Flexible Runtime Program Adaptations in Java -- A Comparison

Software development is an ongoing process which does not end when the first version of an application is released. Bugs must be fixed and requirements evolve. Maintaining an application usually means to stop the application, apply the required changes, and start the application again. This downtime is not acceptable for applications that must be available 24 hours a day, 7 days a week. On the other hand even for end-user desktop applications, restarts to apply patches can be an annoying user experience. For that reason we investigate how to maintain applications at runtime. However, due to the fact that it is not predictable what changes become necessary and when they have to be applied the application must be enabled for unanticipated changes even of already executed program parts. In previous work we proposed a solution for Java, since Java is commonly used for developing 24/7 applications. Unfortunately, this solution came with some limitations. Therefore, we present a novel runtime maintenance approach based on class replacements and mediators which overcomes these limitations and allows unanticipated changes of applications that run on top of a standard Java virtual machine.