Getting the Most Recent Version
The newest version of J/Link can always be obtained from http://www.wolfram.com/solutions/mathlink/jlink. This User Guide describes version 2.1, an update that was released in May 2003. This is the version that is preinstalled in Mathematica 5.0. All users should upgrade to this version. Information on how to check your J/Link version can be found in Section 1.1.9.