import java.awt.*;import javax.swing.*;import javax.swing.event.*;import javax.swing.text.*;import java.util.*;import java.util.regex.*;public class CompletableJTextField extends JTextField    implements ListSelectionListener {    Completer completer;    JList completionList;    DefaultListModel completionListModel;    JScrollPane listScroller;    JWindow listWindow;    public CompletableJTextField (int col) {        super (col);        completer = new Completer();        completionListModel = new DefaultListModel();        completionList = new JList(completionListModel);        completionList.setSelectionMode (ListSelectionModel.SINGLE_SELECTION);        completionList.addListSelectionListener (this);        listScroller =            new JScrollPane (completionList,                              ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,                             ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);        listWindow = new JWindow();        listWindow.getContentPane().add (listScroller);    }    public void addCompletion (String s) {        completer.addCompletion (s); }    public void removeCompletion (String s) {        completer.removeCompletion (s); }    public void clearCompletions (String s ) {        completer.clearCompletions (); }    public void valueChanged (ListSelectionEvent e) {        if (e.getValueIsAdjusting()) { return; }        if (completionList.getModel().getSize() == 0) {return;}        listWindow.setVisible (false);        /*        String completionString =             (String) completionList.getSelectedValue();        // this causes an IllegalStateException:        // "Attempt to mutate in notification"        setText (completionString);        */        final String completionString =            (String) completionList.getSelectedValue();        Thread worker = new Thread() {                public void run() {                    setText (completionString);                }            };        SwingUtilities.invokeLater (worker);    }    /** inner class does the matching of the JTextField's        document to completion strings kept in an ArrayList     */    class Completer implements DocumentListener {        private Pattern pattern;        private ArrayList completions;        public Completer() {            completions = new ArrayList();            getDocument().addDocumentListener (this);        }        public void addCompletion (String s) {            completions.add (s);            buildAndShowPopup();        }                public void removeCompletion (String s) {            completions.remove (s);            buildAndShowPopup();                }                public void clearCompletions () {            completions.clear();            buildPopup();            listWindow.setVisible(false);        }                private void buildPopup() {            completionListModel.clear();            System.out.println ("buildPopup for " + completions.size() +                                " completions");            Iterator it = completions.iterator();            pattern = Pattern.compile (getText() + ".+");            while (it.hasNext()) {                // check if match                String completion = (String) it.next();                Matcher matcher = pattern.matcher (completion);                if (matcher.matches()) {                    // add if match                    System.out.println ("matched "+ completion);                    completionListModel.add (completionListModel.getSize(),                                             completion);                } else {                    System.out.println ("pattern " +                                         pattern.pattern() +                                        " does not match " +                                         completion);                }            }        }        private void showPopup() {            if (completionListModel.getSize() == 0) {                listWindow.setVisible(false);                return;            }            // figure out where the text field is,            // and where its bottom left is            java.awt.Point los = getLocationOnScreen();            int popX = los.x;            int popY = los.y + getHeight();            listWindow.setLocation (popX, popY);            listWindow.pack();            listWindow.setVisible(true);        }        private void buildAndShowPopup() {            if (getText().length() < 1)                return;            buildPopup();            showPopup();        }        // DocumentListener implementation        public void insertUpdate (DocumentEvent e) { buildAndShowPopup(); }        public void removeUpdate (DocumentEvent e) { buildAndShowPopup(); }        public void changedUpdate (DocumentEvent e) { buildAndShowPopup(); }    }}