The evolution and impact of code smells: A case study of two open source systems

Code smells are design flaws in object-oriented designs that may lead to maintainability issues in the further evolution of the software system. This study focuses on the evolution of code smells within a system and their impact on the change behavior (change frequency and size). The study investigates two code smells, God Class and Shotgun Surgery, by analyzing the historical data over several years of development of two large scale open source systems. The detection of code smells in the evolution of those systems was performed by the application of an automated approach using detection strategies. The results show that we can identify different phases in the evolution of code smells during the system development and that code smell infected components exhibit a different change behavior. This information is useful for the identification of risk areas within a software system that need refactoring to assure a future positive evolution.