Proceedings of the 13th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications
Machine-Checking the Java Specification: Proving Type-Safety
Formal Syntax and Semantics of Java
Computer Languages, Systems and Structures
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We propose to extend the Java type system with a new construction: compound types, compositions of a class and any number of interfaces. Java users will benefit from the type system''s increased expressiveness, resulting in more kinds of errors being statically excludable. Compound types are particularly beneficial when several independently predefined standards need to be considered, as typically required by component software. Compound types are a strict extension of Java, i.e., existing programs need not to be modified. Our proposal can be implemented using the existing Java Virtual Machine. Our scientific contribution is a new combination of name and structural type equivcalence, which our Java extension exemplifies. Type matching is decided by structural comparison of compositions of named types; the latter being only compatible if explicitly declared so. This concept is applicable to several other languages than Java, as well. We support the feasibility of our proposal by a formal and mechanically verified proof of the extended type system''s soundness.