Should we beware the inheritance? An empirical study on the evolution of seven open source systems

One of the key mechanisms of object-oriented programming is inheritance. Some empirical studies show that classes inheriting behavior from more classes (i.e., ancestors) are more defect prone than the other classes. Since various collaborations are found among the instances of classes, classes are not isolated within the source code of object-oriented systems. In this paper, we investigate if classes using classes inheriting behaviour from other classes are more change and defect prone than the other classes. We analyze at least three releases of every system belonging to a suite of seven open source systems and investigate the relations between classes that use/do not use class hierarchies and study the change and defect proneness of those classes. The results frequently show that the clients of classes which inherit behaviour are more change and defect prone. These findings show a new type of correlation between the clients of class hierarchies and changes/defects, bringing evidence related to an increased likelihood of exhibiting changes and defects for the clients of class hierarchies. We believe that the inferred correlations are due to an improper usage of class hierarchies but further studies are needed for confirmation.