Featherweight Java (http://www.fos.kuis.kyoto-u.ac.jp/~igarashi/papers/fj.html) was a seminal paper which showed type soundness for Java. The formal syntax was a subset of Java subset and preserved the interesting features in the semantics (as opposed to encoding a language in an extension of the lambda calculus, which is an alternative style of formalisation). So, "featherweight flavour" refers to formal type systems work which follows this style of formalisation.

I'd expect something along the lines of:

> 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.

You can see a few of his pubs on his website: http://www.ncameron.org/papers/index.html