In order to increase the maintainability and the flexibility of a software, its design and implementation quality must be properly assessed. For

Polymorphism and class hierarchies are key to increasing the extensibility of an object-oriented program but also raise challenges for program comprehension. Despite many advances in understanding and restructuring class hierarchies, there is no direct support to analyze and understand the design decisions that drive their polymorphic usage. In this paper we introduce a metric-based visual approach to capture the extent to which the clients of a hierarchy polymorphically manipulate that hierarchy. A visual pattern vocabulary is also presented in order to facilitate the communication between analysts. Initial evaluation shows that our techniques aid program comprehension by effectively visualizing large quantities of information, and can help detect several design problems.

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Object-oriented legacy systems are hard to maintain because they are hard to understand. One of the main understanding problems is revealed by the so-called "yo-yo effect" that appears when a developer or maintainer wants to track a polymorphic method call. At least part of this understanding problem is due to the dual nature of the inheritance relation i.e., the fact that it can be used both as a code and/or as an interface reuse mechanism. Unfortunately, in order to find out the original intention for a particular hierarchy it is not enough to look at the hierarchy itself; rather than that, an in-depth analysis of the hierarchy's clients is required. In this paper we introduce a new metrics-based approach that helps us characterize the extent to which a base class was intended for interface reuse, by analyzing how clients use the interface of that base class. The idea of the approach is to quantify the extent to which clients treat uniformly the instances of the descendants of the base class, when invoking methods belonging to this common interface. We have evaluated our approach on two medium-sized case studies and we have found that the approach does indeed help to characterize the nature of a base class with respect to interface reuse. Additionally, the approach can be used to detect some interesting patterns in the way clients actually use the descendants through the interface of the base class.