Understanding Code Smells in Android Applications

Code smells are associated with poor coding practices that cause long-term maintainability problems and mask bugs. Despite mobile being a fast growing software sector, code smells in mobile applications have been understudied. We do not know how code smells in mobile applications compare to those in desktop applications, and how code smells are affecting the design of mobile applications. Without such knowledge, application developers, tool builders, and researchers cannot improve the practice and state of the art of mobile development. We first reviewed the literature on code smells in Android applications and found that there is a significant gap between the most studied code smells in literature and most frequently occurring code smells in real world applications. Inspired by this finding, we conducted a large scale empirical study to compare the type, density, and distribution of code smells in mobile vs. desktop applications. We analyze an open-source corpus of 500 Android applications (total of 6.7M LOC) and 750 desktop Java applications (total of 16M LOC), and compare 14,553 instances of code smells in Android applications to 117,557 instances of code smells in desktop applications. We find that, despite mobile applications having different structure and workflow than desktop applications, the variety and density of code smells is similar. However, the distribution of code smells is different - some code smells occur more frequently in mobile applications. We also found that different categories of Android applications have different code smell distributions. We highlight several implications of our study for application developers, tool builders, and researchers.