1 /*
   2  * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package javax.swing;
  26 
  27 import java.awt.Component;
  28 import java.awt.Graphics;
  29 import java.awt.Insets;
  30 import java.awt.event.*;
  31 import java.beans.JavaBean;
  32 import java.beans.BeanProperty;
  33 import java.beans.Transient;
  34 import java.util.Vector;
  35 
  36 import java.io.Serializable;
  37 import java.io.ObjectOutputStream;
  38 import java.io.ObjectInputStream;
  39 import java.io.IOException;
  40 
  41 import javax.swing.plaf.*;
  42 import javax.accessibility.*;
  43 
  44 /**
  45  * An implementation of a menu bar. You add <code>JMenu</code> objects to the
  46  * menu bar to construct a menu. When the user selects a <code>JMenu</code>
  47  * object, its associated <code>JPopupMenu</code> is displayed, allowing the
  48  * user to select one of the <code>JMenuItems</code> on it.
  49  * <p>
  50  * For information and examples of using menu bars see
  51  * <a
  52  href="http://docs.oracle.com/javase/tutorial/uiswing/components/menu.html">How to Use Menus</a>,
  53  * a section in <em>The Java Tutorial.</em>
  54  * <p>
  55  * <strong>Warning:</strong> Swing is not thread safe. For more
  56  * information see <a
  57  * href="package-summary.html#threading">Swing's Threading
  58  * Policy</a>.
  59  * <p>
  60  * <strong>Warning:</strong>
  61  * Serialized objects of this class will not be compatible with
  62  * future Swing releases. The current serialization support is
  63  * appropriate for short term storage or RMI between applications running
  64  * the same version of Swing.  As of 1.4, support for long term storage
  65  * of all JavaBeans&trade;
  66  * has been added to the <code>java.beans</code> package.
  67  * Please see {@link java.beans.XMLEncoder}.
  68  * <p>
  69  * <strong>Warning:</strong>
  70  * By default, pressing the Tab key does not transfer focus from a <code>
  71  * JMenuBar</code> which is added to a container together with other Swing
  72  * components, because the <code>focusTraversalKeysEnabled</code> property
  73  * of <code>JMenuBar</code> is set to <code>false</code>. To resolve this,
  74  * you should call the <code>JMenuBar.setFocusTraversalKeysEnabled(true)</code>
  75  * method.
  76  *
  77  * @author Georges Saab
  78  * @author David Karlton
  79  * @author Arnaud Weber
  80  * @see JMenu
  81  * @see JPopupMenu
  82  * @see JMenuItem
  83  * @since 1.2
  84  */
  85 @JavaBean(defaultProperty = "UI", description = "A container for holding and displaying menus.")
  86 @SwingContainer
  87 @SuppressWarnings("serial")
  88 public class JMenuBar extends JComponent implements Accessible,MenuElement
  89 {
  90     /**
  91      * @see #getUIClassID
  92      * @see #readObject
  93      */
  94     private static final String uiClassID = "MenuBarUI";
  95 
  96     /*
  97      * Model for the selected subcontrol.
  98      */
  99     private transient SingleSelectionModel selectionModel;
 100 
 101     private boolean paintBorder           = true;
 102     private Insets     margin             = null;
 103 
 104     /* diagnostic aids -- should be false for production builds. */
 105     private static final boolean TRACE =   false; // trace creates and disposes
 106     private static final boolean VERBOSE = false; // show reuse hits/misses
 107     private static final boolean DEBUG =   false;  // show bad params, misc.
 108 
 109     /**
 110      * Creates a new menu bar.
 111      */
 112     public JMenuBar() {
 113         super();
 114         setFocusTraversalKeysEnabled(false);
 115         setSelectionModel(new DefaultSingleSelectionModel());
 116         updateUI();
 117     }
 118 
 119     /**
 120      * Returns the menubar's current UI.
 121      *
 122      * @return a {@code MenuBarUI} which is the menubar's current L&amp;F object
 123      * @see #setUI
 124      */
 125     public MenuBarUI getUI() {
 126         return (MenuBarUI)ui;
 127     }
 128 
 129     /**
 130      * Sets the L&amp;F object that renders this component.
 131      *
 132      * @param ui the new MenuBarUI L&amp;F object
 133      * @see UIDefaults#getUI
 134      */
 135     @BeanProperty(hidden = true, visualUpdate = true, description
 136             = "The UI object that implements the Component's LookAndFeel.")
 137     public void setUI(MenuBarUI ui) {
 138         super.setUI(ui);
 139     }
 140 
 141     /**
 142      * Resets the UI property with a value from the current look and feel.
 143      *
 144      * @see JComponent#updateUI
 145      */
 146     public void updateUI() {
 147         setUI((MenuBarUI)UIManager.getUI(this));
 148     }
 149 
 150 
 151     /**
 152      * Returns the name of the L&amp;F class that renders this component.
 153      *
 154      * @return the string "MenuBarUI"
 155      * @see JComponent#getUIClassID
 156      * @see UIDefaults#getUI
 157      */
 158     @BeanProperty(bound = false)
 159     public String getUIClassID() {
 160         return uiClassID;
 161     }
 162 
 163 
 164     /**
 165      * Returns the model object that handles single selections.
 166      *
 167      * @return the <code>SingleSelectionModel</code> property
 168      * @see SingleSelectionModel
 169      */
 170     public SingleSelectionModel getSelectionModel() {
 171         return selectionModel;
 172     }
 173 
 174     /**
 175      * Sets the model object to handle single selections.
 176      *
 177      * @param model the <code>SingleSelectionModel</code> to use
 178      * @see SingleSelectionModel
 179      */
 180     @BeanProperty(description = "The selection model, recording which child is selected.")
 181     public void setSelectionModel(SingleSelectionModel model) {
 182         SingleSelectionModel oldValue = selectionModel;
 183         this.selectionModel = model;
 184         firePropertyChange("selectionModel", oldValue, selectionModel);
 185     }
 186 
 187 
 188     /**
 189      * Appends the specified menu to the end of the menu bar.
 190      *
 191      * @param c the <code>JMenu</code> component to add
 192      * @return the menu component
 193      */
 194     public JMenu add(JMenu c) {
 195         super.add(c);
 196         return c;
 197     }
 198 
 199     /**
 200      * Returns the menu at the specified position in the menu bar.
 201      *
 202      * @param index  an integer giving the position in the menu bar, where
 203      *               0 is the first position
 204      * @return the <code>JMenu</code> at that position, or <code>null</code> if
 205      *          if there is no <code>JMenu</code> at that position (ie. if
 206      *          it is a <code>JMenuItem</code>)
 207      */
 208     public JMenu getMenu(int index) {
 209         Component c = getComponentAtIndex(index);
 210         if (c instanceof JMenu)
 211             return (JMenu) c;
 212         return null;
 213     }
 214 
 215     /**
 216      * Returns the number of items in the menu bar.
 217      *
 218      * @return the number of items in the menu bar
 219      */
 220     @BeanProperty(bound = false)
 221     public int getMenuCount() {
 222         return getComponentCount();
 223     }
 224 
 225     /**
 226      * Sets the help menu that appears when the user selects the
 227      * "help" option in the menu bar. This method is not yet implemented
 228      * and will throw an exception.
 229      *
 230      * @param menu the JMenu that delivers help to the user
 231      */
 232     public void setHelpMenu(JMenu menu) {
 233         throw new Error("setHelpMenu() not yet implemented.");
 234     }
 235 
 236     /**
 237      * Gets the help menu for the menu bar.  This method is not yet
 238      * implemented and will throw an exception.
 239      *
 240      * @return the <code>JMenu</code> that delivers help to the user
 241      */
 242     @Transient
 243     public JMenu getHelpMenu() {
 244         throw new Error("getHelpMenu() not yet implemented.");
 245     }
 246 
 247     /**
 248      * Returns the component at the specified index.
 249      *
 250      * @param i an integer specifying the position, where 0 is first
 251      * @return the <code>Component</code> at the position,
 252      *          or <code>null</code> for an invalid index
 253      * @deprecated replaced by <code>getComponent(int i)</code>
 254      */
 255     @Deprecated
 256     public Component getComponentAtIndex(int i) {
 257         if(i < 0 || i >= getComponentCount()) {
 258             return null;
 259         }
 260         return getComponent(i);
 261     }
 262 
 263     /**
 264      * Returns the index of the specified component.
 265      *
 266      * @param c  the <code>Component</code> to find
 267      * @return an integer giving the component's position, where 0 is first;
 268      *          or -1 if it can't be found
 269      */
 270     public int getComponentIndex(Component c) {
 271         int ncomponents = this.getComponentCount();
 272         Component[] component = this.getComponents();
 273         for (int i = 0 ; i < ncomponents ; i++) {
 274             Component comp = component[i];
 275             if (comp == c)
 276                 return i;
 277         }
 278         return -1;
 279     }
 280 
 281     /**
 282      * Sets the currently selected component, producing a
 283      * a change to the selection model.
 284      *
 285      * @param sel the <code>Component</code> to select
 286      */
 287     public void setSelected(Component sel) {
 288         SingleSelectionModel model = getSelectionModel();
 289         int index = getComponentIndex(sel);
 290         model.setSelectedIndex(index);
 291     }
 292 
 293     /**
 294      * Returns true if the menu bar currently has a component selected.
 295      *
 296      * @return true if a selection has been made, else false
 297      */
 298     @BeanProperty(bound = false)
 299     public boolean isSelected() {
 300         return selectionModel.isSelected();
 301     }
 302 
 303     /**
 304      * Returns true if the menu bars border should be painted.
 305      *
 306      * @return  true if the border should be painted, else false
 307      */
 308     public boolean isBorderPainted() {
 309         return paintBorder;
 310     }
 311 
 312     /**
 313      * Sets whether the border should be painted.
 314      *
 315      * @param b if true and border property is not <code>null</code>,
 316      *          the border is painted.
 317      * @see #isBorderPainted
 318      */
 319     @BeanProperty(visualUpdate = true, description
 320             = "Whether the border should be painted.")
 321     public void setBorderPainted(boolean b) {
 322         boolean oldValue = paintBorder;
 323         paintBorder = b;
 324         firePropertyChange("borderPainted", oldValue, paintBorder);
 325         if (b != oldValue) {
 326             revalidate();
 327             repaint();
 328         }
 329     }
 330 
 331     /**
 332      * Paints the menubar's border if <code>BorderPainted</code>
 333      * property is true.
 334      *
 335      * @param g the <code>Graphics</code> context to use for painting
 336      * @see JComponent#paint
 337      * @see JComponent#setBorder
 338      */
 339     protected void paintBorder(Graphics g) {
 340         if (isBorderPainted()) {
 341             super.paintBorder(g);
 342         }
 343     }
 344 
 345     /**
 346      * Sets the margin between the menubar's border and
 347      * its menus. Setting to <code>null</code> will cause the menubar to
 348      * use the default margins.
 349      *
 350      * @param m an Insets object containing the margin values
 351      * @see Insets
 352      */
 353     @BeanProperty(visualUpdate = true, description
 354             = "The space between the menubar's border and its contents")
 355     public void setMargin(Insets m) {
 356         Insets old = margin;
 357         this.margin = m;
 358         firePropertyChange("margin", old, m);
 359         if (old == null || !old.equals(m)) {
 360             revalidate();
 361             repaint();
 362         }
 363     }
 364 
 365     /**
 366      * Returns the margin between the menubar's border and
 367      * its menus.  If there is no previous margin, it will create
 368      * a default margin with zero size.
 369      *
 370      * @return an <code>Insets</code> object containing the margin values
 371      * @see Insets
 372      */
 373     public Insets getMargin() {
 374         if(margin == null) {
 375             return new Insets(0,0,0,0);
 376         } else {
 377             return margin;
 378         }
 379     }
 380 
 381 
 382     /**
 383      * Implemented to be a <code>MenuElement</code> -- does nothing.
 384      *
 385      * @see #getSubElements
 386      */
 387     public void processMouseEvent(MouseEvent event,MenuElement path[],MenuSelectionManager manager) {
 388     }
 389 
 390     /**
 391      * Implemented to be a <code>MenuElement</code> -- does nothing.
 392      *
 393      * @see #getSubElements
 394      */
 395     public void processKeyEvent(KeyEvent e,MenuElement path[],MenuSelectionManager manager) {
 396     }
 397 
 398     /**
 399      * Implemented to be a <code>MenuElement</code> -- does nothing.
 400      *
 401      * @see #getSubElements
 402      */
 403     public void menuSelectionChanged(boolean isIncluded) {
 404     }
 405 
 406     /**
 407      * Implemented to be a <code>MenuElement</code> -- returns the
 408      * menus in this menu bar.
 409      * This is the reason for implementing the <code>MenuElement</code>
 410      * interface -- so that the menu bar can be treated the same as
 411      * other menu elements.
 412      * @return an array of menu items in the menu bar.
 413      */
 414     @BeanProperty(bound = false)
 415     public MenuElement[] getSubElements() {
 416         MenuElement result[];
 417         Vector<MenuElement> tmp = new Vector<MenuElement>();
 418         int c = getComponentCount();
 419         int i;
 420         Component m;
 421 
 422         for(i=0 ; i < c ; i++) {
 423             m = getComponent(i);
 424             if(m instanceof MenuElement)
 425                 tmp.addElement((MenuElement) m);
 426         }
 427 
 428         result = new MenuElement[tmp.size()];
 429         for(i=0,c=tmp.size() ; i < c ; i++)
 430             result[i] = tmp.elementAt(i);
 431         return result;
 432     }
 433 
 434     /**
 435      * Implemented to be a <code>MenuElement</code>. Returns this object.
 436      *
 437      * @return the current <code>Component</code> (this)
 438      * @see #getSubElements
 439      */
 440     public Component getComponent() {
 441         return this;
 442     }
 443 
 444 
 445     /**
 446      * Returns a string representation of this <code>JMenuBar</code>.
 447      * This method
 448      * is intended to be used only for debugging purposes, and the
 449      * content and format of the returned string may vary between
 450      * implementations. The returned string may be empty but may not
 451      * be <code>null</code>.
 452      *
 453      * @return  a string representation of this <code>JMenuBar</code>
 454      */
 455     protected String paramString() {
 456         String paintBorderString = (paintBorder ?
 457                                     "true" : "false");
 458         String marginString = (margin != null ?
 459                                margin.toString() : "");
 460 
 461         return super.paramString() +
 462         ",margin=" + marginString +
 463         ",paintBorder=" + paintBorderString;
 464     }
 465 
 466 /////////////////
 467 // Accessibility support
 468 ////////////////
 469 
 470     /**
 471      * Gets the AccessibleContext associated with this JMenuBar.
 472      * For JMenuBars, the AccessibleContext takes the form of an
 473      * AccessibleJMenuBar.
 474      * A new AccessibleJMenuBar instance is created if necessary.
 475      *
 476      * @return an AccessibleJMenuBar that serves as the
 477      *         AccessibleContext of this JMenuBar
 478      */
 479     @BeanProperty(bound = false)
 480     public AccessibleContext getAccessibleContext() {
 481         if (accessibleContext == null) {
 482             accessibleContext = new AccessibleJMenuBar();
 483         }
 484         return accessibleContext;
 485     }
 486 
 487     /**
 488      * This class implements accessibility support for the
 489      * <code>JMenuBar</code> class.  It provides an implementation of the
 490      * Java Accessibility API appropriate to menu bar user-interface
 491      * elements.
 492      * <p>
 493      * <strong>Warning:</strong>
 494      * Serialized objects of this class will not be compatible with
 495      * future Swing releases. The current serialization support is
 496      * appropriate for short term storage or RMI between applications running
 497      * the same version of Swing.  As of 1.4, support for long term storage
 498      * of all JavaBeans&trade;
 499      * has been added to the <code>java.beans</code> package.
 500      * Please see {@link java.beans.XMLEncoder}.
 501      */
 502     @SuppressWarnings("serial")
 503     protected class AccessibleJMenuBar extends AccessibleJComponent
 504         implements AccessibleSelection {
 505 
 506         /**
 507          * Get the accessible state set of this object.
 508          *
 509          * @return an instance of AccessibleState containing the current state
 510          *         of the object
 511          */
 512         public AccessibleStateSet getAccessibleStateSet() {
 513             AccessibleStateSet states = super.getAccessibleStateSet();
 514             return states;
 515         }
 516 
 517         /**
 518          * Get the role of this object.
 519          *
 520          * @return an instance of AccessibleRole describing the role of the
 521          * object
 522          */
 523         public AccessibleRole getAccessibleRole() {
 524             return AccessibleRole.MENU_BAR;
 525         }
 526 
 527         /**
 528          * Get the AccessibleSelection associated with this object.  In the
 529          * implementation of the Java Accessibility API for this class,
 530          * return this object, which is responsible for implementing the
 531          * AccessibleSelection interface on behalf of itself.
 532          *
 533          * @return this object
 534          */
 535         public AccessibleSelection getAccessibleSelection() {
 536             return this;
 537         }
 538 
 539         /**
 540          * Returns 1 if a menu is currently selected in this menu bar.
 541          *
 542          * @return 1 if a menu is currently selected, else 0
 543          */
 544          public int getAccessibleSelectionCount() {
 545             if (isSelected()) {
 546                 return 1;
 547             } else {
 548                 return 0;
 549             }
 550          }
 551 
 552         /**
 553          * Returns the currently selected menu if one is selected,
 554          * otherwise null.
 555          */
 556          public Accessible getAccessibleSelection(int i) {
 557             if (isSelected()) {
 558                 if (i != 0) {   // single selection model for JMenuBar
 559                     return null;
 560                 }
 561                 int j = getSelectionModel().getSelectedIndex();
 562                 if (getComponentAtIndex(j) instanceof Accessible) {
 563                     return (Accessible) getComponentAtIndex(j);
 564                 }
 565             }
 566             return null;
 567          }
 568 
 569         /**
 570          * Returns true if the current child of this object is selected.
 571          *
 572          * @param i the zero-based index of the child in this Accessible
 573          * object.
 574          * @see AccessibleContext#getAccessibleChild
 575          */
 576         public boolean isAccessibleChildSelected(int i) {
 577             return (i == getSelectionModel().getSelectedIndex());
 578         }
 579 
 580         /**
 581          * Selects the nth menu in the menu bar, forcing it to
 582          * pop up.  If another menu is popped up, this will force
 583          * it to close.  If the nth menu is already selected, this
 584          * method has no effect.
 585          *
 586          * @param i the zero-based index of selectable items
 587          * @see #getAccessibleStateSet
 588          */
 589         public void addAccessibleSelection(int i) {
 590             // first close up any open menu
 591             int j = getSelectionModel().getSelectedIndex();
 592             if (i == j) {
 593                 return;
 594             }
 595             if (j >= 0 && j < getMenuCount()) {
 596                 JMenu menu = getMenu(j);
 597                 if (menu != null) {
 598                     MenuSelectionManager.defaultManager().setSelectedPath(null);
 599 //                  menu.setPopupMenuVisible(false);
 600                 }
 601             }
 602             // now popup the new menu
 603             getSelectionModel().setSelectedIndex(i);
 604             JMenu menu = getMenu(i);
 605             if (menu != null) {
 606                 MenuElement me[] = new MenuElement[3];
 607                 me[0] = JMenuBar.this;
 608                 me[1] = menu;
 609                 me[2] = menu.getPopupMenu();
 610                 MenuSelectionManager.defaultManager().setSelectedPath(me);
 611 //              menu.setPopupMenuVisible(true);
 612             }
 613         }
 614 
 615         /**
 616          * Removes the nth selected item in the object from the object's
 617          * selection.  If the nth item isn't currently selected, this
 618          * method has no effect.  Otherwise, it closes the popup menu.
 619          *
 620          * @param i the zero-based index of selectable items
 621          */
 622         public void removeAccessibleSelection(int i) {
 623             if (i >= 0 && i < getMenuCount()) {
 624                 JMenu menu = getMenu(i);
 625                 if (menu != null) {
 626                     MenuSelectionManager.defaultManager().setSelectedPath(null);
 627 //                  menu.setPopupMenuVisible(false);
 628                 }
 629                 getSelectionModel().setSelectedIndex(-1);
 630             }
 631         }
 632 
 633         /**
 634          * Clears the selection in the object, so that nothing in the
 635          * object is selected.  This will close any open menu.
 636          */
 637         public void clearAccessibleSelection() {
 638             int i = getSelectionModel().getSelectedIndex();
 639             if (i >= 0 && i < getMenuCount()) {
 640                 JMenu menu = getMenu(i);
 641                 if (menu != null) {
 642                     MenuSelectionManager.defaultManager().setSelectedPath(null);
 643 //                  menu.setPopupMenuVisible(false);
 644                 }
 645             }
 646             getSelectionModel().setSelectedIndex(-1);
 647         }
 648 
 649         /**
 650          * Normally causes every selected item in the object to be selected
 651          * if the object supports multiple selections.  This method
 652          * makes no sense in a menu bar, and so does nothing.
 653          */
 654         public void selectAllAccessibleSelection() {
 655         }
 656     } // internal class AccessibleJMenuBar
 657 
 658 
 659     /**
 660      * Subclassed to check all the child menus.
 661      * @since 1.3
 662      */
 663     protected boolean processKeyBinding(KeyStroke ks, KeyEvent e,
 664                                         int condition, boolean pressed) {
 665         // See if we have a local binding.
 666         boolean retValue = super.processKeyBinding(ks, e, condition, pressed);
 667         if (!retValue) {
 668             MenuElement[] subElements = getSubElements();
 669             for (MenuElement subElement : subElements) {
 670                 if (processBindingForKeyStrokeRecursive(
 671                         subElement, ks, e, condition, pressed)) {
 672                     return true;
 673                 }
 674             }
 675         }
 676         return retValue;
 677     }
 678 
 679     static boolean processBindingForKeyStrokeRecursive(MenuElement elem,
 680                                                        KeyStroke ks, KeyEvent e, int condition, boolean pressed) {
 681         if (elem == null) {
 682             return false;
 683         }
 684 
 685         Component c = elem.getComponent();
 686 
 687         if ( !(c.isVisible() || (c instanceof JPopupMenu)) || !c.isEnabled() ) {
 688             return false;
 689         }
 690 
 691         if (c != null && c instanceof JComponent &&
 692             ((JComponent)c).processKeyBinding(ks, e, condition, pressed)) {
 693 
 694             return true;
 695         }
 696 
 697         MenuElement[] subElements = elem.getSubElements();
 698         for (MenuElement subElement : subElements) {
 699             if (processBindingForKeyStrokeRecursive(subElement, ks, e, condition, pressed)) {
 700                 return true;
 701                 // We don't, pass along to children JMenu's
 702             }
 703         }
 704         return false;
 705     }
 706 
 707     /**
 708      * Overrides <code>JComponent.addNotify</code> to register this
 709      * menu bar with the current keyboard manager.
 710      */
 711     public void addNotify() {
 712         super.addNotify();
 713         KeyboardManager.getCurrentManager().registerMenuBar(this);
 714     }
 715 
 716     /**
 717      * Overrides <code>JComponent.removeNotify</code> to unregister this
 718      * menu bar with the current keyboard manager.
 719      */
 720     public void removeNotify() {
 721         super.removeNotify();
 722         KeyboardManager.getCurrentManager().unregisterMenuBar(this);
 723     }
 724 
 725 
 726     private void writeObject(ObjectOutputStream s) throws IOException {
 727         s.defaultWriteObject();
 728         if (getUIClassID().equals(uiClassID)) {
 729             byte count = JComponent.getWriteObjCounter(this);
 730             JComponent.setWriteObjCounter(this, --count);
 731             if (count == 0 && ui != null) {
 732                 ui.installUI(this);
 733             }
 734         }
 735 
 736         Object[] kvData = new Object[4];
 737         int n = 0;
 738 
 739         if (selectionModel instanceof Serializable) {
 740             kvData[n++] = "selectionModel";
 741             kvData[n++] = selectionModel;
 742         }
 743 
 744         s.writeObject(kvData);
 745     }
 746 
 747 
 748     /**
 749      * See JComponent.readObject() for information about serialization
 750      * in Swing.
 751      */
 752     private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException
 753     {
 754         s.defaultReadObject();
 755         Object[] kvData = (Object[])(s.readObject());
 756 
 757         for(int i = 0; i < kvData.length; i += 2) {
 758             if (kvData[i] == null) {
 759                 break;
 760             }
 761             else if (kvData[i].equals("selectionModel")) {
 762                 selectionModel = (SingleSelectionModel)kvData[i + 1];
 763             }
 764         }
 765 
 766     }
 767 }