Unifying clones with a generative programming technique: a case study

Abstract

Software clones-similar program structures repeated in variant forms-increase the risk of update anomalies, blow up the program size and complexity, possibly contributing to high maintenance costs. Yet, programs are often polluted by clones. In this paper, we present a case study of cloning in the Java Buffer library, JDK 1.5. We found that at least 68% of the code in the Buffer library was contained in cloned classes or class methods. Close analysis of program situations that led to cloning revealed difficulties in eliminating clones with conventional program design techniques. As a possible solution, we applied a generative technique of XVCL (XML-based Variant Configuration Language) to represent similar classes and methods in generic, adaptable form. Concrete buffer classes could be automatically produced from the generic structures. We argue, on analytical and empirical grounds, that unifying clones reduced conceptual complexity and enhanced the changeability of the Buffer library at rates proportional to code size reduction (68%). We evaluated our solution in qualitative and quantitative ways, and conducted a controlled experiment to support this claim. The approach presented in the paper can be used to enhance genericity and changeability of any program, independently of an application domain or programming language. As the solution is not without pitfalls, we discuss trade-offs involved in its project application.

An Exploratory Study of Cloning in Industrial Software Product Lines

“…Although clones were initially considered undesirable [27], multiple authors later argued that this assumption is not necessarily true and reported corresponding empirical data. Kapser and Godfrey [28] describe several observed patterns of cloning and provide evidence that cloning is used as a principled engineering technique.…”

Genericity - a "Missing in Action" Key to Software Simplification and Reuse

“…Generics could unify 15 among 74 classes under study, reducing the code size by 27%. The solution with generics was subject to certain restrictions that we discussed in [17].…”

“…The number of modifications to implement Complex buffer in a mixed-strategy representation was 11, as compared to 91 modifications required for the same purpose in the original Buffer library. Further details of this study are described in [17].…”

“…For example, the extent of similarities in Java Buffer library was 68% [17], in Web Portal (J2EE) -68% [27], and in certain ASP Web Portal modules -up to 90% [24]. A survey of 17 Web Applications revealed 17-60% of code contained in clones [25].…”

Frontiers of software clone management

“…The use of design patterns is another option to avoid clones by better design [11,12] although this approach can hardly be automated. Likewise, one can develop code generators for highly repetitive code [39].…”