Focus Navigation

    TreeNode root = new DefaultMutableTreeNode("Root node");
    TreeModel model = new DefaultTreeModel(root);

Here’s another example with a real hierarchy. The root node contains two nodes, Node 1 and Group. The Group node contains Node 2 and Node 3 as subnodes.

    MutableTreeNode root = new DefaultMutableTreeNode("Root node");
    MutableTreeNode group = new DefaultMutableTreeNode("Group");
    root.insert(group, 0);
    root.insert(new DefaultMutableTreeNode("Node 1"), 1);
    group.insert(new DefaultMutableTreeNode("Node 2"), 0);
    group.insert(new DefaultMutableTreeNode("Node 3"), 1);

    TreeModel model = new DefaultTreeModel(root);

    JTree tree = new JTree(model);

    TreeExpansionListener
    TreeWillExpandListener
    TreeSelectionListener

    tree.addTreeSelectionListener(new TreeSelectionListener() {
      public void valueChanged(TreeSelectionEvent e) {
        TreePath tp = e.getNewLeadSelectionPath();
        System.out.println(tp.getLastPathComponent());
      }
    });

    //file: PartsTree.java
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    import javax.swing.event.*;
    import javax.swing.tree.*;

    public class PartsTree {
      public static void main(String[] args) {
        // create a hierarchy of nodes
        MutableTreeNode root = new DefaultMutableTreeNode("Parts");
        MutableTreeNode beams = new DefaultMutableTreeNode("Beams");
        MutableTreeNode gears = new DefaultMutableTreeNode("Gears");
        root.insert(beams, 0);
        root.insert(gears, 1);
        beams.insert(new DefaultMutableTreeNode("1x4 black"), 0);
        beams.insert(new DefaultMutableTreeNode("1x6 black"), 1);
        beams.insert(new DefaultMutableTreeNode("1x8 black"), 2);
        beams.insert(new DefaultMutableTreeNode("1x12 black"), 3);
        gears.insert(new DefaultMutableTreeNode("8t"), 0);
        gears.insert(new DefaultMutableTreeNode("24t"), 1);
        gears.insert(new DefaultMutableTreeNode("40t"), 2);
        gears.insert(new DefaultMutableTreeNode("worm"), 3);
        gears.insert(new DefaultMutableTreeNode("crown"), 4);

        // create the JTree
        final DefaultTreeModel model = new DefaultTreeModel(root);
        final JTree tree = new JTree(model);

        // create a text field and button to modify the data model
        final JTextField nameField = new JTextField("16t");
        final JButton button = new JButton("Add a part");
        button.setEnabled(false);
        button.addActionListener(new ActionListener() {
          public void actionPerformed(ActionEvent e) {
            TreePath tp = tree.getSelectionPath();
            MutableTreeNode insertNode =
                (MutableTreeNode)tp.getLastPathComponent();
            int insertIndex = 0;
            if (insertNode.getParent() != null) {
              MutableTreeNode parent =
                  (MutableTreeNode)insertNode.getParent();
              insertIndex = parent.getIndex(insertNode) + 1;
              insertNode = parent;
            }
            MutableTreeNode node =
                new DefaultMutableTreeNode(nameField.getText());
            model.insertNodeInto(node, insertNode, insertIndex);
          }
        });
        JPanel addPanel = new JPanel(new GridLayout(2, 1));
        addPanel.add(nameField);
        addPanel.add(button);

        // listen for selections
        tree.addTreeSelectionListener(new TreeSelectionListener() {
          public void valueChanged(TreeSelectionEvent e) {
            TreePath tp = e.getNewLeadSelectionPath();
            button.setEnabled(tp != null);
          }
        });

        // create a JFrame to hold the tree
        JFrame frame = new JFrame("PartsTree v1.0");

        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.setSize(200, 200);
        frame.add(new JScrollPane(tree));
        frame.add(addPanel, BorderLayout.SOUTH);
        frame.setVisible(true);
      }
    }

The example begins by creating a node hierarchy. The root node is called Parts. It contains two subnodes named Beams and Gears, as shown:

    MutableTreeNode root = new DefaultMutableTreeNode("Parts");
    MutableTreeNode beams = new DefaultMutableTreeNode("Beams");
    MutableTreeNode gears = new DefaultMutableTreeNode("Gears");
    root.insert(beams, 0);
    root.insert(gears, 1);

The Beams and Gears nodes contain a handful of items each.

The “Add a part” button inserts a new item into the tree at the level of the current node, and just after it. You can specify the name of the new node by typing it in the text field above the button. To determine where the node should be added, the current selection is first obtained in the anonymous inner class ActionListener:

    TreePath tp = tree.getSelectionPath();
    MutableTreeNode insertNode =
      (MutableTreeNode)tp.getLastPathComponent();

The new node should be added to the parent node of the current node, so it ends up being a sibling of the current node. The only hitch here is that if the current node is the root node, it won’t have a parent. If a parent does exist, we determine the index of the currently selected node, and then add the new node at the next index:

    int insertIndex = 0;
    if (insertNode.getParent() != null) {
      MutableTreeNode parent =
          (MutableTreeNode)insertNode.getParent();
      insertIndex = parent.getIndex(insertNode) + 1;
      insertNode = parent;
    }
    MutableTreeNode node =
        new DefaultMutableTreeNode(nameField.getText());
    model.insertNodeInto(node, insertNode, insertIndex);

You must add the new node to the tree’s data model using insertNodeInto()—not to the MutableTableNode itself. The model notifies the JTree that it needs to update itself.

We have another event handler in this example, one that listens for tree selection events. Basically, we want to enable our “Add a part” button only if a current selection exists:

    tree.addTreeSelectionListener(new TreeSelectionListener() {
      public void valueChanged(TreeSelectionEvent e) {
        TreePath tp = e.getNewLeadSelectionPath();
        button.setEnabled(tp != null);
      }
    });