how do I get the current node selection in a Jtree?

Hi,

I have been trying to figure out how to access the current node in a JTree. I have a main class where the tree is defined. When the add button is pressed, the add method from another class is to be invoked. But the listener is defined in the main class, how do I pass the variable to this other class?

class SelectableTree extends JPanel implements TreeSelectionListener
{  
   private JTree       tree;         // Reference tree that will be created.
   private JLabel      statusField;  // Reference label for messages.
   private JScrollPane scrollArea;   // Reference scroll area to display tree.
   private int         nodeNum = 1;  // Next available node number.

// The constructor method.
	public SelectableTree()
   {  
      // Declare references to tree nodes.
      DefaultMutableTreeNode grandChild, child;
      // create the root.
      DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");

// In a loop create 3 child nodes, each with 4 grandchildren nodes. 
      // Link the children to the root and the grandchildren to the children.
      for (int childNdx = 1; childNdx <= 4; childNdx++)
      {  
         child = new DefaultMutableTreeNode("Node " + nodeNum++);
         root.add(child);
         for (int grandNdx=1; grandNdx<=4; grandNdx++)
         {  
            grandChild = new DefaultMutableTreeNode("Node " + nodeNum++);
            child.add(grandChild);
         }
      }

// Instantiate the tree and add the selection listener.
	
		 
      DefaultTreeModel treeModel = new DefaultTreeModel(root);    // step 5 in instruction
      tree = new JTree(treeModel);
      tree.addTreeSelectionListener(this);
      tree.setEditable(true);
      for (int row = 0; row < tree.getRowCount(); row++) 
            tree.expandRow(row);

// create the two main GUI components
      scrollArea  = new JScrollPane(tree);
      statusField = new JLabel("Current Selection: NONE");

// Instantiate the Panels on the top and add the selection listener.		  
		
        JTabbedPane tp = new JTabbedPane();  
        tp.addTab ("Modify", new ModifyPanel(treeModel);
        tp.addTab ("Expand/Collapse Tree", new TreeDisplay());
        tp.addTab ("Expand/Collape Path", new PathDisplay());
        tp.setSelectedIndex(0);

// add the components
        setLayout(new BorderLayout());
        add(scrollArea, BorderLayout.CENTER);
        add(statusField, BorderLayout.SOUTH);
        add(tp, BorderLayout.NORTH);

} // constructor

// Method to respond to tree selection changes.
   public void valueChanged(TreeSelectionEvent event) 
   {  
      Object node = tree.getLastSelectedPathComponent();
      String name;
      name = (node == null) ? "NONE" : node.toString();

statusField.setText("Current Selection: " + name);

} // valueChanged method
}

public class ModifyPanel extends JPanel implements ActionListener
{
   // instance variables
   private JButton addButton;
   private JButton removeButton;
   private JButton changeButton;
   private int childNum=1;
   private JTree tree;

public ModifyPanel(DefaultTreeModel treeModel)
  {

tree = new JTree(treeModel);
	setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
	DefaultMutableTreeNode newNode;
	System.out.println(node.toString());
	
                 // create the Add button
                 addButton = new JButton("Add");
                 addButton.setToolTipText("Add a node");

// create the Remove button
                   removeButton = new JButton("Remove");
                   removeButton.setToolTipText("Remove a node");

// create the Change button
                   changeButton = new JButton("Change");
                   changeButton.setToolTipText("Change the value of Node");
		
		
                   // register my event handler with the buttons
                   addButton.addActionListener(this);
                   removeButton.addActionListener(this);
                   changeButton.addActionListener(this);

// add the buttons to the panel
                   add(addButton);
                   add(changeButton);
                   add(removeButton);
 
   }

// ActionListener event handler
   public void actionPerformed(ActionEvent e)
   {
      Object c = e.getSource();

if (c == addButton)
		{
			DefaultMutableTreeNode newNode;
			DefaultMutableTreeNode node = null;
			DefaultMutableTreeNode node = (DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
						
			newNode = new DefaultMutableTreeNode("Node" + childNum++);
			if (node != null)
				System.out.println(node.toString());
			else
				System.out.println("Empty node:" + node);

System.out.println(newNode);
			//treeModel.insertNodeInto(newNode,node, node.getChildCount(node,1));
			//treeModel.scrollPathtoVisible(new TreePath(newNode.getPath()));
			
      }
		
		
      else if (c == removeButton) 
      {
	.....
      }
		else 
		{
                                   ............
		}

} // method actionPerformed
	
	
}

At this point, I am just trying to see the node content. This piece of code, gives null all the time. I cannot proceed to add till I can identify the node where I have to insert.

Please help.
Thanks,
Juliana

Does this:

#
# DefaultMutableTreeNode node = null;
# DefaultMutableTreeNode node = (DefaultMutableTreeNode)tree.getLastSelectedPathComponent();

compile?

Hello Albareto,
Well actually, I have been modifying and test the code so much, I think I put an older version here. The 2nd statement should be just
Regards,
Juliana

I don't really understand the flow of your application, who calls to actionPerformed? What's the value of the tree at that point? What's doing tree.getLastSelectedPathComponent and why is it returning null?

There's a good little tutorial about how to use the JTree component over at Sun.
It covers node selection and retrieval of data from tree nodes. Have a look.