Using machine learning to guide the application of software refactorings: a preliminary exploration

Refactorings constitute the most direct and comprehensible ap-proach for addressing software quality issues, stemming directly from identified code smells. Nevertheless, despite their popularity in both the research and industrial communities: (a) the effect of a refactoring is not guaranteed to be successful; and (b) the plethora of available refactoring opportunities does not allow their compre-hensive application. Thus, there is a need of guidance, on when to apply a refactoring opportunity, and when the development team shall postpone it. The notion of interest, forms one of the major pil-lars of the Technical Debt metaphor expressing the additional maintenance effort that will be required because of the accumulated debt. To assess the benefits of refactorings and guide when a refac-toring should take place, we first present the results of an empirical study assessing and quantifying the impact of various refactorings on Technical Debt Interest (building a real-world training set) and use machine learning approaches for guiding the application of fu-ture refactorings. To estimate interest, we rely on the FITTED framework, which for each object-oriented class assesses its dis-tance from the best-quality peer; whereas the refactorings that are applied throughout the history of a software project are extracted with the RefactoringMiner tool. The dataset of this study involves 4,166 refactorings applied across 26,058 revisions of 10 Apache projects. The results suggest that the majority of refactorings reduce Technical Debt interest; however, considering all refactoring appli-cations, it cannot be claimed that the mean impact differs from zero, confirming the results of previous studies highlighting mixed ef-fects from the application of refactorings. To alleviate this problem, we have built an adequately accurate (~70%) model for the predic-tion of whether or not a refactoring should take place, in order to reduce Technical Debt interest.