ItemChooser : Item Chooser « Swing Components « Java


 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;
import java.util.Iterator;

import javax.swing.BoxLayout;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JScrollPane;
import javax.swing.border.EtchedBorder;
import javax.swing.border.TitledBorder;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

 * This class is a Swing component that presents a choice to the user. It allows
 * the choice to be presented in a JList, in a JComboBox, or with a bordered
 * group of JRadioButton components. Additionally, it displays the name of the
 * choice with a JLabel. It allows an arbitrary value to be associated with each
 * possible choice. Note that this component only allows one item to be selected
 * at a time. Multiple selections are not supported.
public class ItemChooser extends JPanel {
  // These fields hold property values for this component
  String name; // The overall name of the choice

  String[] labels; // The text for each choice option

  Object[] values; // Arbitrary values associated with each option

  int selection; // The selected choice

  int presentation; // How the choice is presented

  // These are the legal values for the presentation field
  public static final int LIST = 1;

  public static final int COMBOBOX = 2;

  public static final int RADIOBUTTONS = 3;

  // These components are used for each of the 3 possible presentations
  JList list; // One type of presentation

  JComboBox combobox; // Another type of presentation

  JRadioButton[] radiobuttons; // Yet another type

  // The list of objects that are interested in our state
  ArrayList listeners = new ArrayList();

  // The constructor method sets everything up
  public ItemChooser(String name, String[] labels, Object[] values,
      int defaultSelection, int presentation) {
    // Copy the constructor arguments to instance fields = name;
    this.labels = labels;
    this.values = values;
    this.selection = defaultSelection;
    this.presentation = presentation;

    // If no values were supplied, use the labels
    if (values == null)
      this.values = labels;

    // Now create content and event handlers based on presentation type
    switch (presentation) {
    case LIST:
    case COMBOBOX:

  // Initialization for JList presentation
  void initList() {
    list = new JList(labels); // Create the list
    list.setSelectedIndex(selection); // Set initial state

    // Handle state changes
    list.addListSelectionListener(new ListSelectionListener() {
      public void valueChanged(ListSelectionEvent e) {;

    // Lay out list and name label vertically
    this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS)); // vertical
    this.add(new JLabel(name)); // Display choice name
    this.add(new JScrollPane(list)); // Add the JList

  // Initialization for JComboBox presentation
  void initComboBox() {
    combobox = new JComboBox(labels); // Create the combo box
//    combobox.setSelectedIndex(selection); // Set initial state

    // Handle changes to the state
    combobox.addItemListener(new ItemListener() {
      public void itemStateChanged(ItemEvent e) {;

    // Lay out combo box and name label horizontally
    this.setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
    this.add(new JLabel(name));

  // Initialization for JRadioButton presentation
  void initRadioButtons() {
    // Create an array of mutually exclusive radio buttons
    radiobuttons = new JRadioButton[labels.length]; // the array
    ButtonGroup radioButtonGroup = new ButtonGroup(); // used for exclusion
    ChangeListener listener = new ChangeListener() { // A shared listener
      public void stateChanged(ChangeEvent e) {
        JRadioButton b = (JRadioButton) e.getSource();
        if (b.isSelected()) {
          // If we received this event because a button was
          // selected, then loop through the list of buttons to
          // figure out the index of the selected one.
          for (int i = 0; i < radiobuttons.length; i++) {
            if (radiobuttons[i] == b) {

    // Display the choice name in a border around the buttons
    this.setBorder(new TitledBorder(new EtchedBorder(), name));
    this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));

    // Create the buttons, add them to the button group, and specify
    // the event listener for each one.
    for (int i = 0; i < labels.length; i++) {
      radiobuttons[i] = new JRadioButton(labels[i]);
      if (i == selection)

  // These simple property accessor methods just return field values
  // These are read-only properties. The values are set by the constructor
  // and may not be changed.
  public String getName() {
    return name;

  public int getPresentation() {
    return presentation;

  public String[] getLabels() {
    return labels;

  public Object[] getValues() {
    return values;

  /** Return the index of the selected item */
  public int getSelectedIndex() {
    return selection;

  /** Return the object associated with the selected item */
  public Object getSelectedValue() {
    return values[selection];

   * Set the selected item by specifying its index. Calling this method
   * changes the on-screen display but does not generate events.
  public void setSelectedIndex(int selection) {
    switch (presentation) {
    case LIST:
    case COMBOBOX:
    this.selection = selection;

   * This internal method is called when the selection changes. It stores the
   * new selected index, and fires events to any registered listeners. The
   * event listeners registered on the JList, JComboBox, or JRadioButtons all
   * call this method.
  protected void select(int selection) {
    this.selection = selection; // Store the new selected index
    if (!listeners.isEmpty()) { // If there are any listeners registered
      // Create an event object to describe the selection
      ItemChooser.Event e = new ItemChooser.Event(this, selection,
      // Loop through the listeners using an Iterator
      for (Iterator i = listeners.iterator(); i.hasNext();) {
        ItemChooser.Listener l = (ItemChooser.Listener);
        l.itemChosen(e); // Notify each listener of the selection

  // These methods are for event listener registration and deregistration
  public void addItemChooserListener(ItemChooser.Listener l) {

  public void removeItemChooserListener(ItemChooser.Listener l) {

   * This inner class defines the event type generated by ItemChooser objects
   * The inner class name is Event, so the full name is ItemChooser.Event
  public static class Event extends java.util.EventObject {
    int selectedIndex; // index of the selected item

    Object selectedValue; // the value associated with it

    public Event(ItemChooser source, int selectedIndex, Object selectedValue) {
      this.selectedIndex = selectedIndex;
      this.selectedValue = selectedValue;

    public ItemChooser getItemChooser() {
      return (ItemChooser) getSource();

    public int getSelectedIndex() {
      return selectedIndex;

    public Object getSelectedValue() {
      return selectedValue;

   * This inner interface must be implemented by any object that wants to be
   * notified when the current selection in a ItemChooser component changes.
  public interface Listener extends java.util.EventListener {
    public void itemChosen(ItemChooser.Event e);

  public static void main(String[] args) {
    // Create a window, arrange to handle close requests
    final JFrame frame = new JFrame("ItemChooser Demo");
    frame.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {

    // A "message line" to display results in
    final JLabel msgline = new JLabel(" ");
    args = new String[]{"a","b","c"};
    // Create a panel holding three ItemChooser components
    JPanel chooserPanel = new JPanel();
    final ItemChooser c1 = new ItemChooser("Choice #1", args, null, 0,
    final ItemChooser c2 = new ItemChooser("Choice #2", args, null, 0,
    final ItemChooser c3 = new ItemChooser("Choice #3", args, null, 0,

    // An event listener that displays changes on the message line
    ItemChooser.Listener l = new ItemChooser.Listener() {
      public void itemChosen(ItemChooser.Event e) {
        msgline.setText(e.getItemChooser().getName() + ": "
            + e.getSelectedIndex() + ": " + e.getSelectedValue());

    // Instead of tracking every change with a ItemChooser.Listener,
    // applications can also just query the current state when
    // they need it. Here's a button that does that.
    JButton report = new JButton("Report");
    report.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        // Note the use of multi-line italic HTML text
        // with the JOptionPane message dialog box.
        String msg = "<html><i>" + c1.getName() + ": "
            + c1.getSelectedValue() + "<br>" + c2.getName() + ": "
            + c2.getSelectedValue() + "<br>" + c3.getName() + ": "
            + c3.getSelectedValue() + "</i>";
        JOptionPane.showMessageDialog(frame, msg);

    // Add the 3 ItemChooser objects, and the Button to the panel

    // Add the panel and the message line to the window
    Container contentPane = frame.getContentPane();
    contentPane.add(chooserPanel, BorderLayout.CENTER);
    contentPane.add(msgline, BorderLayout.SOUTH);

    // Set the window size and pop it up.



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