javademos/sealed

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.

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.