By Atsushi Igarashi, Benjamin Pierce and Philip Wadler. ACM Transactions on Programming Languages and Systems, 23(3):396-450, May 2001.
A preliminary summary appeared in Proceedings of ACM Conference on Object-Oriented Programing, Systems, Languages, and Applications (OOPSLA), ACM SIGPLAN Notices, volume 34, number 10, pages 132-146, Denver, CO, October 1999.
Several recent studies have introduced lightweight versions of Java: reduced languages in which complex features like threads and reflection are dropped to enable rigorous arguments about key properties such as type safety. We carry this process a step further, omitting almost all features of the full language (including interfaces and even assignment) to obtain a small calculus, Featherweight Java, for which rigorous proofs are not only possible but easy. Featherweight Java bears a similar relation to Java as the lambda-calculus does to languages such as ML and Haskell. It offers a similar computational "feel," providing classes, methods, fields, inheritance, and dynamic typecasts, with a semantics closely following Java's. A proof of type safety for Featherweight Java thus illustrates many of the interesting features of a safety proof for the full language, while remaining pleasingly compact. The minimal syntax, typing rules, and operational semantics of Featherweight Java make it a handy tool for studying the consequences of extensions and variations. As an illustration of its utility in this regard, we extend Featherweight Java with generic classes in the style of GJ (Bracha, Odersky, Stoutamire, and Wadler) and give a detailed proof of type safety. The extended system formalizes for the first time some of the key features of GJ.
C<:D” at the end should be “
Cis not a subtype of
D). (The preprint available adove does not contain this error.)
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