"In the world of XML-based Web services and SOAP, you would process the document upon receipt, possibly solving the equation. Imagine, however, what happens when you receive such a document but do not know how to solve differential equations. Even if I place a special note on the document asking that you, please, solve the formula before displaying it, you can't do that without knowing how. In the mobile code world, I would not only send you the differential equation, but also the instructions needed to process it. You could load those instructions into your mental "virtual machine" and solve the formula. Thus, although you lack prior capabilities to process a piece of information that came from the network, the network provided you with the solution—the instruction codes—needed for that processing."
An interesting comparison on the activity and developer size of Jini vs JXTA and companies using Jini over J2EE:
"In effect, XML is the answer, not Java. At least it is the answer chosen by users. The short history of computer networking tells us that heterogeneity is best served by platform-neutral communication protocols (such as TCP/IP and HTTP). Jini does just the opposite. It embraces a diversity of protocols, allowing each service to have its own system of communication, so long as it can supply a Java proxy object that understands this system to a client. Rather than make the communication system the locus of commonality, Jini makes the computational system, Java, the locus. I will bet that the JXTA peer-to-peer project (www.jxta.org), which defines platform-neutral communication protocols, will eclipse Jini as a vehicle for distributed computing, simply on that account, as Web services already have."
An interview, with Rob Gingell who is Sun Microsystems' chief engineer, fails to say much at all except that maybe J2EE is the path of least resistance and that Jini is as successful as client side Java.