A lot depends on the level at which you plan to address this problem. Larger libraries are more powerful, but they typically have a steeper learning curve. Here are some approaches to consider:
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JHotDraw
, cited here, is a meta-library for creating custom graph editors. -
Prefuse
, demonstrated here, supports graph modeling, visualization, and interaction. -
GraphViz
, examined here, is a graph visualization library developed by AT&T. -
JGraph
, linked here, is a popular graph visualization library. -
GraphPanel
, illustrated here, shows a very basic graph editing panel.