Coupling, code reuse and open implementation in reflective systems

Little research has been conducted in investigating the implications of employing reflection in object-oriented (OO) systems on software qualities such as coupling and reuse. In this thesis, we investigate the reflective capabilities of Java as a representative of mainstream OO languages and propose a behavioural reflection model, which complements the language's inextensible, introspective, structural reflection model. We show that reflective systems based on the proposed model support the principle of open implementation, and exhibit less coupling and a higher level of code reuse. Programming examples explain how the behaviour of such systems can be customised or adapted without changing their default behaviour or structure. We then show that the model is also applicable to distributed systems allowing for generic coding on the server side. We address the question of assessing coupling and code reuse qualities of reflective systems quantitatively. For this purpose, we define a dynamic coupling metric and a measuring tool that allows the collection of object coupling data at runtime. A case study shows that our coupling metric can be measured automatically and confirms the hypothesis about the relatively low coupling of reflective systems in comparison with equivalent systems based on the classical non-reflective programming model. As for code reuse, we define OO reuse metrics by extending a set of metrics previously developed for procedural languages. A case study is used to confirm the hypothesis that reflective systems are more reusable than non-reflective systems exhibiting the same behaviour.