Since JDK 9, Java, as a language, has evolved faster than at any point in its 30-year history. For developers, this is great as it means we get more new features to make our code more concise, yet hopefully, easier to read and understand.

All new language features also bring their quirks and possibly unseen consequences.

In this fun interactive session, we’ll examine a range of recent language features and pose questions to the audience about how the code works and what it does.

We’ll cover many of the new language features from recent releases, including switch expressions, sealed classes and pattern matching. We’ll even look at some curious behaviour in Jshell and how some special characters can be used in unexpected ways.

The answers will most definitely not always be as you expect.

Jfokus

A conference talk exploring tricky edge cases in modern Java features, structured as interactive puzzles. Topics covered include exhaustiveness rules for switch expressions vs switch statements vs enhanced switch statements, primitives in pattern matching (JDK 23+), pattern dominance with primitive and wrapper class mixing, guarded patterns and their compilation rules, and Unicode identifier quirks. Key takeaways: switch expressions must be exhaustive while classic switch statements need not be; enhanced switch statements (using new syntax) also enforce exhaustiveness; mixing primitives and wrapper classes in the same switch leads to confusing and sometimes broken behavior; constant case labels take priority over guarded patterns; and Unicode soft hyphens and end-of-file characters can produce surprising compiler behavior.

Modern Java Puzzlers, by Simon Ritter