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Comments are valuable especially for program understanding and maintenance, but do developers comment their code? To which extent do they add comments or adapt them when they evolve the code? We examine the question whether source code and associated comments are really changed together along the evolutionary history of a software system. In this paper, we describe an approach to map code and comments to observe their co-evolution over multiple versions. We investigated three open source systems (i.e., ArgoUML, Azureus, and JDT Core) and describe how comments and code co-evolved over time. Some of our findings show that: 1) newly added code|despite its growth rate|barely gets commented; 2) class and method declarations are commented most frequently but far less, for example, method calls; and 3) that 97% of comment changes are done in the same revision as the associated source code change.

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Abstract. Code clones have long been recognized as bad smells in software systems and are considered to cause maintenance problems during evolution. It is broadly assumed that the more clones two files share, the more often they have to be changed together. This relation between clones and change couplings has been postulated but neither demonstrated nor quantified yet. However, given such a relation it would simplify the identification of restructuring candidates and reduce change couplings. In this paper, we examine this relation and discuss if a correlation between code clones and change couplings can be verified. For that, we propose a framework to examine code clones and relate them to change couplings taken from release history analysis. We validated our framework with the open source project Mozilla and the results of the validation show that although the relation is statistically unverifiable it derives a reasonable amount of cases where the relation exists. Therefore, to discover clone candidates for restructuring we additionally propose a set of metrics and a visualization technique. This allows one to spot where a correlation between cloning and change coupling exists and, as a result, which files should be restructured to ease further evolution.