Playing roles in design patterns: an empirical descriptive and analytic study

This work presents a descriptive and analytic studyof classes playing zero, one, or two roles in six differentdesign patterns (and combinations thereof ). First, weanswer three research questions showing that (1) playing roles in design patterns is not a all-or-nothing characteristic of classes and that there are significant differences among the (2) internal and (3) external characteristics of classes playing zero, one, or two roles.Second, we revisit a previous work on design patternsand changeability and show that its results were, in agreat part, due to classes playing two roles. Third, weexemplify the use of the study results to provide a ranking of the occurrences of the design patterns identifiedin a program. The ranking allows developers to balanceprecision and recall as they see fit.