# sealed — Sealed classes and interfaces

Companion code for the ankurm.com article **Sealed Classes and Interfaces: Modelling Domains with Exhaustive switch**. The explanation lives in the
article; this folder holds the runnable sources and the transcripts they produced.

```bash
JDK25=/path/to/jdk-25 JDK27=/path/to/jdk-27 [JDK21=/path/to/jdk-21] ./run.sh    # regenerates output/*.txt
```

- `src/` compiles and runs unchanged on 21, 25 and 27: the `Payment` model, the three subclass modifiers, generic and recursive hierarchies, the `default` trap and a visitor for comparison.
- `broken/` fails to compile on purpose (one rule per file).
- `sep/` shows what the JVM itself enforces when a class file disagrees with the sealed type it claims to extend.
- `jackson/` runs the same `Payment` through Jackson 3.2.3 (`./jackson/fetch.sh` downloads and sha1-checks the three jars from Maven Central; they are not committed).
- `multi/` is a named module, the only place a sealed hierarchy may span packages.

Tested on Temurin 25.0.4.1+1 and 27+35, and OpenJDK 21.0.10 as the baseline.