Retrotranslator is a tool that makes Java applications compatible with Java 1.4, Java 1.3 and other environments. It supports all Java 5.0 language features and a significant part of the Java 5.0 API on both J2SE 1.4 and J2SE 1.3. In other Java environments only the Java 5.0 features that don't depend on the new API are supported. Retrotranslator employs the ASM bytecode manipulation framework to transform compiled Java classes and the backport of the Java 5.0 concurrency utilities to emulate the Java 5.0 API.