Do code clones matter?

Empirical Software …, 2010

Code clones are exactly or nearly similar code fragments in the code-base of a software system. Existing studies show that clones are directly related to bugs and inconsistencies in the code-base. Code cloning (making code clones) is suspected to be responsible for replicating bugs in the code fragments. However, there is no study on the possibilities of bug-replication through cloning process. Such a study can help us discover ways of minimizing bug-replication. Focusing on this we conduct an empirical study on the intensities of bug-replication in the code clones of the major clone-types: Type 1, Type 2, and Type 3.

Code cloning is a recurrent operation in everyday software development. Whether it is a good or bad practice is an ongoing debate among researchers and developers for the last few decades. In this paper, we conduct a comparative study on bugproneness in clone code and non-clone code by analyzing commit logs. According to our inspection on thousands of revisions of seven diverse subject systems, the percentage of changed files due to bug-fix commits is significantly higher in clone code compared with non-clone code. We perform a Mann-Whitney-Wilcoxon (MWW) test to show the statistical significance of our findings. Finally, the possibility of severe bugs occurring is higher in clone code than in non-clone code. Bug-fixing changes affecting clone code should be considered more carefully. According to our findings, clone code appears to be more bug-prone than non-clone code.

2008

Existing software systems contain a significant amount of duplicated code. Such redundancy can negatively impact program correctness, since inconsistent updates to duplicated code fragments are prone to introduce subtle bugs. This paper outlines our work-in-progress to statically detect inconsistencies in duplicated code fragments in order to find clone-related bugs. We illustrate the problem of clone related bugs with the example of such a bug in Eclipse, outline our algorithm for detecting inconsistencies in clones and report initial experiences from an industrial case study conducted with the Munich Re Group.

2010

There are numerous studies that examine whether or not cloned code is harmful to software systems. Yet, few of them study which characteristics of cloned code in particular lead to software defects. In our work, we use survival analysis to understand the impact of clones on software defects and to determine the characteristics of cloned code that have the highest impact on software defects. Our survival models express the risk of defects in terms of basic predictors inherent to the code (e.g., LOC) and cloning predictors (e.g., number of clone siblings). We perform a case study using two clone detection tools on two large, long-lived systems using survival analysis. We determine that the defect-proneness of cloned methods is specific to the system under study and that more resources should be directed towards methods with a longer 'commit history'.

2003

Abstract Code cloning—that is, the gratuitous duplication of source code within a software system—is an endemic problem in large, industrial systems [9, 7]. While there has been much research into techniques for clone detection and analysis, there has been relatively little empirical study on characterizing how, where, and why clones occur in industrial software systems.

Code cloning is a recurrent operation in everyday software development. Whether it is a good or bad practice is an ongoing debate among researchers and developers for the last few decades. In this paper, we conduct a comparative study on bug-proneness in clone code and non-clone code by analyzing commit logs. According to our inspection of thousands of revisions of seven diverse subject systems, the percentage of changed¯les due to bug-¯x commits is signi¯cantly higher in clone code compared with non-clone code. We perform a Mann-Whitney-Wilcoxon (MWW) test to show the statistical signi¯cance of our¯ndings. In addition, the possibility of occurrence of severe bugs is higher in clone code than in non-clone code. Bug-¯xing changes a®ecting clone code should be considered more carefully. Finally, our manual investigation shows that clone code containing if-condition and if-else blocks has a high risk of having severing bugs. Changes to such types of clone fragments should be done carefully during software maintenance. According to our¯ndings, clone code appears to be more bug-prone than non-clone code.

2006

Abstract Code duplication is a well-documented problem in industrial software systems. There has been considerable research into techniques for detecting duplication in software, and there are several effective tools to perform this task. However, there have been few detailed qualitative studies into how cloning actually manifests itself within software systems.

Over the last decade many techniques and tools for software clone detection have been proposed. In this paper, we provide a qualitative comparison and evaluation of the current state-of-the-art in clone detection techniques and tools, and organize the large amount of information into a coherent conceptual framework. We begin with background concepts, a generic clone detection process and an overall taxonomy of current techniques and tools. We then classify, compare and evaluate the techniques and tools in two different dimensions. First, we classify and compare approaches based on a number of facets, each of which has a set of (possibly overlapping) attributes. Second, we qualitatively evaluate the classified techniques and tools with respect to a taxonomy of editing scenarios designed to model the creation of Type-1, Type-2, Type-3 and Type-4 clones. Finally, we provide examples of how one might use the results of this study to choose the most appropriate clone detection tool or technique in the context of a particular set of goals and constraints. The primary contributions of this paper are: (1) a schema for classifying clone detection techniques and tools and a classification of current clone detectors based on this schema, and (2) a taxonomy of editing scenarios that produce different clone types and a qualitative evaluation of current clone detectors based on this taxonomy.

The new hybrid clone detection tool NICAD combines the strengths and overcomes the limitations of both text-based and AST-based clone detection techniques and exploits novel applications of a source transformation system to yield highly accurate identification of cloned code in software systems. In this paper, we present an in-depth study of near-miss function clones in open source software using NICAD. We examine more than 20 open source C, Java and C# systems, including the entire Linux Kernel, Apache httpd, J2SDK-Swing and db4o and compare their use of cloned code in several different dimensions, including language, clone size, clone similarity, clone location and clone density both by proportion of cloned functions and lines of cloned code. We manually verify all detected clones and provide a complete catalogue of different clones in an online repository in a variety of formats. These validated results can be used as a cloning reference for these systems and as a benchmark for evaluating other clone detection tools.