JRuby

JRuby is a Java implementation of the Ruby interpreter, being developed by the JRuby team.
JRuby is free software released under a three-way CPL/GPL/LGPL license.
JRuby is tightly integrated with Java to allow the embedding of the interpreter into any Java application with full two-way access between the Java and the Ruby code (compare Jython for the Python language).
JRuby's lead developers are Charles Nutter , Thomas Enebo, Ola Bini,] and Nick Sieger. In September 2006, Sun Microsystems hired Enebo and Nutter to work on JRuby full time. In June 2007, ThoughtWorks hired Ola Bini to work on Ruby and JRuby.

History

JRuby was originally created by Jan Arne Petersen, in 2001. At that time and for several years following, the code was a direct port of the Ruby 1.6 C code. With the release of Ruby 1.8.6, an effort began to update JRuby to 1.8.6 features and semantics. Since 2001, several contributors have assisted the project, leading to the current (2008) core team of four members.
The Netbeans Ruby Pack, available since NetBeans 6.0, allows IDE development with Ruby and JRuby, as well as Ruby on Rails for the two implementations of Ruby .
JRuby 1.1 added Just-in-time compilation and Ahead-of-time compilation modes to JRuby and is faster in most cases than the current Ruby 1.8.7 reference implementation].
JRuby 1.1.1 is stated to be packaged in Fedora 9].
Since version 1.1.1, the JRuby team began to issue point releases often to quickly address issues that are brought up by users[7].
JRuby support Ruby MRI 1.8.6, and work is ongoing to add a Ruby 1.9 support, but as Ruby 1.8.7 is mainly a transitional version to 1.9, it will not be supported.

Design

Since early 2006, the current JRuby core team has endeavored to move JRuby beyond being a simple C port, to support better performance and to aid eventual compilation to Java bytecode. To support this end, the team set an ambitious goal: to be able to run Ruby on Rails unmodified using JRuby. In the process of achieving this goal, the JRuby test suite expanded to such extent that the team gained confidence in the "correctness" of JRuby. As a result, toward the end of 2006 and in the beginning of 2007, they began to commit much more complicated redesigns and refactorings of JRuby's core subsystems.
JRuby is designed to work as a mixed-mode virtual machine for Ruby, where code can be either interpreted directly, just-in-time compiled at runtime to Java bytecode, or ahead-of-time compiled to Java bytecode before execution. Until October 2007, only the interpreted mode supported all Ruby's constructs, but a full AOT/JIT compiler is available since version 1.1[19]. The compiler design allows for interpreted and compiled code to run side-by-side, as well as decompilation to reoptimize and outputting generated bytecode as Java class files.

(Taken from http://en.wikipedia.org/wiki/Jruby on December 31, 2008)