Influencing Factors on the Usability of API Classes and Methods

Usability is an important quality attribute for APIs. To create APIs with good usability, appropriate measurement methods are needed. But currently available methods are cost- and time-expensive and the results are not objective and therefore hard to quantify. API design guidelines give a good overview about important usability factors, but lack a scientific basis. When looking at scientific API usability studies, only a very small area of API design has been researched yet. Existing results don´t give enough basis for a good API usability measurement method. In this paper we identify influencing usability factors for the two most common concepts of APIs: classes and methods. We therefore conduct a study with 20 programmers and 2 different API variants and evaluate how differences between the APIs influence usability when instantiating classes and calling methods. The results build a basis for API usability measurement methods and should help design more usable APIs.