JUNG

- JUNG — the Java Universal Network/Graph Framework--is a software library that provides a common and extendible language for the modeling, analysis, and visualization of data that can be represented as a graph or network. The JUNG architecture is designed to support a variety of representations of entities and their relations, such as directed and undirected graphs, multi-modal graphs, graphs with parallel edges, and hypergraphs. It provides a mechanism for annotating graphs, entities, and relations with metadata. The current distribution of JUNG includes implementations of a number of algorithms from graph theory, data mining, and social network analysis, such as routines for clustering, decomposition, optimization, random graph generation, statistical analysis, and calculation of network distances, flows, and importance measures (centrality, PageRank, HITS, etc.). Comprehensive, everything but the kitchen sink!

In order to run a JUNG-based application, you will need all the packages listed on the JUNG download page. (As of this writing, this includes .jar files for JUNG, version 1.3 (or later) of a Java runtime environment (JRE), Apache Jakarta commons-collections, the CERN Colt scientific library, and Xerces.

Building JUNG-based applications will require all of the above, plus the Java SDK (version 1.3 or later).

jung

Check here for more open source graph network visual tools in Java ;-)
http://www.manageability.org/blog/stuff/open-source-graph-network-visualization-in-java/view