001/* MenuComponent.java -- Superclass of all AWT menu components
002   Copyright (C) 1999, 2000, 2002, 2003, 2004, 2005, 2006
003   Free Software Foundation, Inc.
004
005This file is part of GNU Classpath.
006
007GNU Classpath is free software; you can redistribute it and/or modify
008it under the terms of the GNU General Public License as published by
009the Free Software Foundation; either version 2, or (at your option)
010any later version.
011
012GNU Classpath is distributed in the hope that it will be useful, but
013WITHOUT ANY WARRANTY; without even the implied warranty of
014MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015General Public License for more details.
016
017You should have received a copy of the GNU General Public License
018along with GNU Classpath; see the file COPYING.  If not, write to the
019Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02002110-1301 USA.
021
022Linking this library statically or dynamically with other modules is
023making a combined work based on this library.  Thus, the terms and
024conditions of the GNU General Public License cover the whole
025combination.
026
027As a special exception, the copyright holders of this library give you
028permission to link this library with independent modules to produce an
029executable, regardless of the license terms of these independent
030modules, and to copy and distribute the resulting executable under
031terms of your choice, provided that you also meet, for each linked
032independent module, the terms and conditions of the license of that
033module.  An independent module is a module which is not derived from
034or based on this library.  If you modify this library, you may extend
035this exception to your version of the library, but you are not
036obligated to do so.  If you do not wish to do so, delete this
037exception statement from your version. */
038
039
040package java.awt;
041
042import java.awt.event.FocusEvent;
043import java.awt.event.FocusListener;
044import java.awt.peer.MenuComponentPeer;
045import java.io.Serializable;
046import java.util.Locale;
047
048import javax.accessibility.Accessible;
049import javax.accessibility.AccessibleComponent;
050import javax.accessibility.AccessibleContext;
051import javax.accessibility.AccessibleRole;
052import javax.accessibility.AccessibleSelection;
053import javax.accessibility.AccessibleStateSet;
054
055/**
056  * This is the superclass of all menu AWT widgets. 
057  *
058  * @author Aaron M. Renn (arenn@urbanophile.com)
059  * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
060  */
061public abstract class MenuComponent implements Serializable
062{
063
064//Serialization Constant
065  private static final long serialVersionUID = -4536902356223894379L;
066
067  /**
068   * The font for this component.
069   *
070   * @see #getFont()
071   * @see #setFont(java.awt.Font)
072   * @serial the component's font.
073   */
074  private Font font;
075
076  /**
077   * The name of the component.
078   *
079   * @see #getName()
080   * @see #setName(String)
081   * @serial the component's name.
082   */
083  private String name;
084
085  /**
086   * The parent of this component.
087   *
088   * @see #getParent()
089   * @see #setParent(java.awt.MenuContainer)
090   * @serial ignored.
091   */
092  transient MenuContainer parent;
093
094  /**
095   * The native peer for this component.
096   *
097   * @see #getPeer()
098   * @see #setPeer(java.awt.peer.MenuComponentPeer)
099   * @serial ignored.
100   */
101  transient MenuComponentPeer peer;
102
103  /**
104   * The synchronization locking object for this component.
105   *
106   * @serial ignored.
107   */
108  private transient Object tree_lock = this;
109
110  /**
111   * The toolkit for this object.
112   *
113   * @see #getToolkit()
114   * @serial ignored.
115   */
116  private static transient Toolkit toolkit = Toolkit.getDefaultToolkit();
117
118  /**
119   * The accessible context for this component.
120   *
121   * @see #getAccessibleContext()
122   * @serial the accessibility information for this component.
123   */
124  AccessibleContext accessibleContext;
125
126  /**
127   * Was the name of the component set?  This value defaults
128   * to false and becomes true after a call to <code>setName()</code>.
129   * Please note that this does not guarantee that name will then
130   * be non-null, as this may be the value passed to <code>setName()</code>.
131   *
132   * @see #setName(String)
133   * @serial true if the name value has been explicitly set by calling
134   *         <code>setName()</code>.
135   */
136  private boolean nameExplicitlySet;
137
138  /**
139   * Does this component handle new events?  Events will be handled
140   * by this component if this is true.  Otherwise, they will be forwarded
141   * up the component hierarchy.  This implementation does not use this
142   * variable; it is merely provided for serialization compatability.
143   *
144   * @see #dispatchEvent(AWTEvent)
145   * @serial true if events are to be processed locally.  Unused.
146   */
147  private boolean newEventsOnly;
148
149  /**
150   * The focus listener chain handler which deals with focus events for
151   * the accessible context of this component.
152   *
153   * @see AccessibleAWTMenuComponent#addFocusListener(java.awt.event.FocusListener)
154   * @serial ignored.
155   * This is package-private to avoid an accessor method.
156   */
157  transient FocusListener focusListener;
158
159  /**
160   * Default constructor for subclasses.
161   *
162   * @throws HeadlessException ff GraphicsEnvironment.isHeadless() is true
163   */
164  public MenuComponent()
165  {
166    if (GraphicsEnvironment.isHeadless())
167      throw new HeadlessException();
168  }
169
170/**
171  * Returns the font in use for this component.
172  *
173  * @return the font for this component
174  */
175  public Font getFont()
176  {
177    if (font != null)
178      return font;
179
180    if (parent != null)
181      return parent.getFont();
182
183    return null;
184  }
185
186  /**
187   * Sets the font for this component to the specified font.
188   *
189   * @param font the new font for this component
190   */
191  public void setFont(Font font)
192  {
193    this.font = font;
194  }
195
196  /**
197   * Returns the name of this component.
198   *
199   * @return the name of this component
200   */
201  public String getName()
202  {
203    if (name == null && ! nameExplicitlySet)
204      name = generateName();
205    return name;
206  }
207  
208  /**
209   * Subclasses should override this to return unique component names like
210   * "menuitem0".
211   *
212   * @return the generated name for this menu component
213   */
214  String generateName()
215  {
216    // MenuComponent is abstract.
217    return null;
218  }
219
220  /**
221   * Sets the name of this component to the specified name.
222   *
223   * @param name the new name of this component
224   */
225  public void setName(String name)
226  {
227    this.name = name;
228    nameExplicitlySet = true;
229  }
230
231  /**
232   * Returns the parent of this component.
233   * 
234   * @return the parent of this component
235   */
236  public MenuContainer getParent()
237  {
238    return parent;
239  } 
240
241  /**
242   * Sets the parent of this component.
243   *
244   * @param parent the parent to set
245   */
246  final void setParent(MenuContainer parent)
247  {
248    this.parent = parent;
249  }
250
251  /**
252   * Returns the native windowing system peer for this component.
253   *
254   * @return the peer for this component
255   *
256   * @deprecated
257   */
258  public MenuComponentPeer getPeer()
259  {
260    return peer;
261  }
262
263  /**
264   * Sets the peer for this component.
265   *
266   * @param peer the peer to set
267   */
268  final void setPeer(MenuComponentPeer peer)
269  {
270    this.peer = peer;
271  }
272
273  /**
274   * Destroys this component's native peer
275   */
276  public void removeNotify()
277  {
278    if (peer != null)
279      peer.dispose();
280    peer = null;
281  }
282
283  /**
284   * Returns the toolkit in use for this component.
285   *
286   * @return the toolkit for this component
287   */
288  final Toolkit getToolkit()
289  {
290    return toolkit;
291  }
292
293  /**
294   * Returns the object used for synchronization locks on this component
295   * when performing tree and layout functions.
296   *
297   * @return the synchronization lock for this component
298   */
299  protected final Object getTreeLock()
300  {
301    return tree_lock;
302  }
303
304  /**
305   * Sets the sync lock object for this component.
306   *
307   * @param treeLock the sync lock to set
308   */
309  final void setTreeLock(Object treeLock)
310  {
311    this.tree_lock = treeLock;
312  }
313
314  /**
315   * AWT 1.0 event dispatcher.
316   *
317   * @return true if the event was dispatched, false otherwise
318   *
319   * @deprecated Deprecated in favor of <code>dispatchEvent()</code>.
320   */
321  public boolean
322  postEvent(Event event)
323  {
324    boolean retVal = false;
325    MenuContainer parent = getParent();
326    if (parent != null)
327      retVal = parent.postEvent(event);
328
329    return retVal;
330  }
331
332  /**
333   * Sends this event to this component or a subcomponent for processing.
334   *
335   * @param event The event to dispatch
336   */
337  public final void dispatchEvent(AWTEvent event)
338  {
339    // Convert AWT 1.1 event to AWT 1.0 event.
340    Event oldStyleEvent = Component.translateEvent(event);
341    if (oldStyleEvent != null)
342      {
343        postEvent(oldStyleEvent);
344      }
345
346    // See comment in Component.dispatchEvent().
347    dispatchEventImpl(event);
348  }
349
350  /**
351   * Implementation of dispatchEvent. Allows trusted package classes
352   * to dispatch additional events first.  This implementation first
353   * translates <code>event</code> to an AWT 1.0 event and sends the
354   * result to {@link #postEvent}.  The event is then
355   * passed on to {@link #processEvent} for local processing.
356   *
357   * @param event the event to dispatch
358   */
359  void dispatchEventImpl(AWTEvent event)
360  {
361    // Do local processing.
362    processEvent(event);
363  }
364
365  /**
366   * Processes the specified event.  In this class, this method simply
367   * calls one of the more specific event handlers.
368   * 
369   * @param event the event to process
370   */
371  protected void processEvent(AWTEvent event)
372  {
373    // Pass a focus event to the focus listener for
374    // the accessibility context.
375    if (event instanceof FocusEvent)
376      {
377        if (focusListener != null)
378          {
379            switch (event.id)
380            {
381            case FocusEvent.FOCUS_GAINED:
382              focusListener.focusGained((FocusEvent) event);
383              break;
384            case FocusEvent.FOCUS_LOST:
385              focusListener.focusLost((FocusEvent) event);
386              break;
387            }
388          }
389      }
390  }
391
392  /**
393   * Returns a string representation of this component.
394   *
395   * @return a string representation of this component
396   */
397  public String toString()
398  {
399    return getClass().getName() + "[" + paramString() + "]";
400  }
401
402  /**
403   * Returns a debugging string for this component
404   */
405  protected String paramString()
406  {
407    return "name=" + getName();
408  }
409
410  /**
411   * Gets the AccessibleContext associated with this <code>MenuComponent</code>.
412   * As an abstract class, we return null.  Concrete subclasses should return
413   * their implementation of the accessibility context.
414   *
415   * @return null
416   */
417  public AccessibleContext getAccessibleContext()
418  {
419    return null;
420  }
421
422  /**
423   * This class provides a base for the accessibility support of menu
424   * components.
425   *
426   * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
427   */
428  protected abstract class AccessibleAWTMenuComponent
429    extends AccessibleContext
430    implements Serializable, AccessibleComponent, AccessibleSelection
431  {
432
433    /**
434     * Compatible with JDK 1.4.2 revision 5
435     */
436    private static final long serialVersionUID = -4269533416223798698L;
437
438    /**
439     * This is the default constructor.  It should be called by
440     * concrete subclasses to ensure necessary groundwork is completed.
441     */
442    protected AccessibleAWTMenuComponent()
443    {
444      // Nothing to do here.
445    }
446
447    /**
448     * Replaces or supplements the component's selection with the
449     * <code>Accessible</code> child at the supplied index.  If
450     * the component supports multiple selection, the child is
451     * added to the current selection.  Otherwise, the current
452     * selection becomes the specified child.  If the child is
453     * already selected, nothing happens.
454     * <br />
455     * <br />
456     * As the existence of children can not be determined from
457     * this abstract class, the implementation of this method
458     * is left to subclasses.
459     *
460     * @param index the index of the specified child within a
461     *        zero-based list of the component's children
462     */
463    public void addAccessibleSelection(int index)
464    {
465      // Subclasses with children should implement this.
466    }
467
468    /**
469     * Registers the specified focus listener to receive
470     * focus events from this component.
471     *
472     * @param listener the new focus listener
473     */
474    public void addFocusListener(FocusListener listener)
475    {
476       // Chain the new focus listener to the existing chain
477       // of focus listeners.  Each new focus listener is
478       // coupled via multicasting to the existing chain.
479      focusListener = AWTEventMulticaster.add(focusListener, listener);
480    }
481
482    /**
483     * Clears the component's current selection.  Following
484     * the calling of this method, no children of the component
485     * will be selected.
486     * <br />
487     * <br />
488     * As the existence of children can not be determined from
489     * this abstract class, the implementation of this method
490     * is left to subclasses.
491     */
492    public void clearAccessibleSelection()
493    {
494      // Nothing to do here.
495    }
496
497    /**
498     * Returns true if the specified point lies within the
499     * component.  The supplied co-ordinates are assumed to
500     * be relative to the co-ordinate system of the component
501     * itself.  Thus, the point (0,0) is the upper left corner
502     * of this component.
503     * <br />
504     * <br />
505     * Please note that this method depends on a correctly implemented
506     * version of the <code>getBounds()</code> method.  Subclasses
507     * must provide the bounding rectangle via <code>getBounds()</code>
508     * in order for this method to work.  
509     *
510     * @param point the point to check against this component
511     * @return true if the point is within this component
512     * @see #getBounds()
513     */
514    public boolean contains(Point point)
515    {
516      // We can simply return the result of a
517      // test for containment in the bounding rectangle.
518      return getBounds().contains(point);
519    }
520
521    /**
522     * Returns the <code>Accessible</code> child of this component present
523     * at the specified point.  The supplied co-ordinates are
524     * assumed to be relative to the co-ordinate system of this
525     * component (the parent of any returned accessible).  Thus,
526     * the point (0,0) is the upper left corner of this menu
527     * component.
528     * <br />
529     * <br />
530     * As the existence of children can not be determined from
531     * this abstract class, the implementation of this method
532     * is left to subclasses.
533     * 
534     * @param point the point at which the returned accessible
535     *        is located
536     * @return null
537     */
538    public Accessible getAccessibleAt(Point point)
539    {
540      return null;
541    }
542
543    /**
544     * Returns the <code>Accessible</code> child at the supplied
545     * index within the list of children of this component.
546     * <br />
547     * <br />
548     * As the existence of children can not be determined from
549     * this abstract class, the implementation of this method
550     * is left to subclasses.
551     *
552     * @param index the index of the <code>Accessible</code> child
553     *        to retrieve
554     *
555     * @return null
556     */
557    public Accessible getAccessibleChild(int index)
558    {
559      return null;
560    }
561
562    /**
563     * Returns the number of children of this component which
564     * implement the <code>Accessible</code> interface.  If
565     * all children of this component are accessible, then
566     * the returned value will be the same as the number of
567     * children.
568     * <br />
569     * <br />
570     *
571     * @return 0
572     */
573    public int getAccessibleChildrenCount()
574    {
575      return 0;
576    }
577
578    /**
579     * Retrieves the <code>AccessibleComponent</code> associated
580     * with this accessible context and its component.  As the
581     * context itself implements <code>AccessibleComponent</code>,
582     * this is the return value.
583     *
584     * @return the context itself
585     */
586    public AccessibleComponent getAccessibleComponent()
587    {
588      return this;
589    }
590
591    /**
592     * Returns the accessible name for this menu component.  This
593     * is the name given to the component, which may be null if
594     * not set using <code>setName()</code>.
595     * <br />
596     * <br />
597     * The name is not the most appropriate description of this
598     * object.  Subclasses should preferably provide a more
599     * accurate description.  For example, a File menu could
600     * have the description `Lists commands related to the
601     * file system'.
602     *
603     * @return a description of the component.  Currently,
604     *         this is just the contents of the name property
605     *
606     * @see MenuComponent#setName(String)
607     */
608    public String getAccessibleDescription()
609    {
610      return MenuComponent.this.getName();
611    }
612
613    /**
614     * Retrieves the index of this component within its parent.
615     * If no parent exists, -1 is returned.
616     *
617     * @return -1 as the parent, a <code>MenuContainer</code>
618     *         is not <code>Accessible</code>
619     */
620    public int getAccessibleIndexInParent()
621    {
622      return -1;
623    }
624
625    /**
626     * Returns the accessible name of this component.  This
627     * is the name given to the component, which may be null if
628     * not set using <code>setName()</code>.
629     * <br />
630     * <br />
631     * The name property is not the most suitable string to return
632     * for this method.  The string should be localized, and
633     * relevant to the operation of the component.  For example,
634     * it could be the text of a menu item.  However, this can
635     * not be used at this level of abstraction, so it is the
636     * responsibility of subclasses to provide a more appropriate
637     * name.
638     *
639     * @return a localized name for this component.  Currently, this
640     *         is just the contents of the name property
641     *
642     * @see MenuComponent#setName(String)
643     */
644    public String getAccessibleName()
645    {
646      return MenuComponent.this.getName();
647    }
648
649    /**
650     * Returns the <code>Accessible</code> parent of this component.
651     * As the parent of a <code>MenuComponent</code> is a
652     * <code>MenuContainer</code>, which doesn't implement
653     * <code>Accessible</code>, this method returns null.
654     *
655     * @return null
656     */
657    public Accessible getAccessibleParent()
658    {
659      return null;
660    }
661
662    /**
663     * Returns the accessible role of this component.
664     * <br />
665     * <br />
666     * The abstract implementation of this method returns
667     * <code>AccessibleRole.AWT_COMPONENT</code>,
668     * as the abstract component has no specific role.  This
669     * method should be overridden by concrete subclasses, so
670     * as to return an appropriate role for the component.
671     *
672     * @return <code>AccessibleRole.AWT_COMPONENT</code>
673     */
674    public AccessibleRole getAccessibleRole()
675    {
676      return AccessibleRole.AWT_COMPONENT;
677    }
678
679    /**
680     * Retrieves the <code>AccessibleSelection</code> associated
681     * with this accessible context and its component.  As the
682     * context itself implements <code>AccessibleSelection</code>,
683     * this is the return value.
684     *
685     * @return the context itself
686     */
687    public AccessibleSelection getAccessibleSelection()
688    {
689      return this;
690    }
691
692    /**
693     * Retrieves the <code>Accessible</code> selected child
694     * at the specified index.  If there are no selected children
695     * or the index is outside the range of selected children,
696     * null is returned.  Please note that the index refers
697     * to the index of the child in the list of <strong>selected
698     * children</strong>, and not the index of the child in
699     * the list of all <code>Accessible</code> children.
700     * <br />
701     * <br />
702     * As the existence of children can not be determined from
703     * this abstract class, the implementation of this method
704     * is left to subclasses.
705     *
706     * @param index the index of the selected <code>Accessible</code>
707     *        child
708     */
709    public Accessible getAccessibleSelection(int index)
710    {
711      return null;
712    }
713
714    /**
715     * Returns a count of the number of <code>Accessible</code>
716     * children of this component which are currently selected.
717     * If there are no children currently selected, 0 is returned.
718     * <br />
719     * <br />
720     * As the existence of children can not be determined from
721     * this abstract class, the implementation of this method
722     * is left to subclasses.
723     *
724     * @return 0
725     */
726    public int getAccessibleSelectionCount()
727    {
728      return 0;
729    }
730
731    /**
732     * Retrieves the current state of this component
733     * in an accessible form.  For example, a given component
734     * may be visible, selected, disabled, etc.
735     * <br />
736     * <br />
737     * As this class tells us virtually nothing about the component,
738     * except for its name and font, no state information can be
739     * provided.  This implementation thus returns an empty
740     * state set, and it is left to concrete subclasses to provide
741     * a more acceptable and relevant state set.  Changes to these
742     * properties also need to be handled using
743     * <code>PropertyChangeListener</code>s.
744     *
745     * @return an empty <code>AccessibleStateSet</code>
746     */
747    public AccessibleStateSet getAccessibleStateSet()
748    {
749      return new AccessibleStateSet();
750    }
751
752    /**
753     * Returns the background color of the component, or null
754     * if this property is unsupported.
755     * <br />
756     * <br />
757     * This abstract class knows nothing about how the component
758     * is drawn on screen, so this method simply returns the
759     * default system background color used for rendering menus.
760     * Concrete subclasses which handle the drawing of an onscreen
761     * menu component should override this method and provide
762     * the appropriate information.
763     *
764     * @return the default system background color for menus
765     *
766     * @see #setBackground(java.awt.Color)
767     */
768    public Color getBackground()
769    {
770      return SystemColor.menu;
771    }
772
773    /**
774     * Returns a <code>Rectangle</code> which represents the
775     * bounds of this component.  The returned rectangle has the
776     * height and width of the component's bounds, and is positioned
777     * at a location relative to this component's parent, the
778     * <code>MenuContainer</code>.  null is returned if bounds
779     * are not supported by the component.
780     * <br />
781     * <br />
782     * This abstract class knows nothing about how the component
783     * is drawn on screen, so this method simply returns null.
784     * Concrete subclasses which handle the drawing of an onscreen
785     * menu component should override this method and provide
786     * the appropriate information.
787     *
788     * @return null
789     *
790     * @see #setBounds(java.awt.Rectangle)
791     */
792    public Rectangle getBounds()
793    {
794      return null;
795    }
796
797    /**
798     * Returns the <code>Cursor</code> displayed when the pointer
799     * is positioned over this component.  Alternatively, null
800     * is returned if the component doesn't support the cursor
801     * property.
802     * <br />
803     * <br />
804     * This abstract class knows nothing about how the component
805     * is drawn on screen, so this method simply returns the default
806     * system cursor.  Concrete subclasses which handle the drawing
807     * of an onscreen menu component may override this method and provide
808     * the appropriate information.
809     *
810     * @return the default system cursor
811     *
812     * @see #setCursor(java.awt.Cursor)
813     */
814    public Cursor getCursor()
815    {
816      return Cursor.getDefaultCursor();
817    }
818
819    /**
820     * Returns the <code>Font</code> used for text created by this component.
821     *
822     * @return the current font
823     *
824     * @see #setFont(java.awt.Font)
825     */
826    public Font getFont()
827    {
828      return MenuComponent.this.getFont();
829    }
830
831    /**
832     * Retrieves information on the rendering and metrics of the supplied
833     * font.  If font metrics are not supported by this component, null
834     * is returned.
835     * <br />
836     * <br />
837     * The abstract implementation of this method simply uses the toolkit
838     * to obtain the <code>FontMetrics</code>.  Concrete subclasses may
839     * find it more efficient to invoke their peer class directly, if one
840     * is available.
841     *
842     * @param font the font about which to retrieve rendering and metric
843     *        information
844     *
845     * @return the metrics of the given font, as provided by the system
846     *         toolkit
847     *
848     * @throws NullPointerException if the supplied font was null
849     */
850    public FontMetrics getFontMetrics(Font font)
851    {
852      return MenuComponent.this.getToolkit().getFontMetrics(font);
853    }
854
855    /**
856     * Returns the foreground color of the component, or null
857     * if this property is unsupported.
858     * <br />
859     * <br />
860     * This abstract class knows nothing about how the component
861     * is drawn on screen, so this method simply returns the
862     * default system text color used for rendering menus.
863     * Concrete subclasses which handle the drawing of an onscreen
864     * menu component should override this method and provide
865     * the appropriate information.
866     *
867     * @return the default system text color for menus
868     *
869     * @see #setForeground(java.awt.Color)
870     */
871    public Color getForeground()
872    {
873      return SystemColor.menuText;
874    }
875
876    /**
877     * Returns the locale currently in use by this component.
878     * <br />
879     * <br />
880     * This abstract class has no property relating to the
881     * locale used by the component, so this method simply
882     * returns the default locale for the current instance
883     * of the Java Virtual Machine (JVM).  Concrete subclasses
884     * which maintain such a property should override this method
885     * and provide the locale information more accurately.
886     *
887     * @return the default locale for this JVM instance
888     */
889    public Locale getLocale()
890    {
891      return Locale.getDefault();
892    }
893
894    /**
895     * Returns the location of the component, with co-ordinates
896     * relative to the parent component and using the co-ordinate
897     * space of the screen.  Thus, the point (0,0) is the upper
898     * left corner of the parent component.
899     * <br />
900     * <br />
901     * Please note that this method depends on a correctly implemented
902     * version of the <code>getBounds()</code> method.  Subclasses
903     * must provide the bounding rectangle via <code>getBounds()</code>
904     * in order for this method to work.  
905     *
906     * @return the location of the component, relative to its parent
907     *
908     * @see #setLocation(java.awt.Point)
909     */
910    public Point getLocation()
911    {
912      // Simply return the location of the bounding rectangle.
913      return getBounds().getLocation();
914    }
915
916    /**
917     * Returns the location of the component, with co-ordinates
918     * relative to the screen.  Thus, the point (0,0) is the upper
919     * left corner of the screen.  null is returned if the component
920     * is either not on screen or if this property is unsupported.
921     * <br />
922     * <br />
923     * This abstract class knows nothing about how the component
924     * is drawn on screen, so this method simply returns null.
925     * Concrete subclasses which handle the drawing of an onscreen
926     * menu component should override this method and provide
927     * the appropriate information.
928     *
929     * @return the location of the component, relative to the screen
930     */
931    public Point getLocationOnScreen()
932    {
933      return null;
934    }
935
936    /**
937     * Returns the size of the component.
938     * <br />
939     * <br />
940     * Please note that this method depends on a correctly implemented
941     * version of the <code>getBounds()</code> method.  Subclasses
942     * must provide the bounding rectangle via <code>getBounds()</code>
943     * in order for this method to work.  
944     *
945     * @return the size of the component
946     *
947     * @see #setSize(java.awt.Dimension)
948     */
949    public Dimension getSize()
950    {
951      // Simply return the size of the bounding rectangle.
952      return getBounds().getSize();
953    }
954
955    /**
956     * Returns true if the accessible child specified by the supplied index
957     * is currently selected.
958     * <br />
959     * <br />
960     * As the existence of children can not be determined from
961     * this abstract class, the implementation of this method
962     * is left to subclasses.
963     *
964     * @param index the index of the accessible child to check for selection
965     *
966     * @return false
967     */
968    public boolean isAccessibleChildSelected(int index)
969    {
970      return false;
971    }
972
973    /**
974     * Returns true if this component is currently enabled.
975     * <br />
976     * <br />
977     * As this abstract component has no properties related to
978     * its enabled or disabled state, the implementation of this
979     * method is left to subclasses.
980     *
981     * @return false
982     *
983     * @see #setEnabled(boolean)
984     */
985    public boolean isEnabled()
986    {
987      return false;
988    }
989
990    /**
991     * Returns true if this component is included in the traversal
992     * of the current focus from one component to the other.
993     * <br />
994     * <br />
995     * As this abstract component has no properties related to
996     * its ability to accept the focus, the implementation of this
997     * method is left to subclasses.
998     *
999     * @return false
1000     */
1001    public boolean isFocusTraversable()
1002    {
1003      return false;
1004    }
1005
1006    /**
1007     * Returns true if the component is being shown on screen.
1008     * A component is determined to be shown if it is visible,
1009     * and each parent component is also visible.  Please note
1010     * that, even when a component is showing, it may still be
1011     * obscured by other components in front.  This method only
1012     * determines if the component is being drawn on the screen.
1013     * <br />
1014     * <br />
1015     * As this abstract component and its parent have no properties
1016     * relating to visibility, the implementation of this method is
1017     * left to subclasses.
1018     *
1019     * @return false
1020     *
1021     * @see #isVisible()
1022     */
1023    public boolean isShowing()
1024    {
1025      return false;
1026    }
1027
1028    /**
1029     * Returns true if the component is visible.  A component may
1030     * be visible but not drawn on the screen if one of its parent
1031     * components is not visible.  To determine if the component is
1032     * actually drawn on screen, <code>isShowing()</code> should be
1033     * used.
1034     * <br />
1035     * <br />
1036     * As this abstract component has no properties relating to its
1037     * visibility, the implementation of this method is left to subclasses.
1038     *
1039     * @return false
1040     *
1041     * @see #isShowing()
1042     * @see #setVisible(boolean)
1043     */
1044    public boolean isVisible()
1045    {
1046      return false;
1047    }
1048
1049    /**
1050     * Removes the accessible child specified by the supplied index from
1051     * the list of currently selected children.  If the child specified
1052     * is not selected, nothing happens.
1053     * <br />
1054     * <br />
1055     * As the existence of children can not be determined from
1056     * this abstract class, the implementation of this method
1057     * is left to subclasses.
1058     *
1059     * @param index the index of the <code>Accessible</code> child
1060     */
1061    public void removeAccessibleSelection(int index)
1062    {
1063      // Subclasses with children should implement this.
1064    }
1065
1066    /**
1067     * Removes the specified focus listener from the list of registered
1068     * focus listeners for this component.
1069     *
1070     * @param listener the listener to remove
1071     */
1072    public void removeFocusListener(FocusListener listener)
1073    {
1074      // Remove the focus listener from the chain.
1075      focusListener = AWTEventMulticaster.remove(focusListener, listener);
1076    }
1077
1078    /**
1079     * Requests that this component gains focus.  This depends on the
1080     * component being focus traversable.
1081     * <br />
1082     * <br />
1083     * As this abstract component has no properties relating to its
1084     * focus traversability, or access to a peer with request focusing
1085     * abilities, the implementation of this method is left to subclasses.
1086     */
1087    public void requestFocus()
1088    {
1089      // Ignored.
1090    }
1091
1092    /**
1093     * Selects all <code>Accessible</code> children of this component which
1094     * it is possible to select.  The component needs to support multiple
1095     * selections.
1096     * <br />
1097     * <br />
1098     * This abstract component provides a simplistic implementation of this
1099     * method, which ignores the ability of the component to support multiple
1100     * selections and simply uses <code>addAccessibleSelection</code> to
1101     * add each <code>Accessible</code> child to the selection.  The last
1102     * <code>Accessible</code> component is thus selected for components
1103     * which don't support multiple selections.  Concrete implementations should
1104     * override this with a more appopriate and efficient implementation, which
1105     * properly takes into account the ability of the component to support multiple
1106     * selections. 
1107     */
1108    public void selectAllAccessibleSelection()
1109    {
1110      // Simply call addAccessibleSelection() on all accessible children.
1111      for (int a = 0; a < getAccessibleChildrenCount(); ++a)
1112        {
1113          addAccessibleSelection(a);
1114        }
1115    }
1116
1117    /**
1118     * Sets the background color of the component to that specified.
1119     * Unspecified behaviour occurs when null is given as the new
1120     * background color.
1121     * <br />
1122     * <br />
1123     * This abstract class knows nothing about how the component
1124     * is drawn on screen, so this method simply ignores the supplied
1125     * color and continues to use the default system color.   
1126     * Concrete subclasses which handle the drawing of an onscreen
1127     * menu component should override this method and provide
1128     * the appropriate information.
1129     *
1130     * @param color the new color to use for the background
1131     *
1132     * @see #getBackground()
1133     */
1134    public void setBackground(Color color)
1135    {
1136      // Ignored.
1137    }
1138
1139    /**
1140     * Sets the height and width of the component, and its position
1141     * relative to this component's parent, to the values specified
1142     * by the supplied rectangle.  Unspecified behaviour occurs when
1143     * null is given as the new bounds.
1144     * <br />
1145     * <br />
1146     * This abstract class knows nothing about how the component
1147     * is drawn on screen, so this method simply ignores the new
1148     * rectangle and continues to return null from <code>getBounds()</code>.
1149     * Concrete subclasses which handle the drawing of an onscreen
1150     * menu component should override this method and provide
1151     * the appropriate information.
1152     *
1153     * @param rectangle a rectangle which specifies the new bounds of
1154     *        the component
1155     *
1156     * @see #getBounds()
1157     */
1158    public void setBounds(Rectangle rectangle)
1159    {
1160      // Ignored.
1161    }
1162
1163    /**
1164     * Sets the <code>Cursor</code> used when the pointer is positioned over the
1165     * component.  Unspecified behaviour occurs when null is given as the new
1166     * cursor.
1167     * <br />
1168     * <br />
1169     * This abstract class knows nothing about how the component
1170     * is drawn on screen, so this method simply ignores the new cursor
1171     * and continues to return the default system cursor.  Concrete
1172     * subclasses which handle the drawing of an onscreen menu component
1173     * may override this method and provide the appropriate information.
1174     *
1175     * @param cursor the new cursor to use
1176     *
1177     * @see #getCursor()
1178     */
1179    public void setCursor(Cursor cursor)
1180    {
1181      // Ignored.
1182    }
1183
1184    /**
1185     * Sets the enabled/disabled state of this component.
1186     * <br />
1187     * <br />
1188     * As this abstract component has no properties related to
1189     * its enabled or disabled state, the implementation of this
1190     * method is left to subclasses.
1191     *
1192     * @param enabled true if the component should be enabled,
1193     *        false otherwise
1194     *
1195     * @see #isEnabled()
1196     */
1197    public void setEnabled(boolean enabled)
1198    {
1199      // Ignored.
1200    }
1201
1202    /**
1203     * Sets the <code>Font</code> used for text created by this component.
1204     * Unspecified behaviour occurs when null is given as the new
1205     * font.
1206     *
1207     * @param font the new font to use for text.
1208     * @see #getFont()
1209     */
1210    public void setFont(Font font)
1211    {
1212      // Call the method of the enclosing component.
1213      MenuComponent.this.setFont(font);
1214    }
1215
1216    /**
1217     * Sets the foreground color of the component to that specified.
1218     * Unspecified behaviour occurs when null is given as the new
1219     * background color.
1220     * <br />
1221     * <br />
1222     * This abstract class knows nothing about how the component
1223     * is drawn on screen, so this method simply ignores the supplied
1224     * color and continues to return the default system text color used
1225     * for rendering menus.
1226     * Concrete subclasses which handle the drawing of an onscreen
1227     * menu component should override this method and provide
1228     * the appropriate information.
1229     *
1230     * @param color the new foreground color
1231     *
1232     * @see #getForeground()
1233     */
1234    public void setForeground(Color color)
1235    {
1236      // Ignored.
1237    }
1238
1239    /**
1240     * Sets the location of the component, with co-ordinates
1241     * relative to the parent component and using the co-ordinate
1242     * space of the screen.  Thus, the point (0,0) is the upper
1243     * left corner of the parent component.
1244     * <br />
1245     * <br />
1246     * Please note that this method depends on a correctly implemented
1247     * version of the <code>getBounds()</code> method.  Subclasses
1248     * must provide the bounding rectangle via <code>getBounds()</code>
1249     * in order for this method to work.  
1250     *
1251     * @param point the location of the component, relative to its parent
1252     *
1253     * @see #getLocation()
1254     */
1255    public void setLocation(Point point)
1256    {
1257      getBounds().setLocation(point);
1258    }
1259
1260    /**
1261     * Sets the size of the component.
1262     * <br />
1263     * <br />
1264     * Please note that this method depends on a correctly implemented
1265     * version of the <code>getBounds()</code> method.  Subclasses
1266     * must provide the bounding rectangle via <code>getBounds()</code>
1267     * in order for this method to work.  
1268     *
1269     * @param size the new size of the component
1270     *
1271     * @see #getSize()
1272     */
1273    public void setSize(Dimension size)
1274    {
1275      getBounds().setSize(size);
1276    }
1277
1278    /**
1279     * Sets the visibility state of the component.  A component may
1280     * be visible but not drawn on the screen if one of its parent
1281     * components is not visible.  To determine if the component is
1282     * actually drawn on screen, <code>isShowing()</code> should be
1283     * used.
1284     * <br />
1285     * <br />
1286     * As this abstract component has no properties relating to its
1287     * visibility, the implementation of this method is left to subclasses.
1288     *
1289     * @param visibility the new visibility of the component -- true if
1290     *        the component is visible, false if not
1291     *
1292     * @see #isShowing()
1293     * @see #isVisible()
1294     */
1295    public void setVisible(boolean visibility)
1296    {
1297      // Ignored.
1298    }
1299
1300  }
1301
1302}