source: josm/src/org/openstreetmap/josm/tools/AutoCompleteComboBox.java@ 298

// License: GPL. Copyright 2007 by Immanuel Scholz and others
package org.openstreetmap.josm.tools;

import java.util.Collection;

import javax.swing.ComboBoxModel;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.JTextComponent;
import javax.swing.text.PlainDocument;

/**
 * @author guilhem.bonnefille@gmail.com
 */
public class AutoCompleteComboBox extends JComboBox {

        /**
         * Auto-complete a JComboBox.
         * 
         * Inspired by http://www.orbital-computer.de/JComboBox/
         */
        private class AutoCompleteComboBoxDocument extends PlainDocument {
                private JComboBox comboBox;
                private boolean selecting = false;

                public AutoCompleteComboBoxDocument(final JComboBox comboBox) {
                        this.comboBox = comboBox;
                }

                @Override public void remove(int offs, int len) throws BadLocationException {
                        if (selecting)
                                return;
                        super.remove(offs, len);
                }

                @Override public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
                        super.insertString(offs, str, a);

                        // return immediately when selecting an item
                        // Nota: this is done after calling super method because we need
                        // ActionListener informed
                        if (selecting)
                                return;

                        // lookup and select a matching item
                        Object item = lookupItem(getText(0, getLength()));
                        if (item != null) {
                                // remove all text and insert the completed string
                                super.remove(0, getLength());
                                super.insertString(0, item.toString(), a);
                                // select the completed part
                                JTextComponent editor = (JTextComponent)comboBox.getEditor().getEditorComponent();
                                editor.setSelectionStart(offs + str.length());
                                editor.setSelectionEnd(getLength());
                        }
                        setSelectedItem(item);
                }

                private void setSelectedItem(Object item) {
                        selecting = true;
                        comboBox.setSelectedItem(item);
                        selecting = false;
                }

                private Object lookupItem(String pattern) {
                        ComboBoxModel model = comboBox.getModel();
                        for (int i = 0, n = model.getSize(); i < n; i++) {
                                Object currentItem = model.getElementAt(i);
                                if (currentItem.toString().startsWith(pattern))
                                        return currentItem;
                        }
                        return null;
                }
        }

        public AutoCompleteComboBox() {
                JTextComponent editor = (JTextComponent) this.getEditor().getEditorComponent();
                editor.setDocument(new AutoCompleteComboBoxDocument(this));
        }

        public void setPossibleItems(Collection<String> elems) {
                Object oldValue = this.getSelectedItem();
                DefaultComboBoxModel model = (DefaultComboBoxModel)this.getModel();
                model.removeAllElements();
                for (String elem : elems) model.addElement(elem);
                this.setSelectedItem(oldValue);
                this.getEditor().selectAll();
        }
}