Java example source code file (JScrollPane.java)

This example Java source code file (JScrollPane.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

awt, bean, border, component, gui, horizontal_scrollbar_as_needed, javabean, jscrollbar, jscrollpane, jviewport, lower_left_corner, lower_right_corner, rectangle, scrollable, string, swing, transient, upper_left_corner, upper_right_corner, vertical_scrollbar_as_needed

The JScrollPane.java Java example source code

/*
 * 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.swing;

import javax.swing.plaf.*;
import javax.swing.border.*;
import javax.swing.event.*;
import javax.accessibility.*;

import java.awt.Component;
import java.awt.ComponentOrientation;
import java.awt.Rectangle;
import java.awt.Insets;
import java.awt.LayoutManager;
import java.awt.Point;

import java.io.ObjectOutputStream;
import java.io.IOException;

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.Transient;

/**
 * Provides a scrollable view of a lightweight component.
 * A <code>JScrollPane manages a viewport, optional
 * vertical and horizontal scroll bars, and optional row and
 * column heading viewports.
 * You can find task-oriented documentation of <code>JScrollPane in
 *  <a href="http://docs.oracle.com/javase/tutorial/uiswing/components/scrollpane.html">How to Use Scroll Panes,
 * a section in <em>The Java Tutorial.  Note that
 * <code>JScrollPane does not support heavyweight components.
 *
 * <TABLE STYLE="FLOAT:RIGHT" BORDER="0" SUMMARY="layout">
 *    <TR>
 *    <TD ALIGN="CENTER">
 *      <P STYLE="TEXT-ALIGN:CENTER"> provides a window,
 * or "viewport" onto a data
 * source -- for example, a text file. That data source is the
 * "scrollable client" (aka data model) displayed by the
 * <code>JViewport view.
 * A <code>JScrollPane basically consists of JScrollBars,
 * a <code>JViewport, and the wiring between them,
 * as shown in the diagram at right.
 * <p>
 * In addition to the scroll bars and viewport,
 * a <code>JScrollPane can have a
 * column header and a row header. Each of these is a
 * <code>JViewport object that
 * you specify with <code>setRowHeaderView,
 * and <code>setColumnHeaderView.
 * The column header viewport automatically scrolls left and right, tracking
 * the left-right scrolling of the main viewport.
 * (It never scrolls vertically, however.)
 * The row header acts in a similar fashion.
 * <p>
 * Where two scroll bars meet, the row header meets the column header,
 * or a scroll bar meets one of the headers, both components stop short
 * of the corner, leaving a rectangular space which is, by default, empty.
 * These spaces can potentially exist in any number of the four corners.
 * In the previous diagram, the top right space is present and identified
 * by the label "corner component".
 * <p>
 * Any number of these empty spaces can be replaced by using the
 * <code>setCorner method to add a component to a particular corner.
 * (Note: The same component cannot be added to multiple corners.)
 * This is useful if there's
 * some extra decoration or function you'd like to add to the scroll pane.
 * The size of each corner component is entirely determined by the size of the
 * headers and/or scroll bars that surround it.
 * <p>
 * A corner component will only be visible if there is an empty space in that
 * corner for it to exist in. For example, consider a component set into the
 * top right corner of a scroll pane with a column header. If the scroll pane's
 * vertical scrollbar is not present, perhaps because the view component hasn't
 * grown large enough to require it, then the corner component will not be
 * shown (since there is no empty space in that corner created by the meeting
 * of the header and vertical scroll bar). Forcing the scroll bar to always be
 * shown, using
 * <code>setVerticalScrollBarPolicy(VERTICAL_SCROLLBAR_ALWAYS),
 * will ensure that the space for the corner component always exists.
 * <p>
 * To add a border around the main viewport,
 * you can use <code>setViewportBorder.
 * (Of course, you can also add a border around the whole scroll pane using
 * <code>setBorder.)
 * <p>
 * A common operation to want to do is to set the background color that will
 * be used if the main viewport view is smaller than the viewport, or is
 * not opaque. This can be accomplished by setting the background color
 * of the viewport, via <code>scrollPane.getViewport().setBackground().
 * The reason for setting the color of the viewport and not the scrollpane
 * is that by default <code>JViewport is opaque
 * which, among other things, means it will completely fill
 * in its background using its background color.  Therefore when
 * <code>JScrollPane draws its background the viewport will
 * usually draw over it.
 * <p>
 * By default <code>JScrollPane uses ScrollPaneLayout
 * to handle the layout of its child Components. <code>ScrollPaneLayout
 * determines the size to make the viewport view in one of two ways:
 * <ol>
 *   <li>If the view implements Scrollable
 *       a combination of <code>getPreferredScrollableViewportSize,
 *       <code>getScrollableTracksViewportWidth and
 *       <code>getScrollableTracksViewportHeightis used, otherwise
 *   <li>getPreferredSize is used.
 * </ol>
 * <p>
 * <strong>Warning: Swing is not thread safe. For more
 * information see <a
 * href="package-summary.html#threading">Swing's Threading
 * Policy</a>.
 * <p>
 * <strong>Warning:
 * Serialized objects of this class will not be compatible with
 * future Swing releases. The current serialization support is
 * appropriate for short term storage or RMI between applications running
 * the same version of Swing.  As of 1.4, support for long term storage
 * of all JavaBeans™
 * has been added to the <code>java.beans package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @see JScrollBar
 * @see JViewport
 * @see ScrollPaneLayout
 * @see Scrollable
 * @see Component#getPreferredSize
 * @see #setViewportView
 * @see #setRowHeaderView
 * @see #setColumnHeaderView
 * @see #setCorner
 * @see #setViewportBorder
 *
 * @beaninfo
 *     attribute: isContainer true
 *     attribute: containerDelegate getViewport
 *   description: A specialized container that manages a viewport, optional scrollbars and headers
 *
 * @author Hans Muller
 */
public class JScrollPane extends JComponent implements ScrollPaneConstants, Accessible
{
    private Border viewportBorder;

    /**
     * @see #getUIClassID
     * @see #readObject
     */
    private static final String uiClassID = "ScrollPaneUI";

    /**
     * The display policy for the vertical scrollbar.
     * The default is
     * <code>ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED.
     * @see #setVerticalScrollBarPolicy
     */
    protected int verticalScrollBarPolicy = VERTICAL_SCROLLBAR_AS_NEEDED;


    /**
     * The display policy for the horizontal scrollbar.
     * The default is
     * <code>ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED.
     * @see #setHorizontalScrollBarPolicy
     */
    protected int horizontalScrollBarPolicy = HORIZONTAL_SCROLLBAR_AS_NEEDED;


    /**
     * The scrollpane's viewport child.  Default is an empty
     * <code>JViewport.
     * @see #setViewport
     */
    protected JViewport viewport;


    /**
     * The scrollpane's vertical scrollbar child.
     * Default is a <code>JScrollBar.
     * @see #setVerticalScrollBar
     */
    protected JScrollBar verticalScrollBar;


    /**
     * The scrollpane's horizontal scrollbar child.
     * Default is a <code>JScrollBar.
     * @see #setHorizontalScrollBar
     */
    protected JScrollBar horizontalScrollBar;


    /**
     * The row header child.  Default is <code>null.
     * @see #setRowHeader
     */
    protected JViewport rowHeader;


    /**
     * The column header child.  Default is <code>null.
     * @see #setColumnHeader
     */
    protected JViewport columnHeader;


    /**
     * The component to display in the lower left corner.
     * Default is <code>null.
     * @see #setCorner
     */
    protected Component lowerLeft;


    /**
     * The component to display in the lower right corner.
     * Default is <code>null.
     * @see #setCorner
     */
    protected Component lowerRight;


    /**
     * The component to display in the upper left corner.
     * Default is <code>null.
     * @see #setCorner
     */
    protected Component upperLeft;


    /**
     * The component to display in the upper right corner.
     * Default is <code>null.
     * @see #setCorner
     */
    protected Component upperRight;

    /*
     * State flag for mouse wheel scrolling
     */
    private boolean wheelScrollState = true;

    /**
     * Creates a <code>JScrollPane that displays the view
     * component in a viewport
     * whose view position can be controlled with a pair of scrollbars.
     * The scrollbar policies specify when the scrollbars are displayed,
     * For example, if <code>vsbPolicy is
     * <code>VERTICAL_SCROLLBAR_AS_NEEDED
     * then the vertical scrollbar only appears if the view doesn't fit
     * vertically. The available policy settings are listed at
     * {@link #setVerticalScrollBarPolicy} and
     * {@link #setHorizontalScrollBarPolicy}.
     *
     * @see #setViewportView
     *
     * @param view the component to display in the scrollpanes viewport
     * @param vsbPolicy an integer that specifies the vertical
     *          scrollbar policy
     * @param hsbPolicy an integer that specifies the horizontal
     *          scrollbar policy
     */
    public JScrollPane(Component view, int vsbPolicy, int hsbPolicy)
    {
        setLayout(new ScrollPaneLayout.UIResource());
        setVerticalScrollBarPolicy(vsbPolicy);
        setHorizontalScrollBarPolicy(hsbPolicy);
        setViewport(createViewport());
        setVerticalScrollBar(createVerticalScrollBar());
        setHorizontalScrollBar(createHorizontalScrollBar());
        if (view != null) {
            setViewportView(view);
        }
        setUIProperty("opaque",true);
        updateUI();

        if (!this.getComponentOrientation().isLeftToRight()) {
            viewport.setViewPosition(new Point(Integer.MAX_VALUE, 0));
        }
    }


    /**
     * Creates a <code>JScrollPane that displays the
     * contents of the specified
     * component, where both horizontal and vertical scrollbars appear
     * whenever the component's contents are larger than the view.
     *
     * @see #setViewportView
     * @param view the component to display in the scrollpane's viewport
     */
    public JScrollPane(Component view) {
        this(view, VERTICAL_SCROLLBAR_AS_NEEDED, HORIZONTAL_SCROLLBAR_AS_NEEDED);
    }


    /**
     * Creates an empty (no viewport view) <code>JScrollPane
     * with specified
     * scrollbar policies. The available policy settings are listed at
     * {@link #setVerticalScrollBarPolicy} and
     * {@link #setHorizontalScrollBarPolicy}.
     *
     * @see #setViewportView
     *
     * @param vsbPolicy an integer that specifies the vertical
     *          scrollbar policy
     * @param hsbPolicy an integer that specifies the horizontal
     *          scrollbar policy
     */
    public JScrollPane(int vsbPolicy, int hsbPolicy) {
        this(null, vsbPolicy, hsbPolicy);
    }


    /**
     * Creates an empty (no viewport view) <code>JScrollPane
     * where both horizontal and vertical scrollbars appear when needed.
     */
    public JScrollPane() {
        this(null, VERTICAL_SCROLLBAR_AS_NEEDED, HORIZONTAL_SCROLLBAR_AS_NEEDED);
    }


    /**
     * Returns the look and feel (L&F) object that renders this component.
     *
     * @return the <code>ScrollPaneUI object that renders this
     *                          component
     * @see #setUI
     * @beaninfo
     *        bound: true
     *       hidden: true
     *    attribute: visualUpdate true
     *  description: The UI object that implements the Component's LookAndFeel.
     */
    public ScrollPaneUI getUI() {
        return (ScrollPaneUI)ui;
    }


    /**
     * Sets the <code>ScrollPaneUI object that provides the
     * look and feel (L&F) for this component.
     *
     * @param ui the <code>ScrollPaneUI L&F object
     * @see #getUI
     */
    public void setUI(ScrollPaneUI ui) {
        super.setUI(ui);
    }


    /**
     * Replaces the current <code>ScrollPaneUI object with a version
     * from the current default look and feel.
     * To be called when the default look and feel changes.
     *
     * @see JComponent#updateUI
     * @see UIManager#getUI
     */
    public void updateUI() {
        setUI((ScrollPaneUI)UIManager.getUI(this));
    }


    /**
     * Returns the suffix used to construct the name of the L&F class used to
     * render this component.
     *
     * @return the string "ScrollPaneUI"
     * @see JComponent#getUIClassID
     * @see UIDefaults#getUI
     *
     * @beaninfo
     *    hidden: true
     */
    public String getUIClassID() {
        return uiClassID;
    }



    /**
     * Sets the layout manager for this <code>JScrollPane.
     * This method overrides <code>setLayout in
     * <code>java.awt.Container to ensure that only
     * <code>LayoutManagers which
     * are subclasses of <code>ScrollPaneLayout can be used in a
     * <code>JScrollPane. If layout is non-null, this
     * will invoke <code>syncWithScrollPane on it.
     *
     * @param layout the specified layout manager
     * @exception ClassCastException if layout is not a
     *                  <code>ScrollPaneLayout
     * @see java.awt.Container#getLayout
     * @see java.awt.Container#setLayout
     *
     * @beaninfo
     *    hidden: true
     */
    public void setLayout(LayoutManager layout) {
        if (layout instanceof ScrollPaneLayout) {
            super.setLayout(layout);
            ((ScrollPaneLayout)layout).syncWithScrollPane(this);
        }
        else if (layout == null) {
            super.setLayout(layout);
        }
        else {
            String s = "layout of JScrollPane must be a ScrollPaneLayout";
            throw new ClassCastException(s);
        }
    }

    /**
     * Overridden to return true so that any calls to <code>revalidate
     * on any descendants of this <code>JScrollPane will cause the
     * entire tree beginning with this <code>JScrollPane to be
     * validated.
     *
     * @return true
     * @see java.awt.Container#validate
     * @see JComponent#revalidate
     * @see JComponent#isValidateRoot
     * @see java.awt.Container#isValidateRoot
     *
     * @beaninfo
     *    hidden: true
     */
    @Override
    public boolean isValidateRoot() {
        return true;
    }


    /**
     * Returns the vertical scroll bar policy value.
     * @return the <code>verticalScrollBarPolicy property
     * @see #setVerticalScrollBarPolicy
     */
    public int getVerticalScrollBarPolicy() {
        return verticalScrollBarPolicy;
    }


    /**
     * Determines when the vertical scrollbar appears in the scrollpane.
     * Legal values are:
     * <ul>
     * <li>ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED
     * <li>ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER
     * <li>ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS
     * </ul>
     *
     * @param policy one of the three values listed above
     * @exception IllegalArgumentException if <code>policy
     *                          is not one of the legal values shown above
     * @see #getVerticalScrollBarPolicy
     *
     * @beaninfo
     *   preferred: true
     *       bound: true
     * description: The scrollpane vertical scrollbar policy
     *        enum: VERTICAL_SCROLLBAR_AS_NEEDED ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED
     *              VERTICAL_SCROLLBAR_NEVER ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER
     *              VERTICAL_SCROLLBAR_ALWAYS ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS
     */
    public void setVerticalScrollBarPolicy(int policy) {
        switch (policy) {
        case VERTICAL_SCROLLBAR_AS_NEEDED:
        case VERTICAL_SCROLLBAR_NEVER:
        case VERTICAL_SCROLLBAR_ALWAYS:
                break;
        default:
            throw new IllegalArgumentException("invalid verticalScrollBarPolicy");
        }
        int old = verticalScrollBarPolicy;
        verticalScrollBarPolicy = policy;
        firePropertyChange("verticalScrollBarPolicy", old, policy);
        revalidate();
        repaint();
    }


    /**
     * Returns the horizontal scroll bar policy value.
     * @return the <code>horizontalScrollBarPolicy property
     * @see #setHorizontalScrollBarPolicy
     */
    public int getHorizontalScrollBarPolicy() {
        return horizontalScrollBarPolicy;
    }


    /**
     * Determines when the horizontal scrollbar appears in the scrollpane.
     * The options are:<ul>
     * <li>ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED
     * <li>ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER
     * <li>ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS
     * </ul>
     *
     * @param policy one of the three values listed above
     * @exception IllegalArgumentException if <code>policy
     *                          is not one of the legal values shown above
     * @see #getHorizontalScrollBarPolicy
     *
     * @beaninfo
     *   preferred: true
     *       bound: true
     * description: The scrollpane scrollbar policy
     *        enum: HORIZONTAL_SCROLLBAR_AS_NEEDED ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED
     *              HORIZONTAL_SCROLLBAR_NEVER ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER
     *              HORIZONTAL_SCROLLBAR_ALWAYS ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS
     */
    public void setHorizontalScrollBarPolicy(int policy) {
        switch (policy) {
        case HORIZONTAL_SCROLLBAR_AS_NEEDED:
        case HORIZONTAL_SCROLLBAR_NEVER:
        case HORIZONTAL_SCROLLBAR_ALWAYS:
                break;
        default:
            throw new IllegalArgumentException("invalid horizontalScrollBarPolicy");
        }
        int old = horizontalScrollBarPolicy;
        horizontalScrollBarPolicy = policy;
        firePropertyChange("horizontalScrollBarPolicy", old, policy);
        revalidate();
        repaint();
    }


    /**
     * Returns the <code>Border object that surrounds the viewport.
     *
     * @return the <code>viewportBorder property
     * @see #setViewportBorder
     */
    public Border getViewportBorder() {
        return viewportBorder;
    }


    /**
     * Adds a border around the viewport.  Note that the border isn't
     * set on the viewport directly, <code>JViewport doesn't support
     * the <code>JComponent border property.
     * Similarly setting the <code>JScrollPanes
     * viewport doesn't affect the <code>viewportBorder property.
     * <p>
     * The default value of this property is computed by the look
     * and feel implementation.
     *
     * @param viewportBorder the border to be added
     * @see #getViewportBorder
     * @see #setViewport
     *
     * @beaninfo
     *   preferred: true
     *       bound: true
     * description: The border around the viewport.
     */
    public void setViewportBorder(Border viewportBorder) {
        Border oldValue = this.viewportBorder;
        this.viewportBorder = viewportBorder;
        firePropertyChange("viewportBorder", oldValue, viewportBorder);
    }


    /**
     * Returns the bounds of the viewport's border.
     *
     * @return a <code>Rectangle object specifying the viewport border
     */
    public Rectangle getViewportBorderBounds()
    {
        Rectangle borderR = new Rectangle(getSize());

        Insets insets = getInsets();
        borderR.x = insets.left;
        borderR.y = insets.top;
        borderR.width -= insets.left + insets.right;
        borderR.height -= insets.top + insets.bottom;

        boolean leftToRight = SwingUtilities.isLeftToRight(this);

        /* If there's a visible column header remove the space it
         * needs from the top of borderR.
         */

        JViewport colHead = getColumnHeader();
        if ((colHead != null) && (colHead.isVisible())) {
            int colHeadHeight = colHead.getHeight();
            borderR.y += colHeadHeight;
            borderR.height -= colHeadHeight;
        }

        /* If there's a visible row header remove the space it needs
         * from the left of borderR.
         */

        JViewport rowHead = getRowHeader();
        if ((rowHead != null) && (rowHead.isVisible())) {
            int rowHeadWidth = rowHead.getWidth();
            if ( leftToRight ) {
                borderR.x += rowHeadWidth;
            }
            borderR.width -= rowHeadWidth;
        }

        /* If there's a visible vertical scrollbar remove the space it needs
         * from the width of borderR.
         */
        JScrollBar vsb = getVerticalScrollBar();
        if ((vsb != null) && (vsb.isVisible())) {
            int vsbWidth = vsb.getWidth();
            if ( !leftToRight ) {
                borderR.x += vsbWidth;
            }
            borderR.width -= vsbWidth;
        }

        /* If there's a visible horizontal scrollbar remove the space it needs
         * from the height of borderR.
         */
        JScrollBar hsb = getHorizontalScrollBar();
        if ((hsb != null) && (hsb.isVisible())) {
            borderR.height -= hsb.getHeight();
        }

        return borderR;
    }


    /**
     * By default <code>JScrollPane creates scrollbars
     * that are instances
     * of this class.  <code>Scrollbar overrides the
     * <code>getUnitIncrement and getBlockIncrement
     * methods so that, if the viewport's view is a <code>Scrollable,
     * the view is asked to compute these values. Unless
     * the unit/block increment have been explicitly set.
     * <p>
     * <strong>Warning:
     * Serialized objects of this class will not be compatible with
     * future Swing releases. The current serialization support is
     * appropriate for short term storage or RMI between applications running
     * the same version of Swing.  As of 1.4, support for long term storage
     * of all JavaBeans™
     * has been added to the <code>java.beans package.
     * Please see {@link java.beans.XMLEncoder}.
     *
     * @see Scrollable
     * @see JScrollPane#createVerticalScrollBar
     * @see JScrollPane#createHorizontalScrollBar
     */
    protected class ScrollBar extends JScrollBar implements UIResource
    {
        /**
         * Set to true when the unit increment has been explicitly set.
         * If this is false the viewport's view is obtained and if it
         * is an instance of <code>Scrollable the unit increment
         * from it is used.
         */
        private boolean unitIncrementSet;
        /**
         * Set to true when the block increment has been explicitly set.
         * If this is false the viewport's view is obtained and if it
         * is an instance of <code>Scrollable the block increment
         * from it is used.
         */
        private boolean blockIncrementSet;

        /**
         * Creates a scrollbar with the specified orientation.
         * The options are:
         * <ul>
         * <li>ScrollPaneConstants.VERTICAL
         * <li>ScrollPaneConstants.HORIZONTAL
         * </ul>
         *
         * @param orientation  an integer specifying one of the legal
         *      orientation values shown above
         * @since 1.4
         */
        public ScrollBar(int orientation) {
            super(orientation);
            this.putClientProperty("JScrollBar.fastWheelScrolling",
                                   Boolean.TRUE);
        }

        /**
         * Messages super to set the value, and resets the
         * <code>unitIncrementSet instance variable to true.
         *
         * @param unitIncrement the new unit increment value, in pixels
         */
        public void setUnitIncrement(int unitIncrement) {
            unitIncrementSet = true;
            this.putClientProperty("JScrollBar.fastWheelScrolling", null);
            super.setUnitIncrement(unitIncrement);
        }

        /**
         * Computes the unit increment for scrolling if the viewport's
         * view is a <code>Scrollable object.
         * Otherwise return <code>super.getUnitIncrement.
         *
         * @param direction less than zero to scroll up/left,
         *      greater than zero for down/right
         * @return an integer, in pixels, containing the unit increment
         * @see Scrollable#getScrollableUnitIncrement
         */
        public int getUnitIncrement(int direction) {
            JViewport vp = getViewport();
            if (!unitIncrementSet && (vp != null) &&
                (vp.getView() instanceof Scrollable)) {
                Scrollable view = (Scrollable)(vp.getView());
                Rectangle vr = vp.getViewRect();
                return view.getScrollableUnitIncrement(vr, getOrientation(), direction);
            }
            else {
                return super.getUnitIncrement(direction);
            }
        }

        /**
         * Messages super to set the value, and resets the
         * <code>blockIncrementSet instance variable to true.
         *
         * @param blockIncrement the new block increment value, in pixels
         */
        public void setBlockIncrement(int blockIncrement) {
            blockIncrementSet = true;
            this.putClientProperty("JScrollBar.fastWheelScrolling", null);
            super.setBlockIncrement(blockIncrement);
        }

        /**
         * Computes the block increment for scrolling if the viewport's
         * view is a <code>Scrollable object.  Otherwise
         * the <code>blockIncrement equals the viewport's width
         * or height.  If there's no viewport return
         * <code>super.getBlockIncrement.
         *
         * @param direction less than zero to scroll up/left,
         *      greater than zero for down/right
         * @return an integer, in pixels, containing the block increment
         * @see Scrollable#getScrollableBlockIncrement
         */
        public int getBlockIncrement(int direction) {
            JViewport vp = getViewport();
            if (blockIncrementSet || vp == null) {
                return super.getBlockIncrement(direction);
            }
            else if (vp.getView() instanceof Scrollable) {
                Scrollable view = (Scrollable)(vp.getView());
                Rectangle vr = vp.getViewRect();
                return view.getScrollableBlockIncrement(vr, getOrientation(), direction);
            }
            else if (getOrientation() == VERTICAL) {
                return vp.getExtentSize().height;
            }
            else {
                return vp.getExtentSize().width;
            }
        }

    }


    /**
     * Returns a <code>JScrollPane.ScrollBar by default.
     * Subclasses may override this method to force <code>ScrollPaneUI
     * implementations to use a <code>JScrollBar subclass.
     * Used by <code>ScrollPaneUI implementations to
     * create the horizontal scrollbar.
     *
     * @return a <code>JScrollBar with a horizontal orientation
     * @see JScrollBar
     */
    public JScrollBar createHorizontalScrollBar() {
        return new ScrollBar(JScrollBar.HORIZONTAL);
    }


    /**
     * Returns the horizontal scroll bar that controls the viewport's
     * horizontal view position.
     *
     * @return the <code>horizontalScrollBar property
     * @see #setHorizontalScrollBar
     */
    @Transient
    public JScrollBar getHorizontalScrollBar() {
        return horizontalScrollBar;
    }


    /**
     * Adds the scrollbar that controls the viewport's horizontal view
     * position to the scrollpane.
     * This is usually unnecessary, as <code>JScrollPane creates
     * horizontal and vertical scrollbars by default.
     *
     * @param horizontalScrollBar the horizontal scrollbar to be added
     * @see #createHorizontalScrollBar
     * @see #getHorizontalScrollBar
     *
     * @beaninfo
     *        expert: true
     *         bound: true
     *   description: The horizontal scrollbar.
     */
    public void setHorizontalScrollBar(JScrollBar horizontalScrollBar) {
        JScrollBar old = getHorizontalScrollBar();
        this.horizontalScrollBar = horizontalScrollBar;
        if (horizontalScrollBar != null) {
            add(horizontalScrollBar, HORIZONTAL_SCROLLBAR);
        }
        else if (old != null) {
            remove(old);
        }
        firePropertyChange("horizontalScrollBar", old, horizontalScrollBar);

        revalidate();
        repaint();
    }


    /**
     * Returns a <code>JScrollPane.ScrollBar by default.  Subclasses
     * may override this method to force <code>ScrollPaneUI
     * implementations to use a <code>JScrollBar subclass.
     * Used by <code>ScrollPaneUI implementations to create the
     * vertical scrollbar.
     *
     * @return a <code>JScrollBar with a vertical orientation
     * @see JScrollBar
     */
    public JScrollBar createVerticalScrollBar() {
        return new ScrollBar(JScrollBar.VERTICAL);
    }


    /**
     * Returns the vertical scroll bar that controls the viewports
     * vertical view position.
     *
     * @return the <code>verticalScrollBar property
     * @see #setVerticalScrollBar
     */
    @Transient
    public JScrollBar getVerticalScrollBar() {
        return verticalScrollBar;
    }


    /**
     * Adds the scrollbar that controls the viewports vertical view position
     * to the scrollpane.  This is usually unnecessary,
     * as <code>JScrollPane creates vertical and
     * horizontal scrollbars by default.
     *
     * @param verticalScrollBar the new vertical scrollbar to be added
     * @see #createVerticalScrollBar
     * @see #getVerticalScrollBar
     *
     * @beaninfo
     *        expert: true
     *         bound: true
     *   description: The vertical scrollbar.
     */
    public void setVerticalScrollBar(JScrollBar verticalScrollBar) {
        JScrollBar old = getVerticalScrollBar();
        this.verticalScrollBar = verticalScrollBar;
        add(verticalScrollBar, VERTICAL_SCROLLBAR);
        firePropertyChange("verticalScrollBar", old, verticalScrollBar);

        revalidate();
        repaint();
    }


    /**
     * Returns a new <code>JViewport by default.
     * Used to create the
     * viewport (as needed) in <code>setViewportView,
     * <code>setRowHeaderView, and setColumnHeaderView.
     * Subclasses may override this method to return a subclass of
     * <code>JViewport.
     *
     * @return a new <code>JViewport
     */
    protected JViewport createViewport() {
        return new JViewport();
    }


    /**
     * Returns the current <code>JViewport.
     *
     * @see #setViewport
     * @return the <code>viewport property
     */
    public JViewport getViewport() {
        return viewport;
    }


    /**
     * Removes the old viewport (if there is one); forces the
     * viewPosition of the new viewport to be in the +x,+y quadrant;
     * syncs up the row and column headers (if there are any) with the
     * new viewport; and finally syncs the scrollbars and
     * headers with the new viewport.
     * <p>
     * Most applications will find it more convenient to use
     * <code>setViewportView
     * to add a viewport and a view to the scrollpane.
     *
     * @param viewport the new viewport to be used; if viewport is
     *          <code>null, the old viewport is still removed
     *          and the new viewport is set to <code>null
     * @see #createViewport
     * @see #getViewport
     * @see #setViewportView
     *
     * @beaninfo
     *       expert: true
     *        bound: true
     *    attribute: visualUpdate true
     *  description: The viewport child for this scrollpane
     *
     */
    public void setViewport(JViewport viewport) {
        JViewport old = getViewport();
        this.viewport = viewport;
        if (viewport != null) {
            add(viewport, VIEWPORT);
        }
        else if (old != null) {
            remove(old);
        }
        firePropertyChange("viewport", old, viewport);

        if (accessibleContext != null) {
            ((AccessibleJScrollPane)accessibleContext).resetViewPort();
        }

        revalidate();
        repaint();
    }


    /**
     * Creates a viewport if necessary and then sets its view.  Applications
     * that don't provide the view directly to the <code>JScrollPane
     * constructor
     * should use this method to specify the scrollable child that's going
     * to be displayed in the scrollpane. For example:
     * <pre>
     * JScrollPane scrollpane = new JScrollPane();
     * scrollpane.setViewportView(myBigComponentToScroll);
     * </pre>
     * Applications should not add children directly to the scrollpane.
     *
     * @param view the component to add to the viewport
     * @see #setViewport
     * @see JViewport#setView
     */
    public void setViewportView(Component view) {
        if (getViewport() == null) {
            setViewport(createViewport());
        }
        getViewport().setView(view);
    }



    /**
     * Returns the row header.
     * @return the <code>rowHeader property
     * @see #setRowHeader
     */
    @Transient
    public JViewport getRowHeader() {
        return rowHeader;
    }


    /**
     * Removes the old rowHeader, if it exists; if the new rowHeader
     * isn't <code>null, syncs the y coordinate of its
     * viewPosition with
     * the viewport (if there is one) and then adds it to the scroll pane.
     * <p>
     * Most applications will find it more convenient to use
     * <code>setRowHeaderView
     * to add a row header component and its viewport to the scroll pane.
     *
     * @param rowHeader the new row header to be used; if <code>null
     *          the old row header is still removed and the new rowHeader
     *          is set to <code>null
     * @see #getRowHeader
     * @see #setRowHeaderView
     *
     * @beaninfo
     *        bound: true
     *       expert: true
     *  description: The row header child for this scrollpane
     */
    public void setRowHeader(JViewport rowHeader) {
        JViewport old = getRowHeader();
        this.rowHeader = rowHeader;
        if (rowHeader != null) {
            add(rowHeader, ROW_HEADER);
        }
        else if (old != null) {
            remove(old);
        }
        firePropertyChange("rowHeader", old, rowHeader);
        revalidate();
        repaint();
    }


    /**
     * Creates a row-header viewport if necessary, sets
     * its view and then adds the row-header viewport
     * to the scrollpane.  For example:
     * <pre>
     * JScrollPane scrollpane = new JScrollPane();
     * scrollpane.setViewportView(myBigComponentToScroll);
     * scrollpane.setRowHeaderView(myBigComponentsRowHeader);
     * </pre>
     *
     * @see #setRowHeader
     * @see JViewport#setView
     * @param view the component to display as the row header
     */
    public void setRowHeaderView(Component view) {
        if (getRowHeader() == null) {
            setRowHeader(createViewport());
        }
        getRowHeader().setView(view);
    }



    /**
     * Returns the column header.
     * @return the <code>columnHeader property
     * @see #setColumnHeader
     */
    @Transient
    public JViewport getColumnHeader() {
        return columnHeader;
    }


    /**
     * Removes the old columnHeader, if it exists; if the new columnHeader
     * isn't <code>null, syncs the x coordinate of its viewPosition
     * with the viewport (if there is one) and then adds it to the scroll pane.
     * <p>
     * Most applications will find it more convenient to use
     * <code>setColumnHeaderView
     * to add a column header component and its viewport to the scroll pane.
     *
     * @see #getColumnHeader
     * @see #setColumnHeaderView
     *
     * @beaninfo
     *        bound: true
     *  description: The column header child for this scrollpane
     *    attribute: visualUpdate true
     */
    public void setColumnHeader(JViewport columnHeader) {
        JViewport old = getColumnHeader();
        this.columnHeader = columnHeader;
        if (columnHeader != null) {
            add(columnHeader, COLUMN_HEADER);
        }
        else if (old != null) {
            remove(old);
        }
        firePropertyChange("columnHeader", old, columnHeader);

        revalidate();
        repaint();
    }



    /**
     * Creates a column-header viewport if necessary, sets
     * its view, and then adds the column-header viewport
     * to the scrollpane.  For example:
     * <pre>
     * JScrollPane scrollpane = new JScrollPane();
     * scrollpane.setViewportView(myBigComponentToScroll);
     * scrollpane.setColumnHeaderView(myBigComponentsColumnHeader);
     * </pre>
     *
     * @see #setColumnHeader
     * @see JViewport#setView
     *
     * @param view the component to display as the column header
     */
    public void setColumnHeaderView(Component view) {
        if (getColumnHeader() == null) {
            setColumnHeader(createViewport());
        }
        getColumnHeader().setView(view);
    }


    /**
     * Returns the component at the specified corner. The
     * <code>key value specifying the corner is one of:
     * <ul>
     * <li>ScrollPaneConstants.LOWER_LEFT_CORNER
     * <li>ScrollPaneConstants.LOWER_RIGHT_CORNER
     * <li>ScrollPaneConstants.UPPER_LEFT_CORNER
     * <li>ScrollPaneConstants.UPPER_RIGHT_CORNER
     * <li>ScrollPaneConstants.LOWER_LEADING_CORNER
     * <li>ScrollPaneConstants.LOWER_TRAILING_CORNER
     * <li>ScrollPaneConstants.UPPER_LEADING_CORNER
     * <li>ScrollPaneConstants.UPPER_TRAILING_CORNER
     * </ul>
     *
     * @param key one of the values as shown above
     * @return the corner component (which may be <code>null)
     *         identified by the given key, or <code>null
     *         if the key is invalid
     * @see #setCorner
     */
    public Component getCorner(String key) {
        boolean isLeftToRight = getComponentOrientation().isLeftToRight();
        if (key.equals(LOWER_LEADING_CORNER)) {
            key = isLeftToRight ? LOWER_LEFT_CORNER : LOWER_RIGHT_CORNER;
        } else if (key.equals(LOWER_TRAILING_CORNER)) {
            key = isLeftToRight ? LOWER_RIGHT_CORNER : LOWER_LEFT_CORNER;
        } else if (key.equals(UPPER_LEADING_CORNER)) {
            key = isLeftToRight ? UPPER_LEFT_CORNER : UPPER_RIGHT_CORNER;
        } else if (key.equals(UPPER_TRAILING_CORNER)) {
            key = isLeftToRight ? UPPER_RIGHT_CORNER : UPPER_LEFT_CORNER;
        }
        if (key.equals(LOWER_LEFT_CORNER)) {
            return lowerLeft;
        }
        else if (key.equals(LOWER_RIGHT_CORNER)) {
            return lowerRight;
        }
        else if (key.equals(UPPER_LEFT_CORNER)) {
            return upperLeft;
        }
        else if (key.equals(UPPER_RIGHT_CORNER)) {
            return upperRight;
        }
        else {
            return null;
        }
    }


    /**
     * Adds a child that will appear in one of the scroll panes
     * corners, if there's room.   For example with both scrollbars
     * showing (on the right and bottom edges of the scrollpane)
     * the lower left corner component will be shown in the space
     * between ends of the two scrollbars. Legal values for
     * the <b>key are:
     * <ul>
     * <li>ScrollPaneConstants.LOWER_LEFT_CORNER
     * <li>ScrollPaneConstants.LOWER_RIGHT_CORNER
     * <li>ScrollPaneConstants.UPPER_LEFT_CORNER
     * <li>ScrollPaneConstants.UPPER_RIGHT_CORNER
     * <li>ScrollPaneConstants.LOWER_LEADING_CORNER
     * <li>ScrollPaneConstants.LOWER_TRAILING_CORNER
     * <li>ScrollPaneConstants.UPPER_LEADING_CORNER
     * <li>ScrollPaneConstants.UPPER_TRAILING_CORNER
     * </ul>
     * <p>
     * Although "corner" doesn't match any beans property
     * signature, <code>PropertyChange events are generated with the
     * property name set to the corner key.
     *
     * @param key identifies which corner the component will appear in
     * @param corner one of the following components:
     * <ul>
     * <li>lowerLeft
     * <li>lowerRight
     * <li>upperLeft
     * <li>upperRight
     * </ul>
     * @exception IllegalArgumentException if corner key is invalid
     */
    public void setCorner(String key, Component corner)
    {
        Component old;
        boolean isLeftToRight = getComponentOrientation().isLeftToRight();
        if (key.equals(LOWER_LEADING_CORNER)) {
            key = isLeftToRight ? LOWER_LEFT_CORNER : LOWER_RIGHT_CORNER;
        } else if (key.equals(LOWER_TRAILING_CORNER)) {
            key = isLeftToRight ? LOWER_RIGHT_CORNER : LOWER_LEFT_CORNER;
        } else if (key.equals(UPPER_LEADING_CORNER)) {
            key = isLeftToRight ? UPPER_LEFT_CORNER : UPPER_RIGHT_CORNER;
        } else if (key.equals(UPPER_TRAILING_CORNER)) {
            key = isLeftToRight ? UPPER_RIGHT_CORNER : UPPER_LEFT_CORNER;
        }
        if (key.equals(LOWER_LEFT_CORNER)) {
            old = lowerLeft;
            lowerLeft = corner;
        }
        else if (key.equals(LOWER_RIGHT_CORNER)) {
            old = lowerRight;
            lowerRight = corner;
        }
        else if (key.equals(UPPER_LEFT_CORNER)) {
            old = upperLeft;
            upperLeft = corner;
        }
        else if (key.equals(UPPER_RIGHT_CORNER)) {
            old = upperRight;
            upperRight = corner;
        }
        else {
            throw new IllegalArgumentException("invalid corner key");
        }
        if (old != null) {
            remove(old);
        }
        if (corner != null) {
            add(corner, key);
        }
        firePropertyChange(key, old, corner);
        revalidate();
        repaint();
    }

    /**
     * Sets the orientation for the vertical and horizontal
     * scrollbars as determined by the
     * <code>ComponentOrientation argument.
     *
     * @param  co one of the following values:
     * <ul>
     * <li>java.awt.ComponentOrientation.LEFT_TO_RIGHT
     * <li>java.awt.ComponentOrientation.RIGHT_TO_LEFT
     * <li>java.awt.ComponentOrientation.UNKNOWN
     * </ul>
     * @see java.awt.ComponentOrientation
     */
    public void setComponentOrientation( ComponentOrientation co ) {
        super.setComponentOrientation( co );
        if( verticalScrollBar != null )
            verticalScrollBar.setComponentOrientation( co );
        if( horizontalScrollBar != null )
            horizontalScrollBar.setComponentOrientation( co );
    }

    /**
     * Indicates whether or not scrolling will take place in response to the
     * mouse wheel.  Wheel scrolling is enabled by default.
     *
     * @see #setWheelScrollingEnabled
     * @since 1.4
     * @beaninfo
     *       bound: true
     * description: Flag for enabling/disabling mouse wheel scrolling
     */
    public boolean isWheelScrollingEnabled() {return wheelScrollState;}

    /**
     * Enables/disables scrolling in response to movement of the mouse wheel.
     * Wheel scrolling is enabled by default.
     *
     * @param handleWheel   <code>true if scrolling should be done
     *                      automatically for a MouseWheelEvent,
     *                      <code>false otherwise.
     * @see #isWheelScrollingEnabled
     * @see java.awt.event.MouseWheelEvent
     * @see java.awt.event.MouseWheelListener
     * @since 1.4
     * @beaninfo
     *       bound: true
     * description: Flag for enabling/disabling mouse wheel scrolling
     */
    public void setWheelScrollingEnabled(boolean handleWheel) {
        boolean old = wheelScrollState;
        wheelScrollState = handleWheel;
        firePropertyChange("wheelScrollingEnabled", old, handleWheel);
    }

    /**
     * See <code>readObject and writeObject in
     * <code>JComponent for more
     * information about serialization in Swing.
     */
    private void writeObject(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        if (getUIClassID().equals(uiClassID)) {
            byte count = JComponent.getWriteObjCounter(this);
            JComponent.setWriteObjCounter(this, --count);
            if (count == 0 && ui != null) {
                ui.installUI(this);
            }
        }
    }


    /**
     * Returns a string representation of this <code>JScrollPane.
     * This method
     * is intended to be used only for debugging purposes, and the
     * content and format of the returned string may vary between
     * implementations. The returned string may be empty but may not
     * be <code>null.
     *
     * @return  a string representation of this <code>JScrollPane.
     */
    protected String paramString() {
        String viewportBorderString = (viewportBorder != null ?
                                       viewportBorder.toString() : "");
        String viewportString = (viewport != null ?
                                 viewport.toString() : "");
        String verticalScrollBarPolicyString;
        if (verticalScrollBarPolicy == VERTICAL_SCROLLBAR_AS_NEEDED) {
            verticalScrollBarPolicyString = "VERTICAL_SCROLLBAR_AS_NEEDED";
        } else if (verticalScrollBarPolicy == VERTICAL_SCROLLBAR_NEVER) {
            verticalScrollBarPolicyString = "VERTICAL_SCROLLBAR_NEVER";
        } else if (verticalScrollBarPolicy == VERTICAL_SCROLLBAR_ALWAYS) {
            verticalScrollBarPolicyString = "VERTICAL_SCROLLBAR_ALWAYS";
        } else verticalScrollBarPolicyString = "";
        String horizontalScrollBarPolicyString;
        if (horizontalScrollBarPolicy == HORIZONTAL_SCROLLBAR_AS_NEEDED) {
            horizontalScrollBarPolicyString = "HORIZONTAL_SCROLLBAR_AS_NEEDED";
        } else if (horizontalScrollBarPolicy == HORIZONTAL_SCROLLBAR_NEVER) {
            horizontalScrollBarPolicyString = "HORIZONTAL_SCROLLBAR_NEVER";
        } else if (horizontalScrollBarPolicy == HORIZONTAL_SCROLLBAR_ALWAYS) {
            horizontalScrollBarPolicyString = "HORIZONTAL_SCROLLBAR_ALWAYS";
        } else horizontalScrollBarPolicyString = "";
        String horizontalScrollBarString = (horizontalScrollBar != null ?
                                            horizontalScrollBar.toString()
                                            : "");
        String verticalScrollBarString = (verticalScrollBar != null ?
                                          verticalScrollBar.toString() : "");
        String columnHeaderString = (columnHeader != null ?
                                     columnHeader.toString() : "");
        String rowHeaderString = (rowHeader != null ?
                                  rowHeader.toString() : "");
        String lowerLeftString = (lowerLeft != null ?
                                  lowerLeft.toString() : "");
        String lowerRightString = (lowerRight != null ?
                                  lowerRight.toString() : "");
        String upperLeftString = (upperLeft != null ?
                                  upperLeft.toString() : "");
        String upperRightString = (upperRight != null ?
                                  upperRight.toString() : "");

        return super.paramString() +
        ",columnHeader=" + columnHeaderString +
        ",horizontalScrollBar=" + horizontalScrollBarString +
        ",horizontalScrollBarPolicy=" + horizontalScrollBarPolicyString +
        ",lowerLeft=" + lowerLeftString +
        ",lowerRight=" + lowerRightString +
        ",rowHeader=" + rowHeaderString +
        ",upperLeft=" + upperLeftString +
        ",upperRight=" + upperRightString +
        ",verticalScrollBar=" + verticalScrollBarString +
        ",verticalScrollBarPolicy=" + verticalScrollBarPolicyString +
        ",viewport=" + viewportString +
        ",viewportBorder=" + viewportBorderString;
    }

/////////////////
// Accessibility support
////////////////

    /**
     * Gets the AccessibleContext associated with this JScrollPane.
     * For scroll panes, the AccessibleContext takes the form of an
     * AccessibleJScrollPane.
     * A new AccessibleJScrollPane instance is created if necessary.
     *
     * @return an AccessibleJScrollPane that serves as the
     *         AccessibleContext of this JScrollPane
     */
    public AccessibleContext getAccessibleContext() {
        if (accessibleContext == null) {
            accessibleContext = new AccessibleJScrollPane();
        }
        return accessibleContext;
    }

    /**
     * This class implements accessibility support for the
     * <code>JScrollPane class.  It provides an implementation of the
     * Java Accessibility API appropriate to scroll pane user-interface
     * elements.
     * <p>
     * <strong>Warning:
     * Serialized objects of this class will not be compatible with
     * future Swing releases. The current serialization support is
     * appropriate for short term storage or RMI between applications running
     * the same version of Swing.  As of 1.4, support for long term storage
     * of all JavaBeans™
     * has been added to the <code>java.beans package.
     * Please see {@link java.beans.XMLEncoder}.
     */
    protected class AccessibleJScrollPane extends AccessibleJComponent
        implements ChangeListener, PropertyChangeListener {

        protected JViewport viewPort = null;

        /*
         * Resets the viewport ChangeListener and PropertyChangeListener
         */
        public void resetViewPort() {
            if (viewPort != null) {
                viewPort.removeChangeListener(this);
                viewPort.removePropertyChangeListener(this);
            }
            viewPort = JScrollPane.this.getViewport();
            if (viewPort != null) {
                viewPort.addChangeListener(this);
                viewPort.addPropertyChangeListener(this);
            }
        }

        /**
         * AccessibleJScrollPane constructor
         */
        public AccessibleJScrollPane() {
            super();

            resetViewPort();

            // initialize the AccessibleRelationSets for the JScrollPane
            // and JScrollBar(s)
            JScrollBar scrollBar = getHorizontalScrollBar();
            if (scrollBar != null) {
                setScrollBarRelations(scrollBar);
            }
            scrollBar = getVerticalScrollBar();
            if (scrollBar != null) {
                setScrollBarRelations(scrollBar);
            }
        }

        /**
         * Get the role of this object.
         *
         * @return an instance of AccessibleRole describing the role of the
         * object
         * @see AccessibleRole
         */
        public AccessibleRole getAccessibleRole() {
            return AccessibleRole.SCROLL_PANE;
        }

        /**
         * Invoked when the target of the listener has changed its state.
         *
         * @param e  a <code>ChangeEvent object. Must not be null.
         *
         * @throws NullPointerException if the parameter is null.
         */
        public void stateChanged(ChangeEvent e) {
            if (e == null) {
                throw new NullPointerException();
            }
            firePropertyChange(ACCESSIBLE_VISIBLE_DATA_PROPERTY,
                               Boolean.valueOf(false),
                               Boolean.valueOf(true));
        }

        /**
         * This method gets called when a bound property is changed.
         * @param e A <code>PropertyChangeEvent object describing
         * the event source and the property that has changed. Must not be null.
         *
         * @throws NullPointerException if the parameter is null.
         * @since 1.5
         */
        public void propertyChange(PropertyChangeEvent e) {
            String propertyName = e.getPropertyName();
            if (propertyName == "horizontalScrollBar" ||
                propertyName == "verticalScrollBar") {

                if (e.getNewValue() instanceof JScrollBar) {
                    setScrollBarRelations((JScrollBar)e.getNewValue());
                }
            }
        }


        /*
         * Sets the CONTROLLER_FOR and CONTROLLED_BY AccessibleRelations for
         * the JScrollPane and JScrollBar. JScrollBar must not be null.
         */
        void setScrollBarRelations(JScrollBar scrollBar) {
            /*
             * The JScrollBar is a CONTROLLER_FOR the JScrollPane.
             * The JScrollPane is CONTROLLED_BY the JScrollBar.
             */
            AccessibleRelation controlledBy =
                new AccessibleRelation(AccessibleRelation.CONTROLLED_BY,
                                       scrollBar);
            AccessibleRelation controllerFor =
                new AccessibleRelation(AccessibleRelation.CONTROLLER_FOR,
                                       JScrollPane.this);

            // set the relation set for the scroll bar
            AccessibleContext ac = scrollBar.getAccessibleContext();
            ac.getAccessibleRelationSet().add(controllerFor);

            // set the relation set for the scroll pane
            getAccessibleRelationSet().add(controlledBy);
        }
    }
}