Recognition regarding code clones equivalent or similar source code fragments is of concern both to researchers along with to practitioners. An evaluation of the clone detection results for a single source code version gives a developer with details about a discrete state in the development of the software system.
Nevertheless, tracing clones throughout several source code versions enables a clone analysis to take into consideration a temporal dimension. This kind of an analysis of clone evolution may be utilized to find out the patterns as well as characteristics displayed by clones as they evolve within a system. Developers may utilize the outcomes of this analysis to recognize the clones more thoroughly, which may guide them to handle the clones more consequentially. Hence, studies of clone evolution provide a important role in perceiving as well as handling concerns of cloning in software.
This paper gives a systematic overview of the literature on clone evolution. Specifically, we give a complete analysis of 30 appropriate papers that we found as per our review protocol. The review outcomes are arranged to deal with three research questions. As a result of our outcomes to these questions, we provide the approaches that researchers have utilized to analyze clone evolution, the patterns that researchers have detected evolving clones to exhibit, as well as the data that researchers have established concerning the extent of conflicting adjustment gone through clones throughout software evolution. Overall, the review outcomes show that while researchers have carried out many bench marked studies of clone evolution, there are conflicts among the noted ﬁndings, specifically concerning the lifetimes of clone lineages as well as the persistence with which clones are modified throughout software evolution. We recognize human-based benchmarked studies along with classiﬁcation of clone evolution patterns as two areas in specifically require of further work.
Code clones are source code fragments that are resembling or equivalent in terms of text, vocabulary, structure, or meaning. Fowler et al.  classiﬁed code duplication (cloning), as a bad smell and therefore as a major indicator of poor software maintainability. Nevertheless, most latest work shows that clones are not as harmful as formerly assumed [2, 3] and also actually might increase productivity 
Indeed, Rahman et al.  ﬁnd minute benchmarked evidence that clones negatively impact software maintainability although do ﬁnd that cloned code may be less fault prone than non-cloned code. However, there are long term risks associated with cloning, like as the possible duplication of defects as well as the feasible loss of (implicit or explicit) links among code fragments that have to stay constant .
Hence, the research community persists to analyze code clones along with their descriptions. Two surveys published in 2007 give reviews of the code clone literature. Koschke...