Inferring Specications of Object Oriented APIs from API Source Code

API libraries are becoming increasingly popular in mod-ern software industries because these libraries provide var-ious methods and classes for reuse. However, as pointed out by researchers, libraries are typically difcult to use. It is desirable to infer some specications for libraries so that programmers can learn the correct usages of these li-braries. In this paper, we propose an approach to infer specications from source code of API libraries. Our ap-proach is based on the observation that rules in object-oriented programs can be traced from basic constraints such as memory usage, le usage, and network protocol. In addition, rules of one class spread to its dependent classes through the features of object-oriented programs such as derivation, invocation relationship, and eld access among methods. Based on our approach, we implemented a proto-type named Java Rule Finder (JRF) to infer specications from source code of API libraries in Java. We conducted four case studies using JRF. The result shows that JRF in-fers some rules correctly. We further conducted an experi-ment on three open source API libraries. The results show that JRF scales well with real API libraries.