And here are those rules:

  1. When defining an API that an application is going to implement and the container is going to call, use an interface, unless one of the following rules applies.
  2. If an application class is providing an API that’s exposed to other applications, and that class also needs to provide methods that the container will call for lifecycle functions (or other container support or management functions), use an annotation to mark those methods so that the application has flexibility in the choice of names for those methods.
  3. If an application is going to expose an interface that another application (or user) is going to use without Java, use annotations to mark the methods that correspond to this interface. This avoids the need to define a Java interface that’s never going to be used by anyone other than the one class implementing the interface.
  4. If there can be more than one occurrence of a method for a given purpose, use an annotation.
  5. If an interface is chosen and the interface has many methods, consider providing an “adapter” class that implements all the methods with nop implementations. Applications can then subclass this adapter class to avoid the need to implement all methods. It’s often better to decompose the interface into multiple smaller interfaces.

(source: Annotation Rules)

As far as I can judge the first rule applies and non of the following rules break that.

Architecting Android Applications with Dagger

This talk surprised me! To be honest, the only reason I went to this talk was to have the best seat in the house for the JavaPosse… But I learned about a great framework. There is a problem using dependency injection frameworks in Android. The introspection and reflection is very slow and often causes the startup time to be 30% higher than it should be. This is why some of the great minds behind Google Guice invented Dagger. It originates from DAG-er which stands for Directional Acyclic Graph. It uses a separate compiler to analyze your code and generate new optimized injection code. This has two main advantages, if there is a problem in the graph it’ll show during compile-time not runtime. And second the processing is done at compile-time, so the execution is as fast has handwritten code!

JavaPosse LIVE

Another year at Devoxx, another JavaPosse LIVE. This year only two of the new posse were at Devoxx: Dick Wall and Chet Haase. But they teamed up with Emmanuel Bernard and Guillaume Laforge from the french programming podcast ‘Les Cast Codeurs’. It was the very first sessions at a conference I’ve seen where I left a little dumber, but I had a great time doing it.

Devoxx4Kids: Best Practises

Absolutely the best talk of the conference! Nah, just saying that because I was in it :-). During this talk Daniel De Luca, together with other Devoxx4Kids organizer (myself included) showed tools and best practises everybody can apply to get children into programming (your own kids, or a Devoxx4Kids session).

It was great fun, and only if one person in the audience decides to organize a Devoxx4Kids session, it was an absolute success.

BOF: Lessons learned from Devoxx4Kids

Instead of answering questions after the session we all went into a BoF room for an informal meeting. We had a lot of people talking about there experiences with children, from Arun Gupta teaching programming Minecraft to 200 kids to parents talking about their own experiences. Inspiring!

Devoxx movie: The Counselor

It wasn’t the best movie I’ve seen, it wasn’t the worst. It had the most crazy sex scene I’ve ever seen in a movie (catfish?), but also absolutely no interesting story line. It was very ‘american’ pointing out the obvious things instead of leaving anything to the imagination, which I didn’t like at all. Also, be prepared to leave the theater with a depression, no happy end. With this depression I didn’t go to the Noxx afterparty (where Meta-eX did an amazing gig!) but me and some colleagues decided to walk 4 km to the hotel, to reflect on life.

Day 3

Sorry for the incredibly long blogpost, I’ll keep the end short! The final (half) day at the conference I spend talking to a lot of people instead of going to the talks. I wanted to go to ‘Taming Drones: How Java Controls the Uprising of the Drone Force’ but it was full…

Introduction to Google Glass

The only talk I did attend was by Alian Regnier, one of the few GlassExplorers in Europe, he gave us his insight and shared his experiences with Google Glass after owning it for 6 months. It will no doubtfully infect us in a couple of years. He skipped over most of the code and instead talked more about his experiences as a Google Glass wearer. It was interesting to hear, but not that informative.


This Devoxx for me had a lot of: Music, Embedded devices (Raspberry Pi) and some Java EE. The organization was perfect as always (although I’d rather see a sandwich instead of the horrible salad). I still love the rock-and-roll bracelet with NFC chip. There wasn’t any big news, which was a bit of a shame. After announcing Devoxx FR two years ago, and Devoxx UK and Devoxx4Kids last year… it felt like 2013 was lacking something… I just don’t know what.

Also check out this amazing analysis of the conference tweets: