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Jan Ouwens

@jqno.nl

142 followers 66 following 261 posts

Developer ◦ Java/JVM ◦ EqualsVerifier ◦ speaker ◦ @yoink.nl but opinions mine ◦ 👨‍👩‍👧 ◦ 🇳🇱🇪🇺 ◦ 🖖🏻 ◦ 💚 ◦ 🇺🇦🌻 ◦ he/him

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Jan Ouwens @jqno.nl · 17/09/2026

My ignite session is accepted for #JFall this year! > Designing a Lego model, or how my relaxing hobby turned out to be a software project in disguise This is the story of a two-week project that took me nearly two years to complete. Somehow I will make everything fit in five minutes.

Me with my Tilburg Lego Skyline model

Jan Ouwens @jqno.nl · 27/08/2026

Releasing a blog post and an EqualsVerifier in a single morning...things shoulldn't get any crazier today. Time to get some real work done 😅

Jan Ouwens @jqno.nl · 27/08/2026

EqualsVerifier 4.5.2 is out! It fixes an issue when you have a sealed hierarchy with a singleton enum that comes first alphabetically... Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 27/08/2026

I finally managed to get a Chromecast working in a vacation home! jqno.nl/post/2026/08...

Getting a Chromecast to work in a vacation home

In which I finally unlock an achievement that I’d been trying for for years

000

Jan Ouwens @jqno.nl · 21/08/2026

EqualsVerifier 4.5.1 is out! It now has a built-in prefab value for LinkedHashSet. As always, check the release notes at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 29/07/2026

Dear supermarket, why must you torture me so?

A box of eggs, fresh from the supermarket: 5 brown, 1 white

Jan Ouwens @jqno.nl · 13/07/2026

That's Thursday! Don't forget to sign up 😉

Jan Ouwens @jqno.nl · 07/07/2026

Want to see the insane talk I wrote about the insane programming language that I built? Join us at the @openvalue.eu meetup next week! www.meetup.com/openvalue/ev...

Building a Bullshit Language && Taming Null with JSpecify, Thu, Jul 16, 2026, 5:30 PM | Meetup

We're excited to announce our next meetup July 16th, 2026! As usual, we'll take care of food, drinks and awesome sessions - you just need to bring you ;-) This meetup will

Jan Ouwens @jqno.nl · 26/06/2026

I went to see Beat the other day: King Crimson veterans playing their 80s songs. At the end of the show it was hard not to agree with Adrian Belew:

Jan Ouwens @jqno.nl · 19/05/2026

I deleted my Twitter, closed my Dropbox account and installed a new OS on my phone: I'm trying to move away from Big Tech jqno.nl/post/2026/05...

Distancing myself from Big Tech

In which I replace services I’ve been using for literal decades

Jan Ouwens @jqno.nl · 17/04/2026

EqualsVerifier 4.5 is out! It adds a new check: it fails if you use java.net.URL's equals() method, because this will make a network call that can be flaky. (Convert to java.net.URI instead.) You can suppress this with a new Warning though. Check it out: github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 07/04/2026

EqualsVerifier 4.4.2 is out! It's a bugfix release that improves the layout of error messages, fixes a small bug with Kotlin lazy fields, and fixes two other minor issues. Check it out: github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 23/02/2026

EqualsVerifier 4.4.1 is out. It contains a bug fix for floats and doubles. See also: github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 21/02/2026

EqualsVerifier 4.4 is out! It contains a fix for Java 26's "final means final" warnings. (Yes, I know Java 26 not released yet 😅) Check out the changelog at github.com/jqno/equalsv... and also the updated manual at jqno.nl/equalsverifi... #java

Reposted by Jan Ouwens

Rune Flobakk @rune.flobakk.org · 18/02/2026

Agreeing with everything! And I also cross my fingers for the teased piece on (or yelling at) JPA, because it sounds like even more I would keep agreeing to 😁

Jan Ouwens @jqno.nl · 17/02/2026

My story on database schemas is published in the (Dutch) Java Magazine! Unfortunately it had to be shortened, so if you want to read the full version (or don't have access to Java Magazine), you can find it on my blog! jqno.nl/post/2026/02...

My story in the printed edition of the Java Magazine

Jan Ouwens @jqno.nl · 24/01/2026

EqualsVerifier 4.3.1 is out! It respects the Kotlin data class contract as described here: kotlinlang.org/docs/data-cl... As always, check out the changelog: github.com/jqno/equalsv... #java

Data classes | Kotlin

Jan Ouwens @jqno.nl · 15/01/2026

I just found out that my Lego model of the Tilburg city skyline was put up for sale on AliExpress without my knowledge or consent. I guess that means I'm in the big leagues now!! 😂 (It's cheaper if you go through bricklink.com BTW 😉)

Advertisement for my Lego Tilburg Skyline model, on AliExpress. It could be yours for € 53,69!

Jan Ouwens @jqno.nl · 05/01/2026

My J-Fall (@nljug.bsky.social) talk is now on YouTube! www.youtube.com/watch?v=4nVc...

Less is more: reduce $ and CO₂ to improve performance 🚀 and joy 🥳 I Jan Ouwens

YouTube video by NLJUG

Jan Ouwens @jqno.nl · 01/01/2026

EqualsVerifier 4.3 is out! It fixes an issue with consecutive calls to `ScanOption.except()`. Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 30/12/2025

EqualsVerifier 4.2.6 is out! 🎇 For sealed types, it can now use all permitted non-abstract subclasses instead of only the first one, which is handy if the first one has a recursion. It also fixes a potential bug for records. As usual, check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 03/12/2025

EqualsVerifier 4.2.5 is out. It runs slightly faster, and is slightly better factored! Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 02/12/2025

Frank interviewed several experts, and me, about sustainability in IT at J-Fall for the @foojay.io podcast. I like how it came out!

Jan Ouwens @jqno.nl · 27/11/2025

I spent 6 hours in MS Teams meetings today. Let's not repeat this any time soon...

Jan Ouwens @jqno.nl · 25/11/2025

EqualsVerifier 4.2.4 is out! Some people reported an UnnecessaryStubbingException caused by EqualsVerifier. This is now fixed! Check out the changelog at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 15/11/2025

EqualsVerifier 4.2.3 is out! It contains some small improvements for tests that are run on the module path. Also, it improves on error messages when Mockito is in use. Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 09/11/2025

EqualsVerifier 4.2.2 is out! It now supports EnumSets and EnumMaps for enums with only one value. Also, I fixed an error message that referred to Warning.ZERO_FIELDS, which was removed in version 4.0. All in all, very exciting stuff Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 06/11/2025

Thank you to everyone who joined my talk at #jfall today! You can find my slides here: jqno.nl/talks/slides...

Less is more: reduce $ and CO₂ to improve performance 🚀 and joy 🥳

Jan Ouwens @jqno.nl · 04/11/2025

I'll be at #JFall next Thursday! Hope to see you there!

Promo picture for my talk at J-Fall: "Less is more: reduce $ and CO₂ to improve performance 🚀 and joy 🥳", November 6th 2025, Pathé Ede

Jan Ouwens @jqno.nl · 29/10/2025

EqualsVerifier 4.2.1 is out! It fixes an issue with Kotlin lazy delegates with a generic type. Check out the changelog at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 27/10/2025

I really appreciate that license! I often try to game it in my PRs by having 0 surviving issues on the first try. I just opened a big PR and managed to kill 187, but 7 still survive. I'm a little bit proud of myself now. But I'm also happy that I get to ship without those 7 issues that I missed!

Jan Ouwens @jqno.nl · 18/10/2025

It turns out the YouTube app on my tv was set to Dutch, and I could change it in the settings. I set it to English which fixes my problem! (And probably introduces the new problem of translating all Dutch videos into English...but we'll cross that bridge when we get there) Thanks @bjeaurn.com !

Jan Ouwens @jqno.nl · 18/10/2025

My "smart" tv is translating YouTube video titles to Dutch and I hate it. The phrasing feels awkward. More importantly, it suggests the videos are in Dutch, which they're not.

My "Watch later", I mean "Later bekijken" playlist on YouTube with a bunch of Devoxx videos with Dutch titles

Jan Ouwens @jqno.nl · 03/10/2025

EqualsVerifier 4.2 is out! It has prefab values for Java 25's ScopedValues, but the main attraction is that support for #Kotlin delegates is greatly improved! They're now much easier to work with, and also error messages are much clearer. Check out the details at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 30/09/2025

I just upgraded EqualsVerifier and I have to say, the process was extremely painless! I had exactly 1 deprecation to deal with and that was it.

Jan Ouwens @jqno.nl · 22/09/2025

EqualsVerifier 4.1.1 is out! It fixes an issue with classes that extend Enum Check it out: github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 02/09/2025

EqualsVerifier 4.1 is out! It adds the method withResettablePrefabValues, which allows you to have values that are re-inintialized after each check that EqualsVerifier runs internally. Handy for values that mutate when they're used. See github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 27/08/2025

Looks like I'll have to update my blog soon: there's a new player in town 😄

Reposted by Jan Ouwens

Benjamin Marwell ☕ @bmarwell.de · 26/08/2025

So, here is my new #java side-project: jdtfmt - a Java #formatter for the command line. * Can be paired with #spotless (both use jdt). * fast (native) github.com/bmarwell/jdt... Thanks to @jqno.nl for the inspiration, @mthmulders.bsky.social for #graalvm hints and @bdemers.io for encouraging me 😀

GitHub - bmarwell/jdtfmt: jdtfmt is an opinionated java source code formatter for the command line

jdtfmt is an opinionated java source code formatter for the command line - bmarwell/jdtfmt

Jan Ouwens @jqno.nl · 22/08/2025

And EqualsVerifier 4.0.9 is out, too! Sometimes you introduce a bug while fixing one... 🤦🏻‍♂️ Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 22/08/2025

EqualsVerifier 4.0.8 is out! It fixes an issue with abstract sealed types that add state and need `Warning.NULL_FIELDS` suppressed. Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 20/08/2025

Yes let's hide the important stuff, thanks GitHub

Screenshot of a piece of GitHub diff saying "Load diff - Large diffs are not rendered by default."

Jan Ouwens @jqno.nl · 06/08/2025

Somehow, Microsoft Outlook has found a way to make GitHub notification mails even more annoying than they already were

Three GitHub notification mails, with the tag [SUSPECTED MARKETING] added to them for no reason

Jan Ouwens @jqno.nl · 30/07/2025

EqualsVerifier 4.0.7 is out! It fixes a bug with file path separators on Windows when using forPackage() See github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 18/07/2025

EqualsVerifier 4.0.6 is out! JPA entities with lazy fields must use their getters in equals. EqualsVerifier checks this but can't do it if the getter is final. It now throws an error if the getter is final instead of silently skipping the check. Check it out: github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 14/07/2025

I know Kotlin is the cool, hip thing these days, but the mysterious ways it generates bytecode for some of its syntactic sugar features makes my life as EqualsVerifier maintainer pretty difficult in ways that Scala never did

Jan Ouwens @jqno.nl · 07/07/2025

EqualsVerifier 4.0.5 is out! It fixes a regression when testing relaxed equals relations. Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 06/07/2025

I _love_ the idea of self-hosting things. But when you self-host, you're always on-call for the things you self-host. I _hate_ being on-call. So I'm at an impasse....

Jan Ouwens @jqno.nl · 03/07/2025

EqualsVerifier 4.0.4 is out! For those times when you need an array of an enum type that only has 1 element Check it out at github.com/jqno/equalsv... #java

Jan Ouwens @jqno.nl · 23/06/2025

EqualsVerifier 4.0.3 is out! forPackage can now also scan jar files, which is handy for certain kinds of integration tests that run against jar files instead of directories with .class files. Check it out at github.com/jqno/equalsv... #java