Updating from Java 21 to 25 is a smooth experience. Unless you're working on an unlucky project that collected all the little details that change: Whether it's annotation processing, null checks, file operations or the removal of old technologies, Peter collects them all.

nipafx (Nicolai Parlog)

A guide covering the breaking changes and migration considerations when upgrading from Java 21 to Java 25. Topics include final record pattern variables, null checks in inner class constructors, file system operation changes on Windows, Unicode/CLDR updates and COMPAT removal, removal of 32-bit support and GTK2, deprecated and removed JVM command-line options, changes to Thread and ThreadGroup methods, separate Metaspace and GC printing, and remote debugging changes with jstat and jhsdb. The post is primarily a companion to a video, providing timestamped chapter links and reference JEPs and JDK bug tracker issues.

Upgrading From Java 21 To 25: All You Need To Know