public final class StockTransaction extends Transaction { } How sealed classes work. The key concept with sealed classes is that they are declared using the sealed keyword, followed by the permits ...

When a class extends another, instanceof works, but not when a class implements an interface or abstract class, you cannot use it. It would be nice to have an operator of its own that allows this ...

Now Java.registerClass can only implement interface, but can not extend abstract class, just like below: const myOutputClass = Java.registerClass ... Java.registerClass should be able create new java ...