Free Java implementations

Free Java implementations are software projects that implement Oracle's Java technologies and are distributed under free software licences, making them free software. Sun released most of its Java source code as free software in May 2007, so it can now almost be considered a free Java implementation. Java implementations include compilers, runtimes, class libraries, etc. Advocates of free and open source software refer to free or open source Java virtual machine software as free runtimes or free Java runtimes. Some advocates in this movement prefer not to use the term "Java" as it has trademark issues associated with it. Hence, even though it is a "free Java movement", the term "free Java runtimes" is avoided by them. The first free project to offer substantial parts of Java platform functionality was likely guavac, which began some time before November 1995. Since then, the free software movement developed other Java compilers, most notably the GNU Compiler for Java. Others include the Eclipse Java Compiler (ECJ), which is maintained by the Eclipse Foundation, and Jikes, which is no longer actively maintained. Since the GNU Compiler Collection's 4.3 release, GCJ (its Java compiler) is using the ECJ parser front-end for parsing Java. Examples of free runtime environments include Kaffe, SableVM and gcj. GNU Classpath is the main free software class library for Java. Most free runtimes use GNU Classpath as their class library. In May 2005, Apache Harmony was announced, however, the project chose the Apache License, which was at the time incompatible with all existing free Java implementations. Another event in May 2005 was the announcement that OpenOffice.org 2.0 would depend on Java features which free software implementations couldn't provide. Following controversy, OpenOffice.org adopted a guideline requiring it to work with free Java implementations. Notable applications that already worked with free software Java implementations before November 2006 include OpenOffice.org and Vuze, both of which work when compiled with GCJ.