Abstract Java class loading plays a key role in the Java Remote Method Invo- cation (Java RMI) and Jini architectures by enabling code mobility overthe network. However, it has also saddled these architectures with a setof type compatibility and code downloading issues that commonly resultin run-time errors and programmer confusion. This paper describes theJava RMI class loading model and examines its ramifications.

Class loading is a powerful and distinguishing feature of the Java platform. Itenables Java processes to load application and system code at run time froma variety of sources, such as the local file system, a remote web server, or anin-memory buffer. It supports many diverse uses: remotely published Java ap-plets, pluggable application containers, code instrumentation, on the fly softwareupgrades, and run-time code generation, among others. Two interrelated architectures that heavily utilize class loading are Java Remote Method Invocation (Java RMI) and Jini network technology. Java RMI provides the ability to invoke methods on objects hosted within remoteJava processes. Jini extends the Java RMI programming model to support amore full-fledged notion of distributed services, incorporating both client- andserver-side computation, that can be discovered and used in an ad-hoc mannerover the network. Both Java RMI and Jini fundamentally rely on passing Javaobjects between Java processes, where the executable code for a transmittedobject may not be preinstalled in its destination. Supporting this form of objecttransfer requires dynamically loading the class definition for the object into thereceiving process. Without this functionality, supplied by Java class loading,neither Java RMI nor Jini would be possible.