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JComboBox: adding automatic completion-Backspace 2

JComboBox: adding automatic completion-Backspace 2

//Code from: http://www.orbital-computer.de/JComboBox/
Inside JComboBox: adding automatic completion

Author: Thomas Bierhance

You will have noticed that the method has been called on every key stroke whether you hit 
backspace or not. This happens because the selected text will always be removed before 
inserting a new letter!

Now, when should the selection move backwards and when should some text really be removed? 
Inside the remove method the information is needed if it was called because the user hit 
backspace or if it has been called for other reasons. There already is a KeyListener on the 
combo box' editor, so a boolean member variable named hitBackspace can be introduced that 
indicates whether the last key that has been pressed was backspace or not...

import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;

public class S14KeyListener extends PlainDocument {
    JComboBox comboBox;
    ComboBoxModel model;
    JTextComponent editor;
    // flag to indicate if setSelectedItem has been called
    // subsequent calls to remove/insertString should be ignored
    boolean selecting=false;
    boolean hidePopupOnFocusLoss;
    boolean hitBackspace=false;
    public S14KeyListener(final JComboBox comboBox) {
        this.comboBox = comboBox;
        model = comboBox.getModel();
        editor = (JTextComponent) comboBox.getEditor().getEditorComponent();
        comboBox.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!selecting) highlightCompletedText(0);
        editor.addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent e) {
                if (comboBox.isDisplayable()) comboBox.setPopupVisible(true);
                if (e.getKeyCode()==KeyEvent.VK_BACK_SPACE) hitBackspace=true;
        // Bug 5100422 on Java 1.5: Editable JComboBox won't hide popup when tabbing out
        // Highlight whole text when gaining focus
        editor.addFocusListener(new FocusAdapter() {
            public void focusGained(FocusEvent e) {
            public void focusLost(FocusEvent e) {
                // Workaround for Bug 5100422 - Hide Popup on focus loss
                if (hidePopupOnFocusLoss) comboBox.setPopupVisible(false);
        // Handle initially selected object
        Object selected = comboBox.getSelectedItem();
        if (selected!=null) setText(selected.toString());
    public void remove(int offs, int len) throws BadLocationException {
        // return immediately when selecting an item
        if (selecting) return;
        if (hitBackspace) {
            System.out.println("Backspace was hit: moving the selection backwards");
            // user hit backspace => move the selection backwards
            // old item keeps being selected
        } else {
            System.out.println("Real remove: delegating to super.remove(" + offs + "," + len + ")");
            super.remove(offs, len);
    public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
        // return immediately when selecting an item
        if (selecting) return;
        // insert the string into the document
        super.insertString(offs, str, a);
        // lookup and select a matching item
        Object item = lookupItem(getText(0, getLength()));
        if (item != null) {
        } else {
            // keep old item selected if there is no match
            item = comboBox.getSelectedItem();
            // imitate no insert (later on offs will be incremented by str.length(): selection won't move forward)
            offs = offs-str.length();
            // provide feedback to the user that his input has been received but can not be accepted
            comboBox.getToolkit().beep(); // when available use: UIManager.getLookAndFeel().provideErrorFeedback(comboBox);
        // select the completed part
    private void setText(String text) {
        try {
            // remove all text and insert the completed string
            super.remove(0, getLength());
            super.insertString(0, text, null);
        } catch (BadLocationException e) {
            throw new RuntimeException(e.toString());
    private void highlightCompletedText(int start) {
    private void setSelectedItem(Object item) {
        selecting = true;
        selecting = false;
    private Object lookupItem(String pattern) {
        Object selectedItem = model.getSelectedItem();
        // only search for a different item if the currently selected does not match
        if (selectedItem != null && startsWithIgnoreCase(selectedItem.toString(), pattern)) {
            return selectedItem;
        } else {
            // iterate over all items
            for (int i=0, n=model.getSize(); i < n; i++) {
                Object currentItem = model.getElementAt(i);
                // current item starts with the pattern?
                if (startsWithIgnoreCase(currentItem.toString(), pattern)) {
                    return currentItem;
        // no item starts with the pattern => return null
        return null;
    // checks if str1 starts with str2 - ignores case
    private boolean startsWithIgnoreCase(String str1, String str2) {
        return str1.toUpperCase().startsWith(str2.toUpperCase());
    private static void createAndShowGUI() {
        // the combo box (add/modify items if you like to)
        JComboBox comboBox = new JComboBox(new Object[] {"Ester", "Jordi", "Jordina", "Jorge", "Sergi"});
        // has to be editable
        // change the editor's document
        new S14KeyListener(comboBox);
        // create and show a window containing the combo box
        JFrame frame = new JFrame();
        frame.pack(); frame.setVisible(true);
    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {


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