What are the characteristics of popular APIs? A large-scale study on Java, Android, and 165 libraries

摘要

Abstract Software systems are commonly implemented with the support of libraries, which provide features via APIs. Ideally, APIs should have some characteristics, for example, they should be well documented and stable so that client systems can confidently rely on them. However, not all APIs are equal in number of clients: while some APIs are very popular and used worldwide, other may face much lower usage rates. In this context, one question appears: are there particular characteristics that differentiate popular APIs from ordinary APIs? Answering this question can uncover how worldwide APIs are actually implemented and maintained, revealing practices to better support both research and development on APIs. In this paper, we assess the characteristics of popular APIs, including their size, legibility, documentation, stability, and client adoption. We analyze 1491 APIs provided by Java, Android, and 165 libraries. We detect that popular APIs are distinct from ordinary ones, for example, often, popular APIs are larger, have more comments, and are more unstable than ordinary APIs. Finally, we provide a set of lessons learned from the popular APIs on factors that developers can control, such as the exposure of public methods and the API stability.