An Empirical Study of Java System Evolution at the Method Level

Exploring the evolution of systems can provide valuable insights into the traits of developers and inform our understanding of system dynamics. While we usually expect an object-oriented system to grow (in classes) as it ages, what are not so obvious are patterns in the evolution of specific class features. In this paper, we explore empirical traits of four Java open-source systems using data extracted by two tools and informed by a previous study of inheritance depth evolution. We analyse evolution at a lower level of granularity given by the `methods´ of a class on an incremental (change per version) basis rather than absolute class size per version. Evolution at a finer-grain can identify trends not possible on a class-wide basis; the approach thus represents a `white-box´ view of the investigation of evolutionary forces. Our analysis also allowed direct comparison with a set of low-level refactorings extracted by an automated tool in a previous study. Scrutiny of trends in methods was further motivated by the fact that the vast majority of refactorings apply not at the class level but at the method level.