Um estudo quantitativo sobre o uso de herança e interface em sistemas Java

Abstract

Inheritance is one of the main features in the object-oriented paradigm (OOP). Nonetheless, previous work recommend carefully using it, suggesting alternatives in Java such as the adoption of composition with implementation of interfaces. Despite of being a well-studied theme, there is still little knowledge if such recommendations have been widely adopted by developers in general. This work aims at evaluating how the inheritance and interface resources have been used in Java, comparing new projects with older ones, and also the different releases of projects. Evaluated indicators were the number of corrective changes of the projects, encapsulation breaks by the use of instanceof operator, measures of cohesion, coupling and occurrence of code smells. We also studied how often inheritance or interface features are added or removed from classes, and motivations by which developers perform such procedure. A total of 1,656 open-source projects built between 1997 and 2013, all hosted in the repositories GitHub and SourceForge, were analyzed. We observed developers still use inheritance primarily as a resource for code reuse, motivated by the need to avoid duplicity of source code. In newer projects, classes in inheritance hierarchy had fewer corrective changes and subclasses had fewer use of the instanceof operator. However, as they evolve, classes in inheritance hierarchy tend to become complex as changes occur. Classes implementing interfaces have shown little relation to the interfaces, and there is indication that they are still underutilized. These results show there is still some lack of knowledge about the use of adequate object- oriented practices, which reinforces the need for training developers on how to design better classes.