An Empirical Evaluation of Impact of Refactoring On Internal and External Measures of Code Quality

Refactoring is the process of improving the design of existing code by changing its internal structure without affecting its external behaviour, with the main aims of improving the quality of software product. Therefore, there is a belief that refactoring improves quality factors such as understandability, flexibility, and reusability. However, there is limited empirical evidence to support such assumptions. The objective of this study is to validate/invalidate the claims that refactoring improves software quality. The impact of selected refactoring techniques was assessed using both external and internal measures. Ten refactoring techniques were evaluated through experiments to assess external measures: Resource Utilization, Time Behaviour, Changeability and Analysability which are ISO external quality factors and five internal measures: Maintainability Index, Cyclomatic Complexity, Depth of Inheritance, Class Coupling and Lines of Code. The result of external measures did not show any improvements in code quality after the refactoring treatment. However, from internal measures, maintainability index indicated an improvement in code quality of refactored code than non-refactored code and other internal measures did not indicate any positive effect on refactored code.