Class movement and re-location: An empirical study of Java inheritance evolution

Abstract

Inheritance is a fundamental feature of the Object-Oriented (OO) paradigm. It is used to promote extensibility and reuse in OO systems. Understanding how systems evolve, and specifically, trends in the movement and re-location of classes in OO hierarchies can help us understand and predict future maintenance effort. In this paper, we explore how and where new classes were added as well as where existing classes were deleted or moved across inheritance hierarchies from multiple versions of four Java systems. We observed first, that in one of the studied systems the same set of classes was continuously moved across the inheritance hierarchy. Second, in the same system, the most frequent changes were restricted to just one sub-part of the overall system. Third, that a maximum of three levels may be a threshold when using inheritance in a system; beyond this level very little activity was observed, supporting earlier theories that, beyond three levels, complexity becomes overwhelming. We also found evidence of 'collapsing' hierarchies to bring classes up to shallower levels. Finally, we found that larger classes and highly coupled classes were more frequently moved than smaller and less coupled classes. Statistical evidence supported the view that larger classes and highly coupled classes were less cohesive than smaller classes and lowly coupled classes and were thus more suitable candidates for being moved (within an hierarchy).

An Analysis of Inheritance Hierarchy Evolution

“…The fifth column indicates the system problem domain. The number of systems, number of versions and the range of domains analysed are comparable to related work [12,13,17]. The range of system sizes is in keeping with system sizes found by Radjenović et al in a review of code-survey research -where less than 200 classes was categorised as a small system, 200-1000 classes medium sized, and 1000 or greater as large [14].…”

“…This had the tendency to increase the shallow breadth of hierarchies through time. In related research [13], Nasseri et al found that most of the inheritance changes were again in shallow areas of the hierarchies (level three or shallower) and that many of the changes led to a 'squashing' of the hierarchies.…”

The effect of multiple developers on structural attributes: A Study based on java software

“…shown that DIT values tend to be generally low and that, if anything, inheritance hierarchies will tend to collapse over time (becoming shallower) rather than deeper [56,52,57]. Typically, this leads to systems with low median DIT values of one or two, as Table 7 shows.…”

Multi-Paradigm Metric and its Applicability on JAVA Projects

“…In their comparison analysis, the authors also suggested which type of refactoring is required. In an another empirical study of JAVA inheritance evaluation, Nasseri et al [12] found that larger and highly coupled classes were less cohesive and more frequently moved than smaller and less coupled classes. Kaczmarek and Kucharski [13] demonstrated how to estimate size and efforts for JAVA based applications.…”