java-aggiunta cartelle JTree

[tony1]

Sto realizzando per esercizio un sorgente dove inserendo in una text il nome di una cartella premendo un button dovrei aggiungere questa cartella al JTree.Questo è il codice:

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


public class TreeDemo1 extends JFrame implements ActionListener{
    
    
    
    private JTree tree;
    JTextField c=new JTextField(15);
    JButton d=new JButton("Aggiungi");
    JLabel x=new JLabel();
    
    DefaultMutableTreeNode top =new DefaultMutableTreeNode("The Java Series");
    DefaultMutableTreeNode category = null;
    

public TreeDemo1() {
    super.setSize(300,300);
    
    
    createNodes(top);
    
    tree = new JTree(top);
    
    JScrollPane treeView = new JScrollPane(tree);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel pannello=new JPanel();
        tree.setBounds(12, 12, 373, 347);
        pannello.add(tree);
        pannello.add(c);
        pannello.add(d);
        pannello.add(x);
        setContentPane(pannello);
        d.addActionListener(this);
            
    }

private void createNodes(DefaultMutableTreeNode top) {
    
    DefaultMutableTreeNode book = null;
    
     
    category = new DefaultMutableTreeNode("Books for Java Programmers");
    top.add(category);
    
    //original Tutorial
    //book = new DefaultMutableTreeNode("The Java Tutorial: A Short Course on the Basics");
    //category.add(book);
    
    //Tutorial Continued
    book = new DefaultMutableTreeNode("The Java Tutorial Continued: The Rest of the JDK");
    category.add(book);
    
    //Swing Tutorial
    book = new DefaultMutableTreeNode("The Swing Tutorial: A Guide to Constructing GUIs");
    category.add(book);

    //...add more books for programmers...

    category = new DefaultMutableTreeNode("Books for Java Implementers");
    top.add(category);

    //VM
    book = new DefaultMutableTreeNode("The Java Virtual Machine Specification");
    category.add(book);

    //Language Spec
    book = new DefaultMutableTreeNode("The Java Language Specification");
    category.add(book);
                     
    
}
private void creaNodi() {
   
   DefaultMutableTreeNode category = null;
      category=new DefaultMutableTreeNode(c.getText());
        top.add(category);
        x.setText(category.toString());
    }

public static void main(String[] args){
    TreeDemo1 a=new TreeDemo1();
    a.setVisible(true);
}

public void actionPerformed(ActionEvent e) {
    creaNodi();
    //x.setText(c.getText());
}
}

Il problema però che nella funzione creaNodi non mi viene aggiunta nessuna cartella.Non capisco il perchè.Grazie mille.