None of these examples are especially illuminating here. In my opinion, two things really exhibit this "code over the network" nature; the class URLClassloader that's been in Java forever and the JVM SecurityManager system. URLClassLoader will load bytecode from any url; give it a url to a jar at some domain and it'll load it. The JVM security model was intended to let app developers define exactly what code could be executed, and what resources could be accessed on the client machine.

The other stuff like JNI (a registry for RPC endpoints) and java rmi itself were baked into the standard libraries from the beginning as well. But the envisioned "software agents running on arbitrary machines on the network" never took off, seems kind of foolhardy in hindsight, that anyone would think that's a good idea.

And somewhat less well known, probably, but cool and potentially useful, nonetheless: ObjectSpace Voyager. It was a framework for mobile code / agents / distributed computing. I tried it out a bit, liked it. ObjectSpace were also the company that came out with JGL - the Java Generics Library, a commercial library for generics in Java, some time before Java itself got generics or even before the Java Collections API came out. I think JGL was inspired by C++'s STL (Standard Template Library).