/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

package javax.accessibility;

import sun.awt.AWTAccessor;
import sun.awt.AppContext;

import java.util.Locale;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.beans.PropertyChangeEvent;
import java.awt.IllegalComponentStateException;

/**
 * AccessibleContext represents the minimum information all accessible objects
 * return.  This information includes the accessible name, description, role,
 * and state of the object, as well as information about its parent and
 * children.  AccessibleContext also contains methods for
 * obtaining more specific accessibility information about a component.
 * If the component supports them, these methods will return an object that
 * implements one or more of the following interfaces:
 * <P><ul>
 * <li>{@link AccessibleAction} - the object can perform one or more actions.
 * This interface provides the standard mechanism for an assistive
 * technology to determine what those actions are and tell the object
 * to perform them.  Any object that can be manipulated should
 * support this interface.
 * <li>{@link AccessibleComponent} - the object has a graphical representation.
 * This interface provides the standard mechanism for an assistive
 * technology to determine and set the graphical representation of the
 * object.  Any object that is rendered on the screen should support
 * this interface.
 * <li>{@link  AccessibleSelection} - the object allows its children to be
 * selected.  This interface provides the standard mechanism for an
 * assistive technology to determine the currently selected children of the object
 * as well as modify its selection set.  Any object that has children
 * that can be selected should support this interface.
 * <li>{@link AccessibleText} - the object presents editable textual information
 * on the display.  This interface provides the standard mechanism for
 * an assistive technology to access that text via its content, attributes,
 * and spatial location.  Any object that contains editable text should
 * support this interface.
 * <li>{@link AccessibleValue} - the object supports a numerical value.  This
 * interface provides the standard mechanism for an assistive technology
 * to determine and set the current value of the object, as well as obtain its
 * minimum and maximum values.  Any object that supports a numerical value
 * should support this interface.</ul>
 *
 *
 * @beaninfo
 *   attribute: isContainer false
 * description: Minimal information that all accessible objects return
 *

 * @author      Peter Korn
 * @author      Hans Muller
 * @author      Willie Walker
 * @author      Lynn Monsanto
 */
public abstract class AccessibleContext {

    /**
     * The AppContext that should be used to dispatch events for this
     * AccessibleContext
     */
    private volatile AppContext targetAppContext;

    static {
        AWTAccessor.setAccessibleContextAccessor(new AWTAccessor.AccessibleContextAccessor() {
            @Override
            public void setAppContext(AccessibleContext accessibleContext, AppContext appContext) {
                accessibleContext.targetAppContext = appContext;
            }

            @Override
            public AppContext getAppContext(AccessibleContext accessibleContext) {
                return accessibleContext.targetAppContext;
            }
        });
    }

   /**
    * Constant used to determine when the accessibleName property has
    * changed.  The old value in the PropertyChangeEvent will be the old
    * accessibleName and the new value will be the new accessibleName.
    *
    * @see #getAccessibleName
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_NAME_PROPERTY = "AccessibleName";

   /**
    * Constant used to determine when the accessibleDescription property has
    * changed.  The old value in the PropertyChangeEvent will be the
    * old accessibleDescription and the new value will be the new
    * accessibleDescription.
    *
    * @see #getAccessibleDescription
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_DESCRIPTION_PROPERTY = "AccessibleDescription";

   /**
    * Constant used to determine when the accessibleStateSet property has
    * changed.  The old value will be the old AccessibleState and the new
    * value will be the new AccessibleState in the accessibleStateSet.
    * For example, if a component that supports the vertical and horizontal
    * states changes its orientation from vertical to horizontal, the old
    * value will be AccessibleState.VERTICAL and the new value will be
    * AccessibleState.HORIZONTAL.  Please note that either value can also
    * be null.  For example, when a component changes from being enabled
    * to disabled, the old value will be AccessibleState.ENABLED
    * and the new value will be null.
    *
    * @see #getAccessibleStateSet
    * @see AccessibleState
    * @see AccessibleStateSet
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_STATE_PROPERTY = "AccessibleState";

   /**
    * Constant used to determine when the accessibleValue property has
    * changed.  The old value in the PropertyChangeEvent will be a Number
    * representing the old value and the new value will be a Number
    * representing the new value
    *
    * @see #getAccessibleValue
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_VALUE_PROPERTY = "AccessibleValue";

   /**
    * Constant used to determine when the accessibleSelection has changed.
    * The old and new values in the PropertyChangeEvent are currently
    * reserved for future use.
    *
    * @see #getAccessibleSelection
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_SELECTION_PROPERTY = "AccessibleSelection";

   /**
    * Constant used to determine when the accessibleText caret has changed.
    * The old value in the PropertyChangeEvent will be an
    * integer representing the old caret position, and the new value will
    * be an integer representing the new/current caret position.
    *
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_CARET_PROPERTY = "AccessibleCaret";

   /**
    * Constant used to determine when the visual appearance of the object
    * has changed.  The old and new values in the PropertyChangeEvent are
    * currently reserved for future use.
    *
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_VISIBLE_DATA_PROPERTY = "AccessibleVisibleData";

   /**
    * Constant used to determine when Accessible children are added/removed
    * from the object.  If an Accessible child is being added, the old
    * value will be null and the new value will be the Accessible child.  If an
    * Accessible child is being removed, the old value will be the Accessible
    * child, and the new value will be null.
    *
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_CHILD_PROPERTY = "AccessibleChild";

   /**
    * Constant used to determine when the active descendant of a component
    * has changed.  The active descendant is used for objects such as
    * list, tree, and table, which may have transient children.  When the
    * active descendant has changed, the old value of the property change
    * event will be the Accessible representing the previous active child, and
    * the new value will be the Accessible representing the current active
    * child.
    *
    * @see #addPropertyChangeListener
    */
   public static final String ACCESSIBLE_ACTIVE_DESCENDANT_PROPERTY = "AccessibleActiveDescendant";

    /**
     * Constant used to indicate that the table caption has changed
     * The old value in the PropertyChangeEvent will be an Accessible
     * representing the previous table caption and the new value will
     * be an Accessible representing the new table caption.
     * @see Accessible
     * @see AccessibleTable
     */
    public static final String ACCESSIBLE_TABLE_CAPTION_CHANGED =
        "accessibleTableCaptionChanged";

    /**
     * Constant used to indicate that the table summary has changed
     * The old value in the PropertyChangeEvent will be an Accessible
     * representing the previous table summary and the new value will
     * be an Accessible representing the new table summary.
     * @see Accessible
     * @see AccessibleTable
     */
    public static final String ACCESSIBLE_TABLE_SUMMARY_CHANGED =
        "accessibleTableSummaryChanged";

    /**
     * Constant used to indicate that table data has changed.
     * The old value in the PropertyChangeEvent will be null and the
     * new value will be an AccessibleTableModelChange representing
     * the table change.
     * @see AccessibleTable
     * @see AccessibleTableModelChange
     */
    public static final String ACCESSIBLE_TABLE_MODEL_CHANGED =
        "accessibleTableModelChanged";

    /**
     * Constant used to indicate that the row header has changed
     * The old value in the PropertyChangeEvent will be null and the
     * new value will be an AccessibleTableModelChange representing
     * the header change.
     * @see AccessibleTable
     * @see AccessibleTableModelChange
     */
    public static final String ACCESSIBLE_TABLE_ROW_HEADER_CHANGED =
        "accessibleTableRowHeaderChanged";

    /**
     * Constant used to indicate that the row description has changed
     * The old value in the PropertyChangeEvent will be null and the
     * new value will be an Integer representing the row index.
     * @see AccessibleTable
     */
    public static final String ACCESSIBLE_TABLE_ROW_DESCRIPTION_CHANGED =
        "accessibleTableRowDescriptionChanged";

    /**
     * Constant used to indicate that the column header has changed
     * The old value in the PropertyChangeEvent will be null and the
     * new value will be an AccessibleTableModelChange representing
     * the header change.
     * @see AccessibleTable
     * @see AccessibleTableModelChange
     */
    public static final String ACCESSIBLE_TABLE_COLUMN_HEADER_CHANGED =
        "accessibleTableColumnHeaderChanged";

    /**
     * Constant used to indicate that the column description has changed
     * The old value in the PropertyChangeEvent will be null and the
     * new value will be an Integer representing the column index.
     * @see AccessibleTable
     */
    public static final String ACCESSIBLE_TABLE_COLUMN_DESCRIPTION_CHANGED =
        "accessibleTableColumnDescriptionChanged";

    /**
     * Constant used to indicate that the supported set of actions
     * has changed.  The old value in the PropertyChangeEvent will
     * be an Integer representing the old number of actions supported
     * and the new value will be an Integer representing the new
     * number of actions supported.
     * @see AccessibleAction
     */
    public static final String ACCESSIBLE_ACTION_PROPERTY =
        "accessibleActionProperty";

    /**
     * Constant used to indicate that a hypertext element has received focus.
     * The old value in the PropertyChangeEvent will be an Integer
     * representing the start index in the document of the previous element
     * that had focus and the new value will be an Integer representing
     * the start index in the document of the current element that has
     * focus.  A value of -1 indicates that an element does not or did
     * not have focus.
     * @see AccessibleHyperlink
     */
    public static final String ACCESSIBLE_HYPERTEXT_OFFSET =
        "AccessibleHypertextOffset";

    /**
     * PropertyChangeEvent which indicates that text has changed.
     * <br>
     * For text insertion, the oldValue is null and the newValue
     * is an AccessibleTextSequence specifying the text that was
     * inserted.
     * <br>
     * For text deletion, the oldValue is an AccessibleTextSequence
     * specifying the text that was deleted and the newValue is null.
     * <br>
     * For text replacement, the oldValue is an AccessibleTextSequence
     * specifying the old text and the newValue is an AccessibleTextSequence
     * specifying the new text.
     *
     * @see #getAccessibleText
     * @see #addPropertyChangeListener
     * @see AccessibleTextSequence
     */
    public static final String ACCESSIBLE_TEXT_PROPERTY
        = "AccessibleText";

    /**
     * PropertyChangeEvent which indicates that a significant change
     * has occurred to the children of a component like a tree or text.
     * This change notifies the event listener that it needs to
     * reacquire the state of the subcomponents. The oldValue is
     * null and the newValue is the component whose children have
     * become invalid.
     *
     * @see #getAccessibleText
     * @see #addPropertyChangeListener
     * @see AccessibleTextSequence
     *
     * @since 1.5
     */
    public static final String ACCESSIBLE_INVALIDATE_CHILDREN =
        "accessibleInvalidateChildren";

     /**
     * PropertyChangeEvent which indicates that text attributes have changed.
     * <br>
     * For attribute insertion, the oldValue is null and the newValue
     * is an AccessibleAttributeSequence specifying the attributes that were
     * inserted.
     * <br>
     * For attribute deletion, the oldValue is an AccessibleAttributeSequence
     * specifying the attributes that were deleted and the newValue is null.
     * <br>
     * For attribute replacement, the oldValue is an AccessibleAttributeSequence
     * specifying the old attributes and the newValue is an
     * AccessibleAttributeSequence specifying the new attributes.
     *
     * @see #getAccessibleText
     * @see #addPropertyChangeListener
     * @see AccessibleAttributeSequence
     *
     * @since 1.5
     */
    public static final String ACCESSIBLE_TEXT_ATTRIBUTES_CHANGED =
        "accessibleTextAttributesChanged";

   /**
     * PropertyChangeEvent which indicates that a change has occurred
     * in a component's bounds.
     * The oldValue is the old component bounds and the newValue is
     * the new component bounds.
     *
     * @see #addPropertyChangeListener
     *
     * @since 1.5
     */
    public static final String ACCESSIBLE_COMPONENT_BOUNDS_CHANGED =
        "accessibleComponentBoundsChanged";

    /**
     * The accessible parent of this object.
     *
     * @see #getAccessibleParent
     * @see #setAccessibleParent
     */
    protected Accessible accessibleParent = null;

    /**
     * A localized String containing the name of the object.
     *
     * @see #getAccessibleName
     * @see #setAccessibleName
     */
    protected String accessibleName = null;

    /**
     * A localized String containing the description of the object.
     *
     * @see #getAccessibleDescription
     * @see #setAccessibleDescription
     */
    protected String accessibleDescription = null;

    /**
     * Used to handle the listener list for property change events.
     *
     * @see #addPropertyChangeListener
     * @see #removePropertyChangeListener
     * @see #firePropertyChangeListener
     */
    private PropertyChangeSupport accessibleChangeSupport = null;

    /**
     * Used to represent the context's relation set
     * @see #getAccessibleRelationSet
     */
    private AccessibleRelationSet relationSet
        = new AccessibleRelationSet();

    private Object nativeAXResource;

    /**
     * Gets the accessibleName property of this object.  The accessibleName
     * property of an object is a localized String that designates the purpose
     * of the object.  For example, the accessibleName property of a label
     * or button might be the text of the label or button itself.  In the
     * case of an object that doesn't display its name, the accessibleName
     * should still be set.  For example, in the case of a text field used
     * to enter the name of a city, the accessibleName for the en_US locale
     * could be 'city.'
     *
     * @return the localized name of the object; null if this
     * object does not have a name
     *
     * @see #setAccessibleName
     */
    public String getAccessibleName() {
        return accessibleName;
    }

    /**
     * Sets the localized accessible name of this object.  Changing the
     * name will cause a PropertyChangeEvent to be fired for the
     * ACCESSIBLE_NAME_PROPERTY property.
     *
     * @param s the new localized name of the object.
     *
     * @see #getAccessibleName
     * @see #addPropertyChangeListener
     *
     * @beaninfo
     *    preferred:   true
     *    description: Sets the accessible name for the component.
     */
    public void setAccessibleName(String s) {
        String oldName = accessibleName;
        accessibleName = s;
        firePropertyChange(ACCESSIBLE_NAME_PROPERTY,oldName,accessibleName);
    }

    /**
     * Gets the accessibleDescription property of this object.  The
     * accessibleDescription property of this object is a short localized
     * phrase describing the purpose of the object.  For example, in the
     * case of a 'Cancel' button, the accessibleDescription could be
     * 'Ignore changes and close dialog box.'
     *
     * @return the localized description of the object; null if
     * this object does not have a description
     *
     * @see #setAccessibleDescription
     */
    public String getAccessibleDescription() {
        return accessibleDescription;
    }

    /**
     * Sets the accessible description of this object.  Changing the
     * name will cause a PropertyChangeEvent to be fired for the
     * ACCESSIBLE_DESCRIPTION_PROPERTY property.
     *
     * @param s the new localized description of the object
     *
     * @see #setAccessibleName
     * @see #addPropertyChangeListener
     *
     * @beaninfo
     *    preferred:   true
     *    description: Sets the accessible description for the component.
     */
    public void setAccessibleDescription(String s) {
        String oldDescription = accessibleDescription;
        accessibleDescription = s;
        firePropertyChange(ACCESSIBLE_DESCRIPTION_PROPERTY,
                           oldDescription,accessibleDescription);
    }

    /**
     * Gets the role of this object.  The role of the object is the generic
     * purpose or use of the class of this object.  For example, the role
     * of a push button is AccessibleRole.PUSH_BUTTON.  The roles in
     * AccessibleRole are provided so component developers can pick from
     * a set of predefined roles.  This enables assistive technologies to
     * provide a consistent interface to various tweaked subclasses of
     * components (e.g., use AccessibleRole.PUSH_BUTTON for all components
     * that act like a push button) as well as distinguish between subclasses
     * that behave differently (e.g., AccessibleRole.CHECK_BOX for check boxes
     * and AccessibleRole.RADIO_BUTTON for radio buttons).
     * <p>Note that the AccessibleRole class is also extensible, so
     * custom component developers can define their own AccessibleRole's
     * if the set of predefined roles is inadequate.
     *
     * @return an instance of AccessibleRole describing the role of the object
     * @see AccessibleRole
     */
    public abstract AccessibleRole getAccessibleRole();

    /**
     * Gets the state set of this object.  The AccessibleStateSet of an object
     * is composed of a set of unique AccessibleStates.  A change in the
     * AccessibleStateSet of an object will cause a PropertyChangeEvent to
     * be fired for the ACCESSIBLE_STATE_PROPERTY property.
     *
     * @return an instance of AccessibleStateSet containing the
     * current state set of the object
     * @see AccessibleStateSet
     * @see AccessibleState
     * @see #addPropertyChangeListener
     */
    public abstract AccessibleStateSet getAccessibleStateSet();

    /**
     * Gets the Accessible parent of this object.
     *
     * @return the Accessible parent of this object; null if this
     * object does not have an Accessible parent
     */
    public Accessible getAccessibleParent() {
        return accessibleParent;
    }

    /**
     * Sets the Accessible parent of this object.  This is meant to be used
     * only in the situations where the actual component's parent should
     * not be treated as the component's accessible parent and is a method
     * that should only be called by the parent of the accessible child.
     *
     * @param a - Accessible to be set as the parent
     */
    public void setAccessibleParent(Accessible a) {
        accessibleParent = a;
    }

    /**
     * Gets the 0-based index of this object in its accessible parent.
     *
     * @return the 0-based index of this object in its parent; -1 if this
     * object does not have an accessible parent.
     *
     * @see #getAccessibleParent
     * @see #getAccessibleChildrenCount
     * @see #getAccessibleChild
     */
    public abstract int getAccessibleIndexInParent();

    /**
     * Returns the number of accessible children of the object.
     *
     * @return the number of accessible children of the object.
     */
    public abstract int getAccessibleChildrenCount();

    /**
     * Returns the specified Accessible child of the object.  The Accessible
     * children of an Accessible object are zero-based, so the first child
     * of an Accessible child is at index 0, the second child is at index 1,
     * and so on.
     *
     * @param i zero-based index of child
     * @return the Accessible child of the object
     * @see #getAccessibleChildrenCount
     */
    public abstract Accessible getAccessibleChild(int i);

    /**
     * Gets the locale of the component. If the component does not have a
     * locale, then the locale of its parent is returned.
     *
     * @return this component's locale.  If this component does not have
     * a locale, the locale of its parent is returned.
     *
     * @exception IllegalComponentStateException
     * If the Component does not have its own locale and has not yet been
     * added to a containment hierarchy such that the locale can be
     * determined from the containing parent.
     */
    public abstract Locale getLocale() throws IllegalComponentStateException;

    /**
     * Adds a PropertyChangeListener to the listener list.
     * The listener is registered for all Accessible properties and will
     * be called when those properties change.
     *
     * @see #ACCESSIBLE_NAME_PROPERTY
     * @see #ACCESSIBLE_DESCRIPTION_PROPERTY
     * @see #ACCESSIBLE_STATE_PROPERTY
     * @see #ACCESSIBLE_VALUE_PROPERTY
     * @see #ACCESSIBLE_SELECTION_PROPERTY
     * @see #ACCESSIBLE_TEXT_PROPERTY
     * @see #ACCESSIBLE_VISIBLE_DATA_PROPERTY
     *
     * @param listener  The PropertyChangeListener to be added
     */
    public void addPropertyChangeListener(PropertyChangeListener listener) {
        if (accessibleChangeSupport == null) {
            accessibleChangeSupport = new PropertyChangeSupport(this);
        }
        accessibleChangeSupport.addPropertyChangeListener(listener);
    }

    /**
     * Removes a PropertyChangeListener from the listener list.
     * This removes a PropertyChangeListener that was registered
     * for all properties.
     *
     * @param listener  The PropertyChangeListener to be removed
     */
    public void removePropertyChangeListener(PropertyChangeListener listener) {
        if (accessibleChangeSupport != null) {
            accessibleChangeSupport.removePropertyChangeListener(listener);
        }
    }

    /**
     * Gets the AccessibleAction associated with this object that supports
     * one or more actions.
     *
     * @return AccessibleAction if supported by object; else return null
     * @see AccessibleAction
     */
    public AccessibleAction getAccessibleAction() {
        return null;
    }

    /**
     * Gets the AccessibleComponent associated with this object that has a
     * graphical representation.
     *
     * @return AccessibleComponent if supported by object; else return null
     * @see AccessibleComponent
     */
    public AccessibleComponent getAccessibleComponent() {
        return null;
    }

    /**
     * Gets the AccessibleSelection associated with this object which allows its
     * Accessible children to be selected.
     *
     * @return AccessibleSelection if supported by object; else return null
     * @see AccessibleSelection
     */
    public AccessibleSelection getAccessibleSelection() {
        return null;
    }

    /**
     * Gets the AccessibleText associated with this object presenting
     * text on the display.
     *
     * @return AccessibleText if supported by object; else return null
     * @see AccessibleText
     */
    public AccessibleText getAccessibleText() {
        return null;
    }

    /**
     * Gets the AccessibleEditableText associated with this object
     * presenting editable text on the display.
     *
     * @return AccessibleEditableText if supported by object; else return null
     * @see AccessibleEditableText
     * @since 1.4
     */
    public AccessibleEditableText getAccessibleEditableText() {
        return null;
    }


    /**
     * Gets the AccessibleValue associated with this object that supports a
     * Numerical value.
     *
     * @return AccessibleValue if supported by object; else return null
     * @see AccessibleValue
     */
    public AccessibleValue getAccessibleValue() {
        return null;
    }

    /**
     * Gets the AccessibleIcons associated with an object that has
     * one or more associated icons
     *
     * @return an array of AccessibleIcon if supported by object;
     * otherwise return null
     * @see AccessibleIcon
     * @since 1.3
     */
    public AccessibleIcon [] getAccessibleIcon() {
        return null;
    }

    /**
     * Gets the AccessibleRelationSet associated with an object
     *
     * @return an AccessibleRelationSet if supported by object;
     * otherwise return null
     * @see AccessibleRelationSet
     * @since 1.3
     */
    public AccessibleRelationSet getAccessibleRelationSet() {
        return relationSet;
    }

    /**
     * Gets the AccessibleTable associated with an object
     *
     * @return an AccessibleTable if supported by object;
     * otherwise return null
     * @see AccessibleTable
     * @since 1.3
     */
    public AccessibleTable getAccessibleTable() {
        return null;
    }

    /**
     * Support for reporting bound property changes.  If oldValue and
     * newValue are not equal and the PropertyChangeEvent listener list
     * is not empty, then fire a PropertyChange event to each listener.
     * In general, this is for use by the Accessible objects themselves
     * and should not be called by an application program.
     * @param propertyName  The programmatic name of the property that
     * was changed.
     * @param oldValue  The old value of the property.
     * @param newValue  The new value of the property.
     * @see java.beans.PropertyChangeSupport
     * @see #addPropertyChangeListener
     * @see #removePropertyChangeListener
     * @see #ACCESSIBLE_NAME_PROPERTY
     * @see #ACCESSIBLE_DESCRIPTION_PROPERTY
     * @see #ACCESSIBLE_STATE_PROPERTY
     * @see #ACCESSIBLE_VALUE_PROPERTY
     * @see #ACCESSIBLE_SELECTION_PROPERTY
     * @see #ACCESSIBLE_TEXT_PROPERTY
     * @see #ACCESSIBLE_VISIBLE_DATA_PROPERTY
     */
    public void firePropertyChange(String propertyName,
                                   Object oldValue,
                                   Object newValue) {
        if (accessibleChangeSupport != null) {
            if (newValue instanceof PropertyChangeEvent) {
                PropertyChangeEvent pce = (PropertyChangeEvent)newValue;
                accessibleChangeSupport.firePropertyChange(pce);
            } else {
                accessibleChangeSupport.firePropertyChange(propertyName,
                                                           oldValue,
                                                           newValue);
            }
        }
    }
}
