Java Swing: JTree DefaultMutableTreeNode not updating

Question

I have recently been working on a Java Swing project and today I get stuck when modifying childrens of a DefaultMutableTreeNode.

The following SSCCE illustrates the problem:

import java.awt.event.*;
import javax.swing.*;
import javax.swing.tree.*;

public class Test
{
    private static boolean executed = false;
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                //
                final DefaultMutableTreeNode root = new DefaultMutableTreeNode("root");
                final JTree tree = new JTree(root);
                tree.addMouseListener(new MouseAdapter()
                {
                    @Override
                    public void mousePressed(MouseEvent ev)
                    {
                        if (ev.getClickCount() == 2)
                        {
                            root.removeAllChildren();
                            for (String s: get())
                            {
                                root.add(new DefaultMutableTreeNode(s));
                                System.out.println(s + " added");
                            }
                            System.out.println();
                            tree.expandPath(tree.getSelectionPath());
                        }
                    }
                });
                frame.add(tree);
                frame.setSize(200,200);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    static String[] get()
    {
        if (!executed)
        {
            executed = true;
            return new String[]{"a","b","c"};
        }
        else return new String[]{"a","b","c","d"};
    }
}

As you see, the first time the get() method is invoked it returns a 3-element array, and a 4-element one afterwards. When I double-click (actually press) the root node for the first time there should be three children nodes (a, b and c), and the program behaves as expected. When I double-click the root node again I suppose it would have four children nodes. However it doesn't. When you double-click for the second time there are still only three, not four children nodes.

Did I make a mistake? Thanks for help in advance.

Answer 1

you should notify the model about changes use reload() method

add this lines before expand path like bellow

 DefaultTreeModel model = (DefaultTreeModel) tree.getModel();
 model.reload(root); // notify changes to model 
 tree.expandPath(tree.getSelectionPath());