Encapsulating objects with confined types

Object-oriented languages provide little support for encapsulating objects. Reference semantics allows objects to escape their defining scope, The pervasive aliasing that ensues remains a major source of software defects. This paper introduces Kacheck/J a tool for inferring object encapsulation properties in large Java programs. Our goal is to develop practical tools to assist software engineers, thus we focus on simple and scalable techniques. Kacheck/J is able to infer confinement for Java classes. A class and its subclasses are confined if all of their instances are encapsulated in their defining package. This simple property can be used to identify accidental leaks of sensitive objects. The analysis is scalable and efficient; Kacheck/J is able to infer confinement on a corpus of 46,000 classes (115 MB) in 6 minutes.