Problem with new window opening with basic test JTree program

Question

I'm still getting to grips with Swing, and have now moved on to basic JTrees.
I'm currently trying to use an add and delete button to add new nodes to the root etc. The addition and deletion is working ok, except that each time the addButton is pressed, a completely new window is created on top of the current window with the new node added to the root etc.
I know this is probably a simple mistake, but I can't quite see it at the moment.
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 TreeAdditionDeletionTester_1 extends JFrame implements ActionListener
    private JTree tree;
    private DefaultTreeModel treeModel;
    private DefaultMutableTreeNode rootNode;
    private JButton addButton;
    private JButton deleteButton;
    private JPanel panel;
    private int newNodeSuffix = 1;
    private static String Add_Command = "Add Node";
    private static String Delete_Command = "Remove Node";
    //DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Root");
    //TreeAdditionDeletionTester_1 treeChange;
    public TreeAdditionDeletionTester_1() 
        setTitle("Tree with Add and Remove Buttons");
        //DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Root");
        rootNode = new DefaultMutableTreeNode("Root");
        treeModel = new DefaultTreeModel(rootNode);
        tree = new JTree(treeModel);
        tree.setEditable(false);
        tree.setSelectionRow(0);
        JScrollPane scrollPane = new JScrollPane(tree);
        getContentPane().add(scrollPane, BorderLayout.CENTER);
        JPanel panel = new JPanel();
        addButton = new JButton("Add Node");
        addButton.setActionCommand(Add_Command);
        addButton.addActionListener(this);
        panel.add(addButton);
        getContentPane().add(panel, BorderLayout.SOUTH);
        deleteButton = new JButton("Delete Node");
        deleteButton.setActionCommand(Delete_Command);
        deleteButton.addActionListener(this);
        panel.add(deleteButton);
        getContentPane().add(panel, BorderLayout.SOUTH);    
        setSize(300, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
    public void actionPerformed(ActionEvent event) 
       TreeAdditionDeletionTester_1 treeChange = new TreeAdditionDeletionTester_1();
        String command = event.getActionCommand();
        if (Add_Command.equals(command)) {
            //Add button clicked
            treeChange.addObject("New Node " + newNodeSuffix++);
        } if (Delete_Command.equals(command)) {
            //Remove button clicked
            treeChange.removeCurrentNode();
    public void removeSelectedNode()
        //get the selected node
        DefaultMutableTreeNode selNode = (DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
        //method from Class JTree
        if (selNode != null)
            //get the parent of the selected node
            MutableTreeNode parent = (MutableTreeNode)(selNode.getParent());
            //getParent() from Interface TreeNode
            // if the parent is not null
            if (parent != null)
                //remove the node from the parent
                treeModel.removeNodeFromParent(selNode);//method from Class DefaultTreeModel
                return;
    public DefaultMutableTreeNode addObject(Object child) {
        DefaultMutableTreeNode parentNode = null;
        TreePath parentPath = tree.getSelectionPath();
        if (parentPath == null) {
            parentNode = rootNode;
        } else {
            parentNode = (DefaultMutableTreeNode)
                         (parentPath.getLastPathComponent());
        return addObject(parentNode, child, true);
    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
                                            Object child,
                                            boolean shouldBeVisible) {
        DefaultMutableTreeNode childNode =
                new DefaultMutableTreeNode(child);
        if (parent == null) {
            parent = rootNode;
        treeModel.insertNodeInto(childNode, parent,
                                 parent.getChildCount());
        //Make sure the user can see the new node.
        if (shouldBeVisible) {
            tree.scrollPathToVisible(new TreePath(childNode.getPath()));
        return childNode;
    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
                                            Object child) {
        return addObject(parent, child, false);
    public void removeCurrentNode() {
        TreePath currentSelection = tree.getSelectionPath();
        if (currentSelection != null) {
            DefaultMutableTreeNode currentNode = (DefaultMutableTreeNode)
                         (currentSelection.getLastPathComponent());
            MutableTreeNode parent = (MutableTreeNode)(currentNode.getParent());
            if (parent != null) {
                treeModel.removeNodeFromParent(currentNode);
                return;
     * Main method to run as an Application
    public static void main(String[] arg) 
        TreeAdditionDeletionTester_1 addDeleteTree = new TreeAdditionDeletionTester_1();
}      Thanks.

Answer 1

I'm currently trying to use an add and delete button
to add new nodes to the root etc. The addition and
deletion is working ok, except that each time the
addButton is pressed, a completely new window is
created on top of the current window with the new
node added to the root etc.
I know this is probably a simple mistake, but I can't
quite see it at the moment.
Look at the actionPerformed code for your buttons. The first thing you do there is to create a new TreeAdditionDeletionTester_1, so I don't know why you are surprised you get a new window. There is no need to create a new instance in there, just call addObject/removeCurrentNode on the "this" instance.