COMPATIBLE GENERICITY WITH RUN-TIME TYPES FOR THE JAVA(TM) PROGRAMMING LANGUAGE

The most serious impediment to writing substantial programs in the Jav a(TM) programming language is the lack of a genericity mechanism for a bstracting classes and methods with respect to type. During the past t wo years: several research groups have developed Java extensions that support various forms of genericity, but none has succeeded in accommo dating general type parameterization (akin to Java arrays) while retai ning compatibility with the existing Java Virtual Machine. In this pap er, we explain how to support general type parameterization-including both non-variant and covariant subtyping-on top of the existing Java V irtual Machine at the cost of a larger code footprint and the forwardi ng of some method calls involving parameterized classes and methods. O ur language extension is forward and backward compatible with the Java 1.2 language and run-time environment: programs in the extended langu age will run on existing Java 1.2 virtual machines (relying only on th e unparameterized Java core libraries) and all existing Java 1.2 progr ams have the same binary representation and semantics (behavior) in th e extended language.