The MIT Java Wordnet Interface (JWI) is a Java library for interfacing with the Wordnet electronic dictionary.
Taken from http://projects.csail.mit.edu/jwi/api/index.html
"It features API calls to retrieve index entries, synsets, morphological exceptions, and sense index entries from the Wordnet data files. It also has calls that allow browsing by following lexical and semantic pointers, and contains classes that can perform simple morphological processing. The library includes no GUI elements.
JWI is compatible with Wordnet versions 1.6 through 3.0, as well as a few other Wordnet variations. It is not compatible with Wordnet 1.5. JWI does not include the Wordnet dictionary itself: that must be downloaded separately from the Wordnet site at http://wordnet.princeton.edu."