java - JTextField changed

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Java

this is my code

the build

UserNameTextBox = new JTextField();
        UserNameTextBox.setHorizontalAlignment(SwingConstants.CENTER);
        UserNameTextBox.setBounds(562, 326, 119, 20);
        contentPane.add(UserNameTextBox);
        UserNameTextBox.setColumns(10);

the code

	URL url2 = new URL("http://mcskinsearch.com/img/cache/pic/z3nox.png");
		image2 = new ImageIcon(ImageIO.read(url2));
		image2 = new ImageIcon(image2.getImage().getScaledInstance(297, 297, BufferedImage.SCALE_SMOOTH));
		FrontImage = new JLabel(image2);
		FrontImage.setHorizontalAlignment(SwingConstants.LEFT);
		FrontImage.setVerticalAlignment(SwingConstants.TOP);
		FrontImage.setBounds(10, 11, 151, 297);
		contentPane.add(FrontImage);

UserNameTextBox.getDocument().addDocumentListener(new DocumentListener() {
     public void removeUpdate(DocumentEvent e) {
        // TODO add code!

     }

     public void insertUpdate(DocumentEvent e) {
        // TODO add code!

     }

     public void changedUpdate(DocumentEvent e) {
        // TODO add code!
	URL url3 = new URL("http://mcskinsearch.com/img/cache/pic/z3nox.png");
		image3 = new ImageIcon(ImageIO.read(url3)); 
     }
  });

my error is located

public void changedUpdate(DocumentEvent e) {
    // TODO add code!
URL url3 = new URL("http://mcskinsearch.com/img/cache/pic/" + UserNameTextBox.text  +   ".png");
    image3 = new ImageIcon(ImageIO.read(url3));
 }

the problem is, I cannot acess and change the varible of the url so whenthe user types in like a name the url will change so then the image it is showing will change, cna some one please help, why wont it let me change it?