A Design for Type-Directed Programming in Java

In this paper, we describe the design of several expressive new mechanisms for type-directed programming in Java, and show that these mechanisms are sound when included in a language similar to Featherweight Java. Basically, these new mechanisms pattern-match the name and structure of the type parameters of generic code, instead of the run-time classes of objects. Therefore, they naturally integrate with generics and provide strong guarantees about program correctness. As these mechanisms are based on pattern matching, they naturally and succinctly express many operations that depend on type information. Finally, they provide programmers with some degree of protection for their abstractions. Whereas instanceof and reflection can determine the exact run-time type of an object, our mechanisms allow any supertype to be supplied for analysis, hiding its precise structure.