Java has multiple inheritance of interfaces, but only single inheritance of code via classes. This situation results in duplicated code in Java library classes and application code. We describe a generalization to the Java language syntax and the Java Virtual Machine (JVM) to support multiple inheritance of code. Our approach places multiply inherited code in a new language construct called an implementation, which lies between an interface and a class in the inheritance hierarchy. This extension is implemented by making minimal changes to the Java syntax, small changes to a compiler (IBM Jikes), and modest localized changes to a JVM (SUN JDK 1.2.2).
