How can Java packages be modified to better support large-scale software development? The authors offer nested inheritance and nested intersection as suitable modifications. An earlier paper covered nested inheritance [1]; this paper covers nested intersection.

Nested inheritance treats packages as a particular kind of class, and defines what it means to establish subclass-superclass relations among packages. Because packages can represent system components, establishing class relations among them creates framework hierarchies related by inheritance and overriding. Nested intersection extends nested inheritance by composing separate packages; because the hierarchies associated with each package are also composed, nested intersection represents a kind of multiple inheritance.

After motivating and describing objectives, the paper briefly presents nested inheritance and the improvements to it provided by nested intersection. Section 3 presents J&, an extension the Jx language to include nested intersection; Jx is Java extended to include nested inheritance [1]. Section 5 briefly covers the J& implementation, and sections 4 and 6 present practice and experience with J&, principally involving compilers and a framework for developing peer-to-peer systems.

This is a difficult paper. The authors’ experience with the Polyglot Java extension system [2] has significant influence on the problems and solutions dealt with in this paper. Without such experience, the reader must rely on sophisticated technical speculation, which reduces the potential audience for this paper, and risks misinterpreting the authors’ intent.