This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Check out TreeModelListener. Note that all changes to any nodes must go through the model. That means, for example, that when you modify a DefaultMutableTreeNode that's part of a DefaultTreeModel, you call nodeChanged on that model afterwards.