Revealing Purity and Side Effects on Functions for Reusing Java Libraries

Jiachen Yang, Keisuke Hotta, Yoshiki Higo, Shinji Kusumoto

Abstract: Reuse of software components requires the comprehension of the behavior and possible side effects among APIs of program components. Meanwhile, identifying problematic usage of these components is difficult with conventional static analysis. Purity and side effects are important properties of methods that often are neglected by the documentations of the object oriented languages such as Java. In this paper, we studied these properties by using a static analysis technique to automatically infer the state dependencies for the return value and side effects of methods. As a result, the effect information reveals purity of methods as well as well-defined state interactions between objects. We have implemented the analyzer targeting Java bytecode and tested it on some open source Java software libraries with different scale and characteristic. From our experimental results, we found that 24–44% of the methods in the evaluated open source Java libraries are pure, which indicates that a large percentage of the methods are suitable for high level refactoring. Our study can help programmers to understand and reuse these libraries.