MAKING THE FUTURE SAFE FOR THE PAST - ADDING GENERICITY TO THE JAVA(TM) PROGRAMMING LANGUAGE

We present GJ, a design that extends the Java programming language wit h generic types and methods. These are both explained and implemented by translation into the unextended language. The translation closely m imics the way generics are emulated by programmers: it erases all type parameters, maps type variables to their bounds, and inserts casts wh ere needed. Some subtleties of the translation are caused by the handl ing of overriding. GJ increases expressiveness and safety: code utiliz ing generic libraries is no longer buried under a plethora of casts, a nd the corresponding casts inserted by the translation are guaranteed to not fail. GJ is designed to be fully backwards compatible with the current Java language, which simplifies the transition from non-generi c to generic programming. In particular, one can retrofit existing lib rary classes with generic interfaces without changing their code. An i mplementation of GJ has been written in GJ, and is freely available on the web.