SUMMARYSoftware is changed frequently during its life cycle. New requirements come, and bugs must be fixed. To update an application, it usually must be stopped, patched, and restarted. This causes time periods of unavailability, which is always a problem for highly available applications. Even for the development of complex applications, restarts to test new program parts can be time consuming and annoying. Thus, we aim at dynamic software updates to update programs at runtime. There is a large body of research on dynamic software updates, but so far, existing approaches have shortcomings either in terms of flexibility or performance. In addition, some of them depend on specific runtime environments and dictate the program's architecture. We present JAVADAPTOR, the first runtime update approach based on Java that (a) offers flexible dynamic software updates, (b) is platform independent, (c) introduces only minimal performance overhead, and (d) does not dictate the program architecture. JAVADAPTOR combines schema changing class replacements by class renaming and caller updates with Java HotSwap using containers and proxies. It runs on top of all major standard Java virtual machines. We evaluate our approach's applicability and performance in non-trivial case studies and compare it with existing dynamic software update approaches. Copyright

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Delegation is an important design concept in object-oriented languages. In contrast to inheritance, which relates classes to each other, delegation operates on the level of objects and thus provides more flexibility. It is well known, that usage of delegation imposes performance penalties in the sense of delayed execution. But delegation on the level of sourcecode is optimized on bytecode level up to a degree, that imposes much lower performance penalties than expected. This paper examines in detail how big these penalties are.