A dynamic, portable and safe approach to byte-code transformation

A powerful feature of the Java programming language is its user-definable class loading policy, which when combined with the namespace independence between class loaders, allows portable implementation of semidynamic program transformations. Such transformations can be used for a range of purposes, including optimization and semantic extension. In this paper we present a framework for semantic extensions in Java. This framework consists of a number of simple but powerful transformations that, among other things, allow us to semantically extend Java to provide orthogonal persistence. The use of semi-dynamic program transformations lends our orthogonally persistent Java a number of important qualities, including simplicity, portability and a clean model of persistence. Significantly, our implementation is efficient, outperforming PJama, a well-known orthogonally persistent Java, which is based on a modified virtual machine. In addition to describing the application of these transformations to orthogonally persistent Java, we foreshadow their use in a number of other contexts, including implementing multiple inheritance for Java, and dynamic instance and class versioning.