Implementing dynamic language features in Java using dynamic code generation

Compared to dynamic object-oriented languages like CommonLisp or Smalltalk, Java has a fairly simple and restrictive object and type system. Some of the key differences between Java and these other languages are that they offer structural conformance, automatic delegation and dynamic mix-ins. When such constructs are needed in a language like Java, they are usually expressed in terms of standard object-oriented design patterns, requiring the manual implementation of “glue” or “helper” classes. This paper describes ways in which such features can be provided efficiently and automatically in terms of Java´s platform-independent binary format and dynamic loading mechanisms. The implementation does not require any changes to the Java runtime environment, byte-codes or class loader, and it yields a performance that is comparable to manually implemented design patterns. The approach should prove useful both as a programming tool for Java and as a strategy for building efficient implementations of dynamic languages on top of the Java Virtual Machine