Characterising the Knowledge about Primitive Variables in Java Code Comments

TL;DR

This study introduces an advanced method for detecting and analyzing comments about primitive variables in Java code, revealing that developers document numeric types more thoroughly than String or boolean types.

Contribution

The paper presents a novel approach combining lexical and advanced matching to accurately identify and classify comments about primitive variables in source code.

Findings

Advanced matching outperforms lexical matching in detection accuracy

Developers more frequently document purpose and concept for numeric variables

Boolean variables and certain fields are less well documented

Abstract

Primitive types are fundamental components available in any programming language, which serve as the building blocks of data manipulation. Understanding the role of these types in source code is essential to write software. Little work has been conducted on how often these variables are documented in code comments and what types of knowledge the comments provide about variables of primitive types. In this paper, we present an approach for detecting primitive variables and their description in comments using lexical matching and advanced matching. We evaluate our approaches by comparing the lexical and advanced matching performance in terms of recall, precision, and F-score, against 600 manually annotated variables from a sample of GitHub projects. The performance of our advanced approach based on F-score was superior compared to lexical matching, 0.986 and 0.942, respectively. We then create a taxonomy of the types of knowledge contained in these comments about variables of primitive types. Our study showed that developers usually documented the variables' identifiers of a numeric data type with their purpose~(69.16%) and concept~(72.75%) more than the variables' identifiers of type String which were less documented with purpose~(61.14%) and concept~(55.46%). Our findings characterise the current state of the practice of documenting primitive variables and point at areas that are often not well documented, such as the meaning of boolean variables or the purpose of fields and local variables.