Cay Horstmann

Just finished my workshop on Java in the Small at #baselone. Slides here: https://horstmann.com/pr...

On Wednesday 10:20 am I will present "Observing Project Valhalla" at BED-CON in Berlin. The organizers assembled a really interesting program this year: https://bed-con.org/2026... Hope to see some of you there!

On Wednesday 10:20 am I will present "Observing Project Valhalla" at BED-CON in Berlin. The organizers assembled a really interesting program this year: https://bed-con.org/2026... Hope to see some of you there!

On Wednesday October 14 I will present a workshop on using Java for small programming tasks at Basel One (https://baselone.org/#p.... I invite you bring your own tasks, or learn from some of mine. Hope to see some of you there!

Are you using Anki flashcards? Do you ❤️ its open source awesomeness? If so, consider donating through the app right now. Google is apparently making them remove the donation link in the next update. https://github.com/ankid...

One of my posts in this sequence did not succeed on BlueSky: Invalid app.bsky.feed.post record: grapheme too big (maximum 300, got 443). Raisin shitting is not limited to Germany...

Why not allow special characters and longish file names in a contact form? Making it difficult to do something easy is a German specialty. We call it the Korinthenkacker (raisin shitters). And apparently the IT outsourcing providers support it as a service when bidding on German jobs.

After a day of interacting with German web sites, I am reminded of Hanlon's razor (https://en.wikipedia.or...: "Never attribute to malice that which is adequately explained by stupidity." Or it's corollary, Grey's law: "Any sufficiently advanced incompetence is indistinguishable from malice."

Want to see what Native Image does with your code?🤔 Paste a snippet into this browser-based playground, compile it into a native executable, and inspect the generated machine code in ~10–15 seconds! 🚀 Try yourself: godbolt.elide.dev

I just got back from the JavaZone conference in Oslo. It was a lot of fun--highly recommended. All videos: https://vimeo.com/javazone My video: https://vimeo.com/122338... My slides: https://horstmann.com/pr...

Interesting issue about Java Valhalla performance: https://mail.openjdk.org... details at this nice blog: https://johan-sjolen.git...

At Basel One, I will present a workshop on Java for small coding tasks on October 14 and a deep dive into Java streams internals on October 15. This is one of my favorite conferences for networking. Hope to see you there! More at https://baselone.org

My trip report from JCrete: https://horstmann.com/un...

Valhalla has arrived in mainline Java (build 28-ea+10-569): jdk.java.net/28/ but my first sample program breaks the BlueSky 300 grapheme limit. Look here instead: foojay.social/@cayhorstman...

Who would have thought—a documentary about Java. Pretty cool. Watch it at https://www.youtube.com/...

PSA about white space in modern Java. Character::isWhitespace and String::strip are aligned. But the regex "(?U)\\s" differs in code points 28, 29, 30, 31, (Information separator 4...1) , 133 (Next line), 160 (No-break space ⚠), 8199 (Figure space), 8239 (Narrow no-break space).

At JCON, a speaker's slides had a mysterious reference to "danger to the herd". My preferred search engine (Kagi) led me to https://www.reddit.com/r... I had a good laugh at the "cliché developer with a conference t-shirt". Guilty as charged.

I just finished my talk at JCON—When Greed is Good: Understanding Java Stream Performance. The title attracted a good crowd. Slides at https://horstmann.com/pr...

I never thought much about hash codes of Java enumeration constants, but https://4comprehension.c... set me straight. Turns out enum hash codes are not stable, so serializing them as map keys will not work. Remedy: EnumMap!

I've been paying #Kagi for search since it's worth my time to get results instead of ads and slop. Added benefit: their translate service is fantastic for language learners. Where Google Translate gives the minimum, Kagi goes all out.

Is there any AI software that can watch a boring compliance video (emergency procedures, nondiscrimination, hazard communication, etc.) and answer the multiple choice questions that check for comprehension? Asking for a friend...

My article "Effective Pattern Matching 2026 Edition" is now live at https://javapro.io/2026/...

Github gives you until April 24 to opt out of using your Copilot interactions for model training. The setting is at the bottom of https://github.com/setti... Allow GitHub to use my data for AI model training.

Check out this fun project—Java in your browser in the most inefficient way imaginable, by having Wasm emulate x86_64 instructions running Linux running Java: https://bmarti44.substac... Jeff Martin and myself will explore better use cases for Java/Wasm at JavaOne.

Apparently bsky hates post > 300 graphemes. Mastodon doesn't: foojay.social/@cayhorstman...

Cool visualization of JDK releases and the JEPs from which they are made: https://juniverse.szanto...

Out with the old, in with the new... Bruno Borges created this site on modern Java usage: https://javaevolved.gith...

Cool article by Grzegorz Piwowarek about writing a gatherer, and then optimizing it: https://4comprehension.c...

Trying to understand how I got into the Sessionize list of 1124 most active speakers sessionize.com/most-active-... I had 8 talks accepted, at 5 conferences, and many more rejected—apparently enough for the top 3% of 39,000 speakers. A shout-out to all of them for submitting and presenting!

Jeff Martin and myself will speak at Java One (March 17-19, Redwood Shores, CA, USA) on Java and WebAssembly. Here is a $50 discount code if you register by Feb. 9: J12026SSM https://horstmann.com/pr... Speaker_Cay H.png

On Tuesday, February 10, Maurice Naftalin and myself will speak at Voxxed Days CERN on "Streams—Below the Surface". https://horstmann.com/pr...

On the plane to Stockholm where I will give two presentations at JFokus (https://jfokus.se/speak..., on Project Valhalla and the Java Class File API.

This Thursday I will speak at the Dublin JUG and the JChampionsConf, on Java pattern matching + a bonus talk for in-person attendees. In-person signup: ti.to/dublin-java-.... Start time 18:15 UTC To follow online, sign up here: www.eventbrite.com/e/jchampions.... Start time 20:00 UTC

The excellent free JChampions Conference 2026 (https://jchampionsconf.co) is happening online Thur 1/22/2026, Fri 1/23/2026, Mon 1/26/2026, and Tues 1/27/2026. Get free tickets from Eventbrite: https://www.eventbrite.c...

Here is my "Java Advent" article on nice and naughty cases of pattern matching, with nicer formatting than WordPress can muster, and the ability to leave comments without logging into WordPress: https://horstmann.com/un...

I participate in Advent of Code (https://adventofcode.co) to learn, and today I learned plenty. My naïve brute force solution for Day 8 required 3 minutes. I re-learned the union-find algorithm (never touched it since grad school, 45 years ago), and am down to < 1 sec. https://github.com/cayho...

My article "Nice and Naughty Cases of Pattern Matching" has been published in the JVM Advent Calendar: https://www.javaadvent.c...

This year’s JVM Programming Advent Calendar is open for business at https://www.javaadvent.c... Every day, a new post awaits. I enjoy this eclectic overview of what is new in the Java ecosystem.

There is always more to learn about Unicode. Today I found out about the aptly named WTF encodings: https://wtf-8.codeberg.page Java strings are actually WTF-16, not UTF-16. For example, the Java string "WTF\uD800" is not valid UTF-16.

Help--my LocalDate isn’t flattened! Just before my Valhalla talk at JFall, I found out that the early access build can flatten LocalDate arrays, but the latest version from Github cannot. Why? Serialization, of course. Read the gory details at https://horstmann.com/un...

On Thursday November 13, I will speak in Berlin on "Virtual Threads—A Second Look". https://www.meetup.com/j...

As I am updating my slides, another shoutout to https://imagetodrawio.com I upload a hand-drawn diagram and get something that I can clean up in draw.io Final result: https://horstmann.com/pr... That is how AI should be. Human in the loop. Tweakable result without endless prompting.

I'll be speaking at JFall on project Valhalla on November 6. https://jfall.nl

Core Java 14th edition, updated for Java 25, is now available in print or ebook at https://www.informit.com... and https://www.informit.com...

The latest Maven exec plugin can execute "instance main methods": https://horstmann.com/un...

I will give two talks at BED-Con 2025 (https://bed-con.org/202) on October 7 and 8 in Berlin.

After more than a year of trying off and on, I finally managed to fix my Emacs/LSP/Java setup. Now I can happily edit my Java scripts in Emacs instead of VS Code. Details at https://horstmann.com/un...

My take on Java 25: https://horstmann.com/un...

Following a suggestion from Stuart Marks (https://stuartmarks.wor..., I add JavaDoc as a search engine to my browser. I just updated the search URL to https://docs.oracle.com/...

$ java -version openjdk version "25" 2025-09-16 LTS Remarkably, the four numbers are perfect squares: 5², 45², 3², and 4².