Does the Introduction of Lambda Expressions Improve the Comprehension of Java Programs?

Abstract

Background: The Java programming language version eighth introduced a number of features that encourage the functional style of programming, including the support for lambda expressions and the Stream API. Currently, there is a common wisdom that refactoring a legacy code to introduce lambda expressions, besides other potential benefits, simplifies the code and improves program comprehension. Aims: The purpose of this paper is to investigate this belief, conducting an in depth study to evaluate the effect of introducing lambda expressions on program comprehension. Method: We conduct this research using a mixed-method study. First, we quantitatively analyze 66 pairs of real code snippets, where each pair corresponds to the body of a method before and after the introduction of lambda expressions. We computed two metrics related to source code complexity (number of lines of code and cyclomatic complexity) and two metrics that estimate the readability of the source code. Second, we conduct a survey with practitioners to collect their perceptions about the benefits on program comprehension, with the introduction of lambda expressions. The practitioners evaluate a number between three and six pairs of code snippets, to answer questions about possible improvements. Results: We found contradictory results in our research. Based on the quantitative assessment, we could not find evidences that the introduction of lambda expressions improves software readability--one of the components of program comprehension. Differently, our findings of the qualitative assessment suggest that the introduction of lambda expression improves program comprehension. Implications: We argue in this paper that one can improve program comprehension when she applies particular transformations to introduce lambda expressions (e.g., replacing anonymous inner classes by lambda expressions). In addition, the opinion of the participants shine the opportunities in which a transformation for introducing lambda might be advantageous. This might support the implementation of effective tools for automatic program transformations. Finally, our results suggest that state-of-the-art models for estimating program readability are not helpful to capture the benefits of a program transformation to introduce lambda expressions.