Code Reuse in Stack Overflow and Popular Open Source Java Projects

Solutions provided in Question and Answer (Q&A) websites such as Stack Overflow are regularly used in Open Source Software (OSS). However, many developers are unaware that both Stack Overflow and OSS are governed by licenses. Hence, developers reusing code from Stack Overflow for their OSS projects may violate licensing agreements if their attributions are not correct. Additionally, if code migrates from one OSS through Stack Overflow to another OSS, then complex licensing issues are likely to exist. Such forms of software reuse also have implications for future software maintenance, particularly where developers have poor understanding of copied code. This paper investigates code reuse between these two platforms (i.e., Stack Overflow and OSS), with the aim of providing insights into this issue. This study mined 151,946 Java code snippets from Stack Overflow, 16,617 Java files from 12 of the top weekly listed projects on SourceForge and GitHub, and 39,616 Java files from the top 20 most popular Java projects on SourceForge. Our analyses were aimed at finding the number of clones (indicating reuse) (a) within Stack Overflow posts, (b) between Stack Overflow and popular Java OSS projects, and (c) between the projects. Outcomes reveal that there was up to 3.3% code reuse within Stack Overflow, while 1.0% of Stack Overflow code was reused in recent popular Java projects and 2.3% in those projects that were more established. Reuse across projects was much higher, accounting for as much as 77.2%. Our outcomes have implication for strategies aimed at introducing strict quality assurance measures to ensure the appropriateness of code reuse, and licensing requirements awareness.