Towards purity-guided refactoring in Java

Refactoring source code requires preserving a certain level of semantic behaviors, which are difficult to be checked by IDEs. Therefore, IDEs generally check syntactic pre-conditions instead before applying refactoring, which are often too restrictive than checking semantic behaviors. On the other hand, there are pure functions in the source code that do not have observable side-effects, of which semantic behaviors are more easily to be checked. In this research, we propose purity-guided refactoring, which applies high-level refactoring such as memoization on pure functions that can be detected statically. By combining our purity analyzing tool purano with refactoring, we can ensure the preservation of semantic behaviors on these detected pure functions, which is impossible through previous refactoring operations provided by IDEs. As a case study of our approach, we applied memorization refactoring on several open-source software in Java. We observed improvements of the performance and preservation of semantics by profiling their bundled test cases.