MORE: A multi-objective refactoring recommendation approach to introducing design patterns and fixing code smells

Refactoring is widely recognized as a crucial technique applied when evolving object-oriented software systems. If applied well, refactoring can improve different aspects of software quality including readability, maintainability and extendibility. However, despite its importance and benefits, recent studies report that automated refactoring tools are underused much of the time by software developers. This paper introduces an automated approach for refactoring recommendation, called MORE, driven by three objectives: (1) to improve design quality (as defined by software quality metrics), (2) to fix code smells, and (3) to introduce design patterns. To this end, we adopt the recent non-dominated sorting genetic algorithm, NSGA-III, to find the best trade-off between these three objectives. We evaluated the efficacy of our approach using a benchmark of seven medium and large open-source systems, seven commonly-occurring code smells (god class, feature envy, data class, spaghetti code, shotgun surgery, lazy class, and long parameter list), and four common design pattern types (visitor, factory method, singleton and strategy). Our approach is empirically evaluated through a quantitative and qualitative study to compare it against three different state-of-the art approaches, two popular multi-objective search algorithms, as well as random search. The statistical analysis of the results confirms the efficacy of our approach in improving the quality of the studied systems while successfully fixing 84% of code smells and introducing an average of six design patterns. In addition, the qualitative evaluation shows that most of the suggested refactorings (an average of 69%) are considered by developers to be relevant and meaningful. Copyright c © 2017 John Wiley & Sons, Ltd.