An Empirical Study of Software Refactorings in Real-World Open-Source Java Projects

Software refactoring is widely conducted in the industry and well-studied in the academic community. There are dozens of software refactoring types, and each type of refactoring often requires its unique tool support and algorithms. Consequently, knowing which types of refactorings are popular in real-world practice and which are less supported by existing tools is highly valuable. To this end, in this paper, we present a large-scale empirical study on software refactorings in real-world open-source Java projects. We first retrieved by keywords 15,860 code commits from GitHub that might contain software refactorings. From the resulting commits, we manually analyzed 1,200 of them and successfully identified 100 types of refactorings from 420 commits. We built a taxonomy for the discovered refactorings, and compared them against the refactoring types supported by state-of-the-art refactoring engines and miners. The comparison results suggest that 61 out of the 100 refactoring types have not yet been explicitly supported by any of the refactoring engines, and any refactoring miners have not explicitly supported 62. The empirical study has identified and revealed 31 under-explored refactorings observed in Java real-world open-source applications but not yet supported by existing refactoring tools. These refactorings may have implications for the development of future tool support and enhancements in the refactoring ecosystem.