Lambda Refactoring in Practice

📜 Abstract

Refactoring is a technique to restructure code in order to improve its readability, maintainability, and extensibility, while preserving its behavior. This paper reports on our experience with a new refactoring—lambda refactoring—to transform existing Java code to take advantage of lambda expressions. Specifically, this refactoring transforms anonymous classes, inner classes, and functional interfaces into functionally equivalent lambda expressions. The refactoring saves developers' time to manually transform existing code to use lambda expressions. We also created a refactoring tool that performs this transformation automatically. We evaluated the usability and correctness of our tool on 16 open-source projects comprising 2,431 KLOC. Our results show that 81% of the refactorings are accepted by developers, 92.4% are correct, and the time savings can be significant—the tool reduces the transformation time from 15 minutes to 2 seconds. However, challenges remain because some transformations require semantic preservation or context-sensitive checks.