Searchable JComboBox

The following code can be used to produce a searchable JComboBox. As the user types her selection, the control will search through the list of options and find the closest match, filling in the remaining characters in a user-friendly way. It’s much better control than the default JComboBox, IMO.

This control is highly efficient, and can be used for models with huge numbers of elements. It uses a TernarySearchTree to implement the search forward behavior, which is incredibly fast and memory efficient. All of the classes used by JSearchableComboBox are part of the standard Java distribution except TernarySearchTree, which is provided in the article resources section of the TST link above.

What’s new?

- 2002.10.3 – Added getItem override in custom editor to improve support for putting non-string objects into the combo box.

- 2002.10.8 – Improved ActionEvent handling to avoid deselecting text at incorrect times

JSearchableComboBox.java:

import javax.swing.JComboBox;

import javax.swing.ComboBoxModel;

import java.awt.event.KeyEvent;

import java.awt.event.KeyAdapter;

import java.awt.event.ActionListener;

import java.awt.event.ActionEvent;

import javax.swing.plaf.basic.BasicComboBoxEditor;

/**

* Enables efficient searching through a JComboBox.

* Based on code by Ron (rmlchan@yahoo.com)

*

* @author Eric Lindauer

* @date 2002.9.24

*/

public class JSearchableComboBox extends JComboBox {

public JSearchableComboBox () {

super();

init();

}

public JSearchableComboBox (Object[] elements) {

super(elements);

init();

}

public void setModel (ComboBoxModel model)

{

super.setModel (model);

init ();

}

private void init () {

setEditable(true);

setEditor(new SearchEditor (this));

}

private static class SearchEditor extends BasicComboBoxEditor {

private TernarySearchTree _data = new TernarySearchTree ();

public Object getItem () {

return _data.get (super.getItem ().toString ());

}

public SearchEditor (final JSearchableComboBox cb) {

// populate the search tree with the items in the list

ComboBoxModel model = cb.getModel ();

for (int i = 0; i < model.getSize (); i++)

{

Object data = model.getElementAt (i);

_data.put (data.toString (), data);

}

// when the user types, search the data and guess what they want

KeyAdapter listener = new KeyAdapter () {

public void keyReleased (KeyEvent ev) {

if ((ev.getKeyChar () >= 'a' && ev.getKeyChar () <= 'z') ||

(ev.getKeyChar () >= '0' && ev.getKeyChar () <= '9') ||

(ev.getKeyChar () >= 'A' && ev.getKeyChar () <= 'Z') ||

(ev.getKeyChar () == KeyEvent.VK_SPACE))

{

String startText = editor.getText ();

// cb.showPopup (); ß uncomment for smaller data sets

String finalText = _data.matchPrefixString (startText, 1);

if (finalText.equals (""))

finalText = startText;

if (! finalText.equals (startText))

{

editor.setText (finalText);

editor.setSelectionStart (startText.length ());

editor.setSelectionEnd (finalText.length ());

}

cb.setSelectedItem (_data.get (finalText));

}

}

};

editor.addKeyListener (listener);

// register an action listener to keep the text area always up-to-date

ActionListener actionListener = new ActionListener () {

public void actionPerformed (ActionEvent e)

{

if (cb.getSelectedItem () != null &&

! editor.getText ().equals (cb.getSelectedItem ().toString ()))

{

editor.setText (cb.getSelectedItem ().toString ());

}

}

};

cb.addActionListener (actionListener);

}

}

public static void main(String[] args) {

java.awt.Frame f = new java.awt.Frame();

f.addWindowListener(new java.awt.event.WindowAdapter() {

public void windowClosing(java.awt.event.WindowEvent ev) {

System.exit(0);

}

}

);

String[] stuff = new String[] {"first", "second", "second and some",

"third", "three", "three+", "thrice", "four", "four-plus"};

JSearchableComboBox cb = new JSearchableComboBox (stuff);

f.add(cb);

f.pack();

f.show();

}

} 

Send questions, comments, complaints or compliments to eric@achess.com.

Yours,

Eric Lindauer