Co-occurrence analysis of design patterns and bad smells in software systems

Abstract

Software systems are often developed in a way that good practices of the object-oriented paradigm are not fulfilled, causing the occurrence of bad smells. Bad smells are symptoms or structural characteristics in a region of code that may suggest the presence of a deeper problem in the system design or code. On the other hand, design patterns are intended to catalog the best practices for developing object-oriented software systems. Although apparently widely divergent, there may be a co-occurrence of design patterns and bad smells, since this phenomenon is sometimes cited in studies in the software engineeringfield, albeit discreetly. Therefore, this dissertation performs an exploratoryanalysis in order to identify the co-occurrence of design patterns and bad smells in software systems, that may happen due to the inadequate use of design patterns. To achieve this goal, we first perform a literature review in order to understand the current state of art concerning design patterns and bad smells and, then, we accomplish an exploratory study to identify concrete instances of design patterns inadequate usagethat lead to bad smells occurrences. In this study, we use tools for detecting design patterns and bad smells in five medium to large size systems. The study results indicate interesting co-occurrences, as Command with God Class and Template Method with Duplicated Code. We analyse why these patterns provoked the bad smells arising. Wealso discuss the severity of bad smells and, when appropriate, propose changes to the system code in order to address the detected bad smells. These findings indicate that, although design patterns catalog the best practices for developing software systems, their inadequate use may have undesired effects.