Automated support for program refactoring using invariants

Program refactoring — transforming a program to improve readability, structure, performance, abstraction, maintain-ability, or other features — is not applied in practice as much as might be desired. One deterrent is the cost of detecting candidates for refactoring and of choosing the appropriate refactoring transformation. This paper demonstrates the fea-sibility of automatically finding places in the program that are candidates for specific refactorings. The approach uses program invariants: when a particular pattern of invariant relationships appears at a program point, a specific refac-toring is applicable. Since most programs lack explicit in-variants, an invariant detection tool called Daikon is used to infer the required invariants. We developed an invariant pat-tern matcher for several common refactorings and applied it to an existing Java code base. Numerous refactorings were detected, and one of the developers of the code base assessed their efficacy.