So for people (like me) who were surprised by how modern the Java code looked like… here are the following features/JEPs involved in the Java code:

Finalized features:

- JEP 395: Records, finalized in Java 16: https://openjdk.org/jeps/395

- JEP 409: Sealed Classes, finalized in Java 17: https://openjdk.org/jeps/409

- JEP 441: Pattern Matching for switch, finalized in Java 21: https://openjdk.org/jeps/441

Preview Language Features:

- JEP 430: String Templates, preview language feature since Java 21: https://openjdk.org/jeps/430

- JEP 445: Unnamed Classes and Instance Main Methods, preview language feature since Java 21: https://openjdk.org/jeps/445