Transferring focus to the next input field

Question

I have a group of input fields which are supposed to accept a single digit as input. By using a custom document, I am able to restrict the input. Once a valid input character has been entered, I would like to automatically transfer focus to the next JTextField from within my Document's insertString() method. Is there any way I could do something like that?

Answer 1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class ValidTransit
    private JPanel getContent()
        FocusListener fl = new EntryListener();
        DocumentListener tl = new TransitChecker();
        DocumentFilter vf = new ValidFilter();
        JPanel panel = new JPanel();
        panel.add(getTextField(fl, tl, vf));
        panel.add(getTextField(fl, tl, vf));
        panel.add(getTextField(fl, tl, vf));
        return panel;
    private JTextField getTextField(FocusListener fl, DocumentListener dl,
                                    DocumentFilter vf)
        JTextField tf = new JTextField(2);
        tf.addFocusListener(fl);
        AbstractDocument doc = (AbstractDocument)tf.getDocument();
        doc.addDocumentListener(dl);
        doc.setDocumentFilter(vf);
        return tf;
    public static void main(String[] args)
        ValidTransit test = new ValidTransit();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(test.getContent());
        f.setSize(300,140);
        f.setLocation(200,200);
        f.setVisible(true);
class EntryListener extends FocusAdapter
    public void focusGained(FocusEvent e)
        JTextField tf = (JTextField)e.getSource();
        tf.selectAll();
class TransitChecker implements DocumentListener
    public void insertUpdate(DocumentEvent e) { checkLength(e); }
    public void removeUpdate(DocumentEvent e) { checkLength(e); }
    public void changedUpdate(DocumentEvent e) { /* styled text */ }
    private void checkLength(DocumentEvent e)
        if(e.getDocument().getLength() == 1)
            KeyboardFocusManager.getCurrentKeyboardFocusManager().focusNextComponent();
class ValidFilter extends DocumentFilter
    String domain = "0123456789";
    public void insertString(DocumentFilter.FilterBypass fb,
                             int offset,
                             String str,
                             AttributeSet attrs) throws BadLocationException
        replace(fb, offset, 0, str, attrs);
    public void replace(DocumentFilter.FilterBypass fb,
                        int offset,
                        int length,               // selected text
                        String str,               // incoming string
                        AttributeSet attrs) throws BadLocationException
        char[] source = str.toCharArray();
        char[] result = new char[source.length];
        int k = 0;
        for(int j = 0; j < source.length; j++)
            if(domain.indexOf(source[j]) != -1)
                result[k++] = source[j];
            else
                Toolkit.getDefaultToolkit().beep();
        fb.replace(offset, length, new String(result, 0, k), attrs);
}