About me

My name is Jan Ouwens and I’m a developer from the Netherlands. Currently, I work for Codestar. I do a bunch of things:


  • EqualsVerifier - [site] [github] [java]
    A tool to make rigourously testing Java’s equals and hashCode methods a one-liner
  • Parallel Java - [github] [java]
    A Todo Backend written in Java, without using annotations, to support my talk Java from a Parallel Universe
  • PicoTest - [github] [java]
    An ultra-minimal unit-testing framework, based on the JUnit 5 Platform
  • Foobal - [site] [github] [scala]
    A program I use to predict the outcome of soccer matches, so that I can participate in the family pool without needing to learn about the actual sport
  • ReminderMail - [site] [github] [kotlin]
    A small Android app that makes it easy to quickly send mails to yourself
  • ComposeKey - [site] [github] [scala]
    A bundle of text-expansion snippets for Alfred that mimic the behaviour of Linux’s compose key
  • vim-reversal - [github] [vimscript]
    A colorscheme for Vim that highlights identifiers and de-emphasizes keywords, so you can easily see what’s important in your code


  • Java from a Parallel Universe - [link]
    What Java would look like in a world where annotations were never invented.
    Delivered at J-Spring.
  • Don’t hack the platform? ☠️💣💥 - [link]
    A funny anthology of tricks and hacks for the JVM.
    Voted 2018’s “best non-Venkat talk” by the J-Fall audience!
    Delivered at J-Fall, JavaZone, JBCNConf and more.
  • Not all equals methods are created equal - [link]
    How to write a good equals method, and to test it with EqualsVerifier.
    Delivered at Devoxx.
  • Growing a DSL for financial calculations - [link]
    The story of how my colleague and I ‘discovered’ a Scala DSL for writing complex mortgage calculations.
    Delivered at Typelevel Summit Oslo and Codestar Launch Event.


  • 2011 - present, tr ouwens - [site] [english]
    my tech blog
  • My publications in the Dutch Java Magazine
    • October 2018, Lees dit niet! ☠️💣💥 - [site] [dutch]
    • February 2018, Selenium is leuk met ScalaTest - [site] [dutch]
    • April 2016, Een DSL kweken - [site] [dutch]
    • June 2015, Grip op je buildproces met Gradle (met Hanno Embregts) - [site] [dutch]
  • 2009 - 2012, Brief en leed - [site] [dutch]
    a funny letter-writing blog I did with my friend Ralf
  • January 2008, Voorstel voor een methode voor de kwantitatieve analyse en vergelijking van beeldverhalen - [PDF] [dutch]
    a way too in-depth survey of Asterix jokes
  • August 2005, The Performance of Wireless MPEG-2 Video Streaming - [PDF] [english]
    my Master’s Thesis