Broken Windows: Exploring the Applicability of a Controversial Theory on Code Quality

Is the quality of existing code correlated with the quality of subsequent changes? According to the (controversial) broken windows theory, which inspired this study, disorder sets descriptive norms and signals behavior that further increases it. From a large code corpus, we examine whether code history does indeed affect the evolution of code quality. We examine C code quality metrics and Java code smells in specific files, and see whether subsequent commits by developers continue on that path. We check whether developers tailor the quality of their commits based on the quality of the file they commit to. Our results show that history matters, that developers behave differently depending on some aspects of the code quality they encounter, and that programming style inconsistency is not necessarily related to structural qualities. These findings have implications for both software practice and research. Software practitioners can emphasize current quality practices as these influence the code that will be developed in the future. Researchers in the field may replicate and extend the study to improve our understanding of the theory and its practical implications on artifacts, processes, and people.