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Screenshot
Demonstration of the GNU Classpath Swing |
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| Developer(s) | GNU Project (formally held by FSF) |
| Stable release | 0.98 [1] / February 5, 2009 |
| Development status | Active |
| Written in | C and Java |
| Operating system | Cross-platform |
| Type | Library |
| License | GNU GPL+GNU linking exception |
| Website | http://www.classpath.org |
GNU Classpath is a project aiming to create a free software implementation of the standard class library for the Java programming language. Despite the massive size of the library to be created, the majority of the task is already done, including Swing, CORBA, and other major parts. The Classpath developers have implemented almost all of the classes from J2SE 1.4 and 5.0. Classpath can thus be used to run popular Java-based software such as Vuze and Eclipse.
GNU Classpath has been one of the high priority directions of the GNU Project. While the source code of the "official" implementation from Sun Microsystems was available, the license did not allow distribution of any alterations. This was a major obstacle for many innovative projects that could not progress without altering this code. The GNU Classpath development community includes institutions focused on research of Java virtual machines, as well as companies interested in providing alternative Java runtimes.
GNU Classpath is a part of the Free Software Foundation. It was originally developed in parallel with libgcj due to license incompatibilities, but later the two projects merged.
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GNU Classpath is licensed under the GNU General Public License with a linking exception. This is a free software license. All code is formally owned by the Free Software Foundation, and this owner is bound by its own contractual obligations to the developers.
GNU Classpath is used by many free Java runtimes (like Kaffe, SableVM, JamVM, CACAO, Jikes RVM, VMkit) because every full-featured Java virtual machine must provide an implementation of the standard class libraries.
Some other uses include:
GNU Classpath development started in 1998 with five developers. During the history, it merged several times with other projects having similar goals (Kaffe, libgcj). In the past, GNU Classpath supplied its own virtual machine (Japhar). As Classpath was becoming a base library, shared with a lot of different projects, this virtual machine received less and less attention and is now no longer supported.
After implementing the majority of the official Java 1.4 API, the work in the project became more bug oriented rather than API coverage oriented. On October 24, 2006, the implementation of the last missing 1.4 class, HTMLWriter, was committed. The development speed (computed mathematically as the average number of the new lines of code per day) reached its highest ever in 2006.
The name GNU Classpath was originally suggested by Bradley M. Kuhn to one of the first developers, Paul Fisher. At the time, there was great concern in the Free Java implementations community about enforcement of Sun's trademark on Java against free implementations. Kuhn suggested the name $CLASSPATH, which is the environment variable used by most Java systems to indicate where the Java libraries reside on the computer. Since $CLASSPATH often expanded to a path name that included the word java (such as /usr/lib/java), it was a way to evoke the name Java without actually saying it. Fisher and other developers didn't like the unsightly use of the $ and all capital letters and settled on Classpath.
The maintainer takes care of the legal side of the project, prepares the regular project releases and does some quality management. The maintainer also grants the CVS access permissions.
Unlike some projects, GNU Classpath has no formal hierarchy. The work is done by the most technically capable, and there is no strict work division either. All code changes are first posted to the discussion list as patches where they can be opposed if needed. The project typically receives between five and eight patches per day.
The GNU Classpath library code coverage progress can be tracked against J2SE 1.4[2] and Java SE 5.0.[3]
GNU Classpath contains classes from the official java API namespace. Where calls to the native code are necessary or highly desired, this is done from the small number of "VM" classes. The name of such class matches the name of the class, requiring native methods plus the additional VM prefix: VMObject, VMString and so on. VM classes, stored separately from the rest of code, are package private and final. The methods of these classes contain the keyword native, indicating the necessity of the supporting library. Such library is provided by the authors of the Java virtual machine. Hence GNU Classpath can be connected to nearly any Java virtual machine if the sources of such machine are available and can be modified.
Before version 0.95, each GNU Classpath release consisted of two separate release tarballs; one that represented the state of the main development branch and another that contained the contents of a more experimental branch, supporting the additions, such as generics, enumerations and annotations, present in Java 1.5.
Since version 0.95, Java 1.5 additions like generics have been fully integrated into the main branch. The branch allows GCJ to use Eclipse compiler, ecj, to compile Java 1.5 source code to bytecode, which is then changed into native code by GCJ itself.[1]
Since version 0.95, GNU Classpath supports compiling and running the GPL open-source javac compiler using the Classpath run-time system (GIJ) and compiler (GCJ) and also allows to compile the GNU Classpath class library, tools and examples with javac itself.
GNU Classpath does not accept any code that has a non-free license, or that was automatically generated from code with a non-free license. The standard Java API contains numerous classes from the omg.org domain that are normally generated from the IDL files, released by the Object Management Group. The "use, but no modify" license of these files counts as non-free. Because of this reason, the mentioned classes in the GNU Classpath project were written by hand, using only the official printed OMG specifications. Hence this part of GNU Classpath is as free as any other code in the project.
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