JDK 17 delivered JEP 409: Sealed Classes : https://openjdk.java.net/jeps/409
As well as being used for future classes this can be retrofitted to
suitable existing API classes where provably there can be no application
sub-classes since there are no public or protected constructors and
at least one package access constructor

A scan for these has identified various classes in the desktop module as candidates
Some of these turn out to have no subclasses and these should be marked final instead of sealed.

javax.sound.midi.Track has been identified as a class that could be made final