Question

I have a class which extends JPanel, inside this panel i have added a lot of textField.
I want to add DocumentListener to every textField to detect changes to the text and change the bachground of txtField to red.
I did something as below but not yet working.

Can anyone help to solve it or any new suggestion is welcome?

public class MainDetailPanel extends JPanel implements DocumentListener{
public JLabel lblS_DWLDIRPRDPIC,lblL_DWLDIRPRD,lblS_UPLDIR,lblL_UPLDIR,lblS_DWLDIRPRD;
public JLabel lblFTP_DEFDIR,lblFTP_SERVER,lblFTP_POORT,lblFTP_USER,lblFTP_PASWOORD,lblL_CFDIR;
public JLabel lblL_DWLDIRPRDPIC,lblS_CFDIR,lblS_CFNAME,lblS_DWLNAMEPRD,lblS_DWLNAMEPRDPIC;

public JTextField txtL_DWLDIRPRD,txtS_DWLDIRPRDPIC,txtL_UPLDIR,txtS_DWLNAMEPRDPIC,txtL_CFDIR;
public JTextField txtFTP_DEFDIR,txtFTP_SERVER,txtFTP_POORT,txtFTP_USER,txtFTP_PASWOORD,txtS_UPLDIR;
public JTextField txtL_DWLDIRPRDPIC,txtS_CFDIR,txtS_CFNAME,txtS_DWLNAMEPRD,txtS_DWLDIRPRD;
public MainDetailPanel() {
    createComponents();
    layoutComponents();
}

private void createComponents() {
    txtL_DWLDIRPRD      = new JTextField(30);
    txtL_DWLDIRPRD.getDocument().addDocumentListener(this);
    txtS_DWLDIRPRDPIC   = new JTextField(30);
    txtL_UPLDIR         = new JTextField(30);
    txtS_DWLNAMEPRDPIC  = new JTextField(30);
    txtFTP_DEFDIR       = new JTextField(30);
    txtFTP_SERVER       = new JTextField(30);
    txtFTP_POORT        = new JTextField(30);
    txtFTP_USER         = new JTextField(30);
    txtFTP_PASWOORD     = new JTextField(30);
    txtL_CFDIR          = new JTextField(30);
    txtL_DWLDIRPRDPIC   = new JTextField(30);
    txtS_UPLDIR         = new JTextField(30);
    txtS_CFDIR          = new JTextField(30);
    txtS_CFNAME         = new JTextField(30);
    txtS_DWLNAMEPRD     = new JTextField(30);
    txtS_DWLDIRPRD      = new JTextField(30);

    lblFTP_DEFDIR       = new JLabel("FTP_DEFDIR");
    lblFTP_SERVER       = new JLabel("FTP_SERVER");
    lblFTP_POORT        = new JLabel("FTP_POORT");
    lblFTP_USER         = new JLabel("FTP_USER");
    lblFTP_PASWOORD     = new JLabel("FTP_PASWOORD");
    lblL_CFDIR          = new JLabel("L_CFDIR");
    lblL_UPLDIR         = new JLabel("L_UPLDIR");
    lblL_DWLDIRPRDPIC   = new JLabel("L_DWLDIRPRDPIC");
    lblS_CFDIR          = new JLabel("S_CFDIR");
    lblS_CFNAME         = new JLabel("S_CFNAME");
    lblS_DWLNAMEPRD     = new JLabel("S_DWLNAMEPRD");
    lblS_DWLDIRPRD      = new JLabel("S_DWLDIRPRD");
    lblS_DWLNAMEPRDPIC  = new JLabel("S_DWLNAMEPRDPIC");
    lblS_UPLDIR         = new JLabel("S_UPLDIR");
    lblS_DWLDIRPRDPIC   = new JLabel("lblS_DWLDIRPRDPIC");
    lblL_DWLDIRPRD      = new JLabel("lblL_DWLDIRPRD");
}

private void layoutComponents() {
    setLayout(new ParagraphLayout());
    add(lblFTP_DEFDIR, ParagraphLayout.NEW_PARAGRAPH);
    add(txtFTP_DEFDIR);
    add(lblFTP_SERVER, ParagraphLayout.NEW_PARAGRAPH);
    add(txtFTP_SERVER);
    add(lblFTP_POORT, ParagraphLayout.NEW_PARAGRAPH);
    add(txtFTP_POORT);
    add(lblFTP_USER, ParagraphLayout.NEW_PARAGRAPH);
    add(txtFTP_USER);
    add(lblFTP_PASWOORD, ParagraphLayout.NEW_PARAGRAPH);
    add(txtFTP_PASWOORD);
    add(lblL_CFDIR, ParagraphLayout.NEW_PARAGRAPH);
    add(txtL_CFDIR);
    add(lblL_UPLDIR, ParagraphLayout.NEW_PARAGRAPH);
    add(txtL_UPLDIR);
    add(lblL_DWLDIRPRD, ParagraphLayout.NEW_PARAGRAPH);
    add(txtL_DWLDIRPRD);
    add(lblL_DWLDIRPRDPIC, ParagraphLayout.NEW_PARAGRAPH);
    add(txtL_DWLDIRPRDPIC);
    add(lblS_UPLDIR, ParagraphLayout.NEW_PARAGRAPH);
    add(txtS_UPLDIR);
    add(lblS_CFDIR, ParagraphLayout.NEW_PARAGRAPH);
    add(txtS_CFDIR);
    add(lblS_CFNAME, ParagraphLayout.NEW_PARAGRAPH);
    add(txtS_CFNAME);
    add(lblS_DWLNAMEPRD, ParagraphLayout.NEW_PARAGRAPH);
    add(txtS_DWLNAMEPRD);
    add(lblS_DWLDIRPRD, ParagraphLayout.NEW_PARAGRAPH);
    add(txtS_DWLDIRPRD);
    add(lblS_DWLNAMEPRDPIC, ParagraphLayout.NEW_PARAGRAPH);
    add(txtS_DWLNAMEPRDPIC);
    add(lblS_DWLDIRPRDPIC, ParagraphLayout.NEW_PARAGRAPH);
    add(txtS_DWLDIRPRDPIC);
}

public void insertUpdate(DocumentEvent e) {
    ((JTextField)e.getDocument()).setBackground(Color.red);
}

public void removeUpdate(DocumentEvent e) {
    ((JTextField)e.getDocument()).setBackground(Color.red);
}

public void changedUpdate(DocumentEvent e) {
    ((JTextField)e.getDocument()).setBackground(Color.red);
}


}

Answer 1

You can’t cast the Document to a JTextField. JTextField has a document. But JTextField is not a Document.

AFAIK, you’ll have to use a separate listener for every JTextField, and give the reference of the JTextField to your listener:

private static class BecomingRedDocumentListener implements DocumentListener {
    private JTextField textField;

    public BecomingRedDocumentListener(JTextField textField) {
        this.textField = textField;
    }
    @Override
    public void insertUpdate(DocumentEvent e) {
        textField.setBackground(Color.red);
    }
    @Override
    public void removeUpdate(DocumentEvent e) {
        textField.setBackground(Color.red);
    }
    @Override
    public void changedUpdate(DocumentEvent e) {
        textField.setBackground(Color.red);
    }
}

And you should use a factory method to create your textfields:

private JTextField createTextFieldBecomingRed() {
    JTextField tf = new JTextField(30);
    tf.addDocumentListener(new BecomingRedDocumentListener(tf));
    return tf;
}