Node labelling within a tree using depth-first traversal

[Adriana Woolley]

Hello,

I'm currently trying to work my way through Java and need some advice on using and traversing trees. I've written a basic JTree program, which allows the user to add and delete nodes. Each new node is labelled in a sequential order and not dependent upon where they are added to the tree.

Basically, what is the best way to add and delete these new nodes with labels that reflect their position in the tree in a depth-first traversal?

ie: the new node's label will correctly reflect its position in the tree and the other labels will change to reflect this addition of a new node.

I've searched Google and can't seem to find any appropriate examples for this case.

My current code is as follows,

import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*; 
import javax.swing.event.*;
import javax.swing.tree.*; 
 
public class BasicTreeAddDelete extends JFrame implements ActionListener 
{  
    private JTree tree; 
    private DefaultTreeModel treeModel; 
    private JButton addButton; 
    private JButton deleteButton;
    private int newNodeSuffix = 1;
   
    public BasicTreeAddDelete()  
    {  
        setTitle("Basic Tree with Add and Delete Buttons"); 
        
        DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Root"); 
        
        treeModel = new DefaultTreeModel(rootNode);
        
        tree = new JTree(treeModel); 
         
        JScrollPane scrollPane = new JScrollPane(tree); 
        getContentPane().add(scrollPane, BorderLayout.CENTER); 
         
        JPanel panel = new JPanel(); 
        addButton = new JButton("Add Node"); 
        addButton.addActionListener(this); 
        panel.add(addButton); 
        getContentPane().add(panel, BorderLayout.SOUTH); 
        deleteButton = new JButton("Delete Node"); 
        deleteButton.addActionListener(this); 
        panel.add(deleteButton); 
        getContentPane().add(panel, BorderLayout.SOUTH);     
        
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(400, 300); 
        setVisible(true); 
    } 
 
    public void actionPerformed(ActionEvent event)  
    { 
        DefaultMutableTreeNode selectedNode = (DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
        
        if(event.getSource().equals(addButton)) 
        { 
            if (selectedNode != null) 
            { 
                // add the new node as a child of a selected node at the end
                DefaultMutableTreeNode newNode = new DefaultMutableTreeNode("New Node" + newNodeSuffix++); 
                  treeModel.insertNodeInto(newNode, selectedNode, selectedNode.getChildCount()); 
                   
                  //make the node visible by scrolling to it
                TreeNode[] totalNodes = treeModel.getPathToRoot(newNode); 
                TreePath path = new TreePath(totalNodes); 
                tree.scrollPathToVisible(path);                
            } 
        }             
        else if(event.getSource().equals(deleteButton))
        {
            //remove the selected node, except the parent node
            removeSelectedNode();            
        }            
    } 
 
    public void removeSelectedNode() 
    {
        DefaultMutableTreeNode selectedNode = (DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
        
        if (selectedNode != null) 
        { 
            //get the parent of the selected node
            MutableTreeNode parent = (MutableTreeNode)(selectedNode.getParent());
        
            // if the parent is not null
            if (parent != null) 
            {
                //remove the node from the parent
                treeModel.removeNodeFromParent(selectedNode);
            }    
        } 
    }
 
    public static void main(String[] arg)  
    {  
        BasicTreeAddDelete basicTree = new BasicTreeAddDelete(); 
    } 
}      

Thank you for any help.