title: How to implement a cluster graph in java
body: <p>I want to draw a cluster graph like <a href="http://www.langlor.com/index.php?/experiment/facebook-network-cluster/" rel="nofollow">this</a>. Is there a library for this? How should I  build the data structure to contain the input data? Like a dictionary with key as the node itself and value as an array with the nodes connecting to. What could be a more precise term to describe this?</p>