import java.awt.*;import java.awt.event.*;import javax.swing.*;public class TestRegexConstrainedDocument extends JPanel     implements ActionListener {    JTextField regexField, filterField;    JButton regexButton;    RegexConstrainedDocument regexDoc;    public TestRegexConstrainedDocument() {        setLayout (new BoxLayout (this, BoxLayout.Y_AXIS));        // top - regex stuff        JPanel topPanel = new JPanel();        JLabel rLabel = new JLabel ("regex:" );        topPanel.add (rLabel);        regexField = new JTextField (20);        topPanel.add(regexField);        regexButton = new JButton ("Set");        regexButton.addActionListener (this);        topPanel.add (regexButton);        add (topPanel);        // bottom - filterfield        regexDoc =            new RegexConstrainedDocument ();        filterField = new JTextField (regexDoc, "",  50);        add (filterField);    }    public void actionPerformed (ActionEvent e) {        System.out.println ("actionperformed");        if (e.getSource() == regexButton) {            System.out.println ("regexbutton");            regexDoc.setPatternByString (regexField.getText());        }    }    public static void main (String[] args) {        JComponent c = new TestRegexConstrainedDocument();        JFrame f = new JFrame ("Regex filtering");        f.getContentPane().add (c);        f.pack();        f.setVisible(true);    }}