Mario Fusco Lets make a contract the art of designing a Java API

An API is what developers use to achieve some task. More precisely it establishes a contract between them and the designers of the software exposing its services through that API. In this sense we re all API designers: our software doesn t work in isolation, but becomes useful only when it interacts with other software written by other developers. When writing software we re not only consumers, but also providers of one or more API and that s why every developer should know the features of a good API. During this presentation we will go through realworld examples, also taken from the standard Java API, of good and bad API and comment them in order to show the dos and don ts of API design. More in general we will discuss the characteristics of an easy and pleasant to use API, like consistency, discoverability and understandability, together with some basic concepts like the principle of least astonishment, and find out how to achieve them.