Refactoring for Parameterizing Java Classes

TL;DR: A type- constraint-based algorithm for converting non-generic libraries to add type parameters, which handles the full Java language and preserves backward compatibility, thus making it safe for existing clients.

Abstract: Type safety and expressiveness of many existing Java libraries and their client applications would improve, if the libraries were upgraded to define generic classes. Ef- ficient and accurate tools exist to assist client applications to use generic libraries, but so far the libraries themselves must be parameterized manually, which is a tedious, time-consuming, and error-prone task. We present a type-constraint- based algorithm for converting non-generic libraries to add type parameters. The algorithm handles the full Java language and preserves backward compatibility, thus making it safe for existing clients. Among other features, it is capable of inferring wildcard types and introducing type parameters for mutually-dependent classes. We have implemented the algorithm as a fully automatic refactoring in Eclipse. We evaluated our work in two ways. First, our tool parameterized code that was lacking type parameters. We contacted the developers of several of these applications, and in all cases they confirmed that the resulting parameterizations were correct and useful. Second, to better quantify its effectiveness, our tool parameterized classes from already-generic libraries, and we compared the results to those that were created by the libraries' authors. Our tool performed the refactoring accurately.in 87% of cases the results were as good as those created manually by a human expert, in 9% of cases the tool results were better, and in 4% of cases the tool results were worse.