private JTree createSubjectExplorer() {
final JTree tree = new JTree(application.getSubjectHierarchy());
tree.setBorder(BorderFactory.createEmptyBorder());
tree.setRootVisible(false);
tree.setShowsRootHandles(true);
tree.setEditable(true);
tree.setCellRenderer(new SubjectExplorerRenderer());
tree.setCellEditor(new SubjectExplorerEditor(application, tree));
application.getSubjectHierarchy().addTreeModelListener(new TreeExpander());
// This line allows the cell renderer to provide a custom tooltip for each node.
ToolTipManager.sharedInstance().registerComponent(tree);
return tree;
}
