On Wednesday, November 5th, 2025, NLJUG will be hosting expert-level pre-conference Masterclasses as part of J-Fall 2025

These 4-hour sessions will offer deep insights into the latest Java technologies and trends, providing a unique opportunity to learn from top industry experts. Details about the location and speakers will be announced soon, so make sure to stay tuned and follow our socials for the latest updates!

Don’t miss out on this fantastic opportunity to enhance your Java knowledge and connect with the community ahead of the main event!

Ticketing for the preconference will be open on October 1st. 

Workshop 1 – Rick Ossendrijver & Tim te Beek
Breaking your testing habits

Old habits are hard to break; did you know starting JUnit test methods with `test` was last needed in 2006? With JUnit 6 and AssertJ 4 around the corner it’s high time to (un)learn and phase out lingering test patterns. Join us as we take you through the patterns and libraries of decades past, and help you into the new in this interactive workshop.

With two experts in automation on hand, each with their own experience and tool suites, upgrading becomes a breeze. Say goodbye to Hamcrest, TestNG, JUnit 3/4/5, and adopt AssertJ and other best practices. Bring your projects and a will to change, and be ready to walk out with a fresh new test suite for the decade to come.

Workshop 2 – Urs Peter
Fast-Track to Kotlin for Java Developers

Are you a Java developer with no or minor experience with Kotlin, and do you want to master this promising language in a very short time? Then this workshop is for you!

In just one day, you’ll dive into Kotlin’s most powerful language features for production use and learn how to apply them in a clean, idiomatic way.

Through live coding, real-world anecdotes, and plenty of hands-on exercises, you will not only learn how Kotlin compares to Java but also experience firsthand how it can improve your productivity and code quality.

The following topics will be treated in-depth:
• Object Orientation – discover Kotlin’s concise and readable class and interface syntax
• Null Safety – and other safety features that make the dreaded NPE a thing of the past
• Collections – unleash their expressive, functional power
• Extensions – create fluent, discoverable glue code to bridge APIs and layers
• Control Structures – orchestrate business logic in a clear, expressive manner
• Java Interoperability – experience how Java libraries can get a tremendous boost in usability with Kotlin spice.

Along the way, you will learn how features like immutability, expression-oriented programming, and functional constructs and collections help you solve problems in an elegant and effective way.

Finally, you’ll bring everything together by building a Spring Boot application that combines all of the above features —giving you a working reference implementation that shows how to unlock the best of Kotlin in an idiomatic way.