Java Method Calls in the Hierarchy - Uncovering Yet another Inheritance Foible

This paper describes an empirical investigation into method calls between classes at each level of the inheritance hierarchy in four, Java open source systems. We distinguish between method calls made to super classes in the hierarchy and external method calls made outside the line of super classes to the root. The premise on which the research rests is that classes should predominantly make use of super class functionality (as theory suggests) and relatively infrequent use of functionality outside those super classes. Results revealed that the most method calls were made to the methods of the classes where the majority of functionality resided (at shallow hierarchical levels) and not necessarily to the super classes of a class. The evidence presented therefore implies that developers are not using inheritance in the spirit originally intended and lends weight to the growing belief that OO inheritance has more practical foibles than theoretically stated advantages.