Qualitative Analysis for the Impact of Accounting for Special Methods in Object-Oriented Class Cohesion Measurement

Class cohesion is a key object-oriented software quality attribute. It refers to the degree of relatedness of class attributes and methods. Several class cohesion metrics are proposed in the literature. However, the impact of considering the special methods (i.e., constructors, destructors, and access and delegation methods) in cohesion calculation is not thoroughly theoretically studied for most of the existing cohesion metrics. An incorrect determination of whether to include or exclude the special methods in cohesion measurement can lead to improper refactoring decisions according to the misleading class cohesion values that are obtained. In this paper, we qualitatively analyze the impact of including or excluding the special methods in cohesion measurement on the values that are obtained by applying 19 popular class cohesion metrics. The study is based on analyzing the definitions and formulas that are proposed for the metrics. The results show that including/excluding special methods has a considerable effect on the cohesion values that are obtained and that this effect varies from one metric to another. The study shows the importance of considering the types of methods that must be accounted for when proposing a cohesion metric.