Binkley says that you can do hot (runtime) patching in Java now - from this article we get the following:

But ah-hah! We do, we can use a different implementation of FunctionTable which stores the method body as a String in Derby and uses BeanShell (or Janino!) to invoke it. So a method invocation is completely configurable at runtime! Not deploy time, runtime. If you find a bug, you can fix it without a redeploy.

Uh, yeah. Go read the whole post to see just how simple it really is. meanwhile, all I have to do in Smalltalk is load in a new version of my code, and I'm done.