Relating Complexity, Explicitness, Effectiveness of Refactorings and Non-Functional Requirements: A Replication Study

Refactoring is a practice widely adopted during software maintenance and evolution. Due to its importance, there is extensive work on the effectiveness of refactoring in achieving code quality. However, developer's intentions are usually overlooked. A more recent area of study involves the concept of self-affirmed refactoring (SAR), where developers explicitly state their intent to refactor. While studies on SAR have made valuable contributions, they provide little insights into refactoring complexity and effectiveness, as well as the refactorings' relations to specific non-functional requirements. A study by Soares et al. addressed such aspects, but it relied on a quite small sample of studied subject systems and refactoring instances. Following the empirical method of replication, we expanded the scope of Soares et al.'s study by doubling the number of projects analyzed and a significantly larger set of validated refactorings (8,408). Our findings only partially align with the original study. We observed that when developers explicitly state their refactoring intent, the resulting changes typically involve a combination of different refactoring types, making them more complex. Additionally, we confirmed that such complex refactorings positively impact code's internal quality attributes. While refactorings aimed at non-functional requirements tend to improve code quality, our findings only partially align with the original study and contradict it in several ways. Notably, SARs often result in fewer negative impacts on internal quality attributes despite their frequent complexity. These insights suggest the importance of simplifying refactorings where possible and explicitly stating their goals, as clear intent helps shape more effective and targeted refactoring strategies.