An Empirical Study into Use of Dependency Injection in Java

Over the years many guidelines have been offered as to how to achieve good quality designs. We would like to be able to determine to what degree these guidelines actually help. To do that, we need to be able to determine when the guidelines have been followed. This is often difficult as the guidelines are often presented as heuristics or otherwise not completely specified. Nevertheless, we believe it is important to gather quantitative data on the effectiveness of design guidelines wherever possible. In this paper, we examine the use of "dependency injection", which is a design principle that is claimed to increase software design quality attributes such as extensibility, modifiability, testability, and reusability. We develop operational definitions for it and analysis techniques for detecting its use. We demonstrate these techniques by applying them to 34 open source Java applications.