Patterns of Interface-Based Programming

Modern software architectures heavily promote the use of interfaces. Originally conceived as a means to separate specification from implementation, popular programming languages toady accommodate interfaces as special kinds of types that can be used - in place of classes - in variable declarations. While it is clear that these interfaces offer polymorphism independent of the inheritance hierarchy, little has been said about the systematic use of interfaces, or how they are actually used in practice. By providing a set of basic patterns of interface use together with numbers of their frequency we provide insights that should be of interest not only to the practising programmer, but also to the designers and analysts of large code bases.