Summary

Historical data for past JDK releases are missing the list of permitted subclasses for sealed classes and interfaces, making those sealed types non-sealed.

Problem

The historical data for past JDK releases are not recording the permitted subclasses for types correctly. As a consequence, certain casts and subtyping hierarchies are allowed when using --release N for JDK >N, despite being illegal. Consider for example JDK 21 and JDK 22 javac:

public class C {
    public static void main(String... args) {
        Runnable r = null;
        System.err.println((Thread.Builder) r);
        System.err.println(r instanceof Thread.Builder);
    }

    private abstract class CCC implements Thread.Builder {}
}

$ JDK21/javac /tmp/C.java
/tmp/C.java:4: error: incompatible types: Runnable cannot be converted to Builder
        System.err.println((Thread.Builder) r);
                                            ^
/tmp/C.java:5: error: incompatible types: Runnable cannot be converted to Builder
        System.err.println(r instanceof Thread.Builder);
                           ^
/tmp/C.java:8: error: class is not allowed to extend sealed class: Builder (as it is not listed in its 'permits' clause)
    private abstract class CCC implements Thread.Builder {}
                     ^
3 errors

$ JDK22/javac --release 21 /tmp/C.java 
$ --no error--

Solution

The historical data will be fixed to include permitted subclasses.

Specification

No specification change. The historical record will be fixed for JDK release 17-21.