Runtime Support for Type-Safe Dynamic Java Classes

Modern software must evolve in response to changing conditions. In the most widely used programming environments, code is static and cannot change at runtime. This poses problems for applications, that have limited down-time. More support is needed for dynamic evolution. In this paper we present an approach for supporting dynamic evolution of Java programs. In this approach, Java programs can evolve by changing their components, namely classes, during their execution. Changes in a class lead to changes in the its instances, thereby allowing evolution of both code and state. The approach promotes compatibility with existing Java applications, and maintains the security and type safety controls imposed by Java’s dynamic linking mechanism. Experimental analyses of our implementation indicate that the implementation imposes a moderate performance penalty relative to the unmodified virtual machine. This work is supported by the Defense Advanced Research Project Agency (DARPA) and Rome Laboratory, Air Force Materiel Command, USAF, under agreement number F30602-97-1-0221. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright annotation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Defense Advanced Research Project Agency (DARPA), Rome Laboratory, or the U.S. Government.