Visual Detection of Duplicated Code

Code duplication is considered as bad practice that complicates the maintenance and evolution of software. Detecting duplicated code is a difficult task because of the large amount of data to be checked and the fact that a priori it is unknown which code part has been duplicated. In this paper, we present a tool called DUPLOC that supports code duplication detection in a visual and exploratory or an automatic way. 1 Why we need to deal with Duplicated Code Duplicated code is a phenomenon that occurs frequently in large systems. Although duplication can have its justifications, it is considered bad practice. The reasons programmers duplicate code are multi-fold [Bak95] : making a copy of a code fragment is simpler and faster than writing the code from scratch and, in addition, the fragment may already be tested so the introduction of a bug seems less likely. Efficiency considerations may make the cost of a procedure call seem too high a price. In reverse engineering, we are interested in detecting and subsequently removing unjustified duplicated code for the following reasons: Removing bugs. If one is sure that the code segment where a bug is found occurs only once in the system, one can be confident that the bug has been eradicated from the system. This work has been funded by the Swiss Government under Project no. NFS-2000-46947.96 and BBW96.0015 as well as by the European Union under the ESPRIT program Project no. 21975.