Also I would say the answer is better left independent of the runtime environment. Yes you can load Java classes into the JVM. But why not have a serialization

Also I would say the answer is better left independent of the runtime environment. Yes you can load Java classes into the JVM. But why not have a serialization format that is independent of the vagaries and specifities of the JVM? Still, even if you lean on the JVM, that changes nothing about this particular problem. You don't need command pattern. You don't need a type hierarchy.