Java Tutorial/Swing Event/TreeModelListener

How to Write a TreeModel Listener

Detect when the data displayed by a tree changes.

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.event.TreeModelEvent;
import javax.swing.event.TreeModelListener;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
class MyTreeModelListener implements TreeModelListener {
  public void treeNodesChanged(TreeModelEvent e) {
    DefaultMutableTreeNode node;
    node = (DefaultMutableTreeNode) (e.getTreePath().getLastPathComponent());
    try {
      int index = e.getChildIndices()[0];
      node = (DefaultMutableTreeNode) (node.getChildAt(index));
    } catch (NullPointerException exc) {
    }
    System.out.println("The user has finished editing the node.");
    System.out.println("New value: " + node.getUserObject());
  }
  public void treeNodesInserted(TreeModelEvent e) {
    System.out.println(e);
  }
  public void treeNodesRemoved(TreeModelEvent e) {
    System.out.println(e);
  }
  public void treeStructureChanged(TreeModelEvent e) {
    System.out.println(e);
  }
}
public class TreeExpansionListenerDemo {
  public static void main(String args[]) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
    JTree tree = new JTree(root);
    DefaultTreeModel treeModel = new DefaultTreeModel(root);
    treeModel.addTreeModelListener(new MyTreeModelListener());
    treeModel.insertNodeInto(new DefaultMutableTreeNode("A") ,root,0);
    root.add(new DefaultMutableTreeNode("B"));
    root.add(new DefaultMutableTreeNode("C"));
    
    JScrollPane scrollPane = new JScrollPane(tree);
    frame.add(scrollPane, BorderLayout.CENTER);
    frame.setSize(300, 150);
    frame.setVisible(true);
  }
}