A behavioral interface specification language that can be used to specify the behavior of Java modules.

Java extensions for high-level Web service development; Java-based high-level language to develop interactive Web services; merges main features of <bigwig> language into Java by providing explicit support for Web service sessions, safe ...

Java with support for generic programming in the form of parameterized types. Provides constrained parametric polymorphism, with advantages over some other proposals for adding genericity to Java. [Open Source, GPL]

Supports Design By Contract in Java. Discovers "contracts" during class loading and instruments the class bytecodes on-the-fly to check run-time contract violations. [Apache Open Source Licence]

A variant of Java that adds parametric polymorphism, first-class functions, and class cases and pattern matching to the language. The compiler compiles into Java byte code so the binaries can be run on a normal JVM. [Freeware]

Technical paper reviewing PolyJ, an extension to Java allowing parameterized types.

Modification of the Java language designed to have true support for the IEEE 754 floating point standard.

A framework for load-time transformation of Java programs. [Open Source, LGPL]

Supports load-time and runtime behavioural reflection in Java by allowing classes to be modified by Java code as they are loaded in. [Freeware, source available]

Support for generics. Superset of the Java programming language. Compatible with existing libraries. [Freeware]