Are unreachable methods harmful? Results from a controlled experiment

In this paper, we present the results of a controlled experiment conducted to assess whether the presence of unreachable methods in source code affects source code comprehensibility and modifiability. A total of 47 undergraduate students at the University of Basilicata participated in this experiment. We divided the participants in two groups. The participants in the first group were asked to comprehend code base containing unreachable methods and implement five change requests in that code base. The participants in the second group were asked to accomplish exactly the same tasks as the participants in the first group, however, the source code provided to them did not contain any unreachable methods. The results of the study indicate that code comprehensibility is significantly higher when source code does not contain unreachable methods. However, we did not observe a statistically significant difference for code modifiability. From these results, we distill lessons and implications for practitioners as well as possible avenues for further research.