Pretty much any language can do that in principle. Just run a compiler and build a DLL which you then dynamically load.

But this is clearly not what Alan Kay had in mind. He has clearly stated in the past that Java is not what he had in mind regarding object-oriented programming. If you have used Smalltalk, you would know Java is nothing like it.

Try modifying a Java class at runtime without shutting down the system. That is not going to work. Static typing is not late-binding. If you change the signature of a method at runtime and try to call it afterwards, then you would likely crash the whole program.

Static typing is not message based and cannot deal with dynamic change. It can only do so in a limited fashion through dynamic loading and reflection. But that is not the same as live modification of parts of your program already running.

Systems like Smalltalk could deal with that. Just like the internet can deal with a server going down without causing the whole internet to collapse.