https://openjdk.java.net/ 
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 * 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
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 *
 * 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).
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 *
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package java.awt;

import java.awt.peer.ScrollPanePeer;
import java.awt.event.*;
import javax.accessibility.*;
import sun.awt.ScrollPaneWheelScroller;
import sun.awt.SunToolkit;

import java.beans.ConstructorProperties;
import java.beans.Transient;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.IOException;


A container class which implements automatic horizontal and/or
vertical scrolling for a single child component.  The display
policy for the scrollbars can be set to:

    

  1. as needed: scrollbars created and shown only when needed by scrollpane

  2. always: scrollbars created and always shown by the scrollpane

  3. never: scrollbars never created or shown by the scrollpane



 The state of the horizontal and vertical scrollbars is represented by two ScrollPaneAdjustable objects (one for each dimension) which implement the Adjustable interface. The API provides methods to access those objects such that the attributes on the Adjustable object (such as unitIncrement, value, etc.) can be manipulated. 

Certain adjustable properties (minimum, maximum, blockIncrement,
and visibleAmount) are set internally by the scrollpane in accordance
with the geometry of the scrollpane and its child and these should
not be set by programs using the scrollpane.


If the scrollbar display policy is defined as "never", then the
scrollpane can still be programmatically scrolled using the
setScrollPosition() method and the scrollpane will move and clip
the child's contents appropriately.  This policy is useful if the
program needs to create and manage its own adjustable controls.


The placement of the scrollbars is controlled by platform-specific
properties set by the user outside of the program.


The initial size of this container is set to 100x100, but can
be reset using setSize().

 Scrolling with the wheel on a wheel-equipped mouse is enabled by default. This can be disabled using setWheelScrollingEnabled. Wheel scrolling can be customized by setting the block and unit increment of the horizontal and vertical Adjustables. For information on how mouse wheel events are dispatched, see the class description for MouseWheelEvent. 

Insets are used to define any space used by scrollbars and any
borders created by the scroll pane. getInsets() can be used
to get the current value for the insets.  If the value of
scrollbarsAlwaysVisible is false, then the value of the insets
will change dynamically depending on whether the scrollbars are
currently visible or not.

Author:     Tom Ball,      Amy Fowler,      Tim Prinzing
/**
 * A container class which implements automatic horizontal and/or
 * vertical scrolling for a single child component.  The display
 * policy for the scrollbars can be set to:
 * <OL>
 * <LI>as needed: scrollbars created and shown only when needed by scrollpane
 * <LI>always: scrollbars created and always shown by the scrollpane
 * <LI>never: scrollbars never created or shown by the scrollpane
 * </OL>
 * <P>
 * The state of the horizontal and vertical scrollbars is represented
 * by two {@code ScrollPaneAdjustable} objects (one for each
 * dimension) which implement the {@code Adjustable} interface.
 * The API provides methods to access those objects such that the
 * attributes on the Adjustable object (such as unitIncrement, value,
 * etc.) can be manipulated.
 * <P>
 * Certain adjustable properties (minimum, maximum, blockIncrement,
 * and visibleAmount) are set internally by the scrollpane in accordance
 * with the geometry of the scrollpane and its child and these should
 * not be set by programs using the scrollpane.
 * <P>
 * If the scrollbar display policy is defined as "never", then the
 * scrollpane can still be programmatically scrolled using the
 * setScrollPosition() method and the scrollpane will move and clip
 * the child's contents appropriately.  This policy is useful if the
 * program needs to create and manage its own adjustable controls.
 * <P>
 * The placement of the scrollbars is controlled by platform-specific
 * properties set by the user outside of the program.
 * <P>
 * The initial size of this container is set to 100x100, but can
 * be reset using setSize().
 * <P>
 * Scrolling with the wheel on a wheel-equipped mouse is enabled by default.
 * This can be disabled using {@code setWheelScrollingEnabled}.
 * Wheel scrolling can be customized by setting the block and
 * unit increment of the horizontal and vertical Adjustables.
 * For information on how mouse wheel events are dispatched, see
 * the class description for {@link MouseWheelEvent}.
 * <P>
 * Insets are used to define any space used by scrollbars and any
 * borders created by the scroll pane. getInsets() can be used
 * to get the current value for the insets.  If the value of
 * scrollbarsAlwaysVisible is false, then the value of the insets
 * will change dynamically depending on whether the scrollbars are
 * currently visible or not.
 *
 * @author      Tom Ball
 * @author      Amy Fowler
 * @author      Tim Prinzing
 */
public class ScrollPane extends Container implements Accessible {


    
Initialize JNI field and method IDs

/**
     * Initialize JNI field and method IDs
     */
    private static native void initIDs();

    static {
        /* ensure that the necessary native libraries are loaded */
        Toolkit.loadLibraries();
        if (!GraphicsEnvironment.isHeadless()) {
            initIDs();
        }
    }

    
Specifies that horizontal/vertical scrollbar should be shown
only when the size of the child exceeds the size of the scrollpane
in the horizontal/vertical dimension.

/**
     * Specifies that horizontal/vertical scrollbar should be shown
     * only when the size of the child exceeds the size of the scrollpane
     * in the horizontal/vertical dimension.
     */
    public static final int SCROLLBARS_AS_NEEDED = 0;

    
Specifies that horizontal/vertical scrollbars should always be
shown regardless of the respective sizes of the scrollpane and child.

/**
     * Specifies that horizontal/vertical scrollbars should always be
     * shown regardless of the respective sizes of the scrollpane and child.
     */
    public static final int SCROLLBARS_ALWAYS = 1;

    
Specifies that horizontal/vertical scrollbars should never be shown
regardless of the respective sizes of the scrollpane and child.

/**
     * Specifies that horizontal/vertical scrollbars should never be shown
     * regardless of the respective sizes of the scrollpane and child.
     */
    public static final int SCROLLBARS_NEVER = 2;

    
There are 3 ways in which a scroll bar can be displayed.
This integer will represent one of these 3 displays -
(SCROLLBARS_ALWAYS, SCROLLBARS_AS_NEEDED, SCROLLBARS_NEVER)

See Also:
@serial
/**
     * There are 3 ways in which a scroll bar can be displayed.
     * This integer will represent one of these 3 displays -
     * (SCROLLBARS_ALWAYS, SCROLLBARS_AS_NEEDED, SCROLLBARS_NEVER)
     *
     * @serial
     * @see #getScrollbarDisplayPolicy
     */
    private int scrollbarDisplayPolicy;

    
An adjustable vertical scrollbar.
It is important to note that you must NOT call 3 Adjustable methods, namely: setMinimum(), setMaximum(), setVisibleAmount(). 
See Also:
@serial
/**
     * An adjustable vertical scrollbar.
     * It is important to note that you must <em>NOT</em> call 3
     * {@code Adjustable} methods, namely:
     * {@code setMinimum()}, {@code setMaximum()},
     * {@code setVisibleAmount()}.
     *
     * @serial
     * @see #getVAdjustable
     */
    private ScrollPaneAdjustable vAdjustable;

    
An adjustable horizontal scrollbar.
It is important to note that you must NOT call 3 Adjustable methods, namely: setMinimum(), setMaximum(), setVisibleAmount(). 
See Also:
@serial
/**
     * An adjustable horizontal scrollbar.
     * It is important to note that you must <em>NOT</em> call 3
     * {@code Adjustable} methods, namely:
     * {@code setMinimum()}, {@code setMaximum()},
     * {@code setVisibleAmount()}.
     *
     * @serial
     * @see #getHAdjustable
     */
    private ScrollPaneAdjustable hAdjustable;

    private static final String base = "scrollpane";
    private static int nameCounter = 0;

    private static final boolean defaultWheelScroll = true;

    
Indicates whether or not scrolling should take place when a
MouseWheelEvent is received.

@serial
Since:1.4
/**
     * Indicates whether or not scrolling should take place when a
     * MouseWheelEvent is received.
     *
     * @serial
     * @since 1.4
     */
    private boolean wheelScrollingEnabled = defaultWheelScroll;

    /*
     * JDK 1.1 serialVersionUID
     */
    private static final long serialVersionUID = 7956609840827222915L;

    
Create a new scrollpane container with a scrollbar display
policy of "as needed".

Throws:
  • HeadlessException – if GraphicsEnvironment.isHeadless()
    returns true
See Also:
/**
     * Create a new scrollpane container with a scrollbar display
     * policy of "as needed".
     * @throws HeadlessException if GraphicsEnvironment.isHeadless()
     *     returns true
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public ScrollPane() throws HeadlessException {
        this(SCROLLBARS_AS_NEEDED);
    }

    
Create a new scrollpane container.

Params:
  • scrollbarDisplayPolicy – policy for when scrollbars should be shown
Throws:
See Also:
/**
     * Create a new scrollpane container.
     * @param scrollbarDisplayPolicy policy for when scrollbars should be shown
     * @throws IllegalArgumentException if the specified scrollbar
     *     display policy is invalid
     * @throws HeadlessException if GraphicsEnvironment.isHeadless()
     *     returns true
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    @ConstructorProperties({"scrollbarDisplayPolicy"})
    public ScrollPane(int scrollbarDisplayPolicy) throws HeadlessException {
        GraphicsEnvironment.checkHeadless();
        this.layoutMgr = null;
        this.width = 100;
        this.height = 100;
        switch (scrollbarDisplayPolicy) {
            case SCROLLBARS_NEVER:
            case SCROLLBARS_AS_NEEDED:
            case SCROLLBARS_ALWAYS:
                this.scrollbarDisplayPolicy = scrollbarDisplayPolicy;
                break;
            default:
                throw new IllegalArgumentException("illegal scrollbar display policy");
        }

        vAdjustable = new ScrollPaneAdjustable(this, new PeerFixer(this),
                                               Adjustable.VERTICAL);
        hAdjustable = new ScrollPaneAdjustable(this, new PeerFixer(this),
                                               Adjustable.HORIZONTAL);
        setWheelScrollingEnabled(defaultWheelScroll);
    }

    
Construct a name for this component.  Called by getName() when the
name is null.

/**
     * Construct a name for this component.  Called by getName() when the
     * name is null.
     */
    String constructComponentName() {
        synchronized (ScrollPane.class) {
            return base + nameCounter++;
        }
    }

    // The scrollpane won't work with a windowless child... it assumes
    // it is moving a child window around so the windowless child is
    // wrapped with a window.
    private void addToPanel(Component comp, Object constraints, int index) {
        Panel child = new Panel();
        child.setLayout(new BorderLayout());
        child.add(comp);
        super.addImpl(child, constraints, index);
        validate();
    }

    
Adds the specified component to this scroll pane container.
If the scroll pane has an existing child component, that
component is removed and the new one is added.

Params:
  • comp – the component to be added
  • constraints –  not applicable
  • index – position of child component (must be <= 0)
/**
     * Adds the specified component to this scroll pane container.
     * If the scroll pane has an existing child component, that
     * component is removed and the new one is added.
     * @param comp the component to be added
     * @param constraints  not applicable
     * @param index position of child component (must be &lt;= 0)
     */
    protected final void addImpl(Component comp, Object constraints, int index) {
        synchronized (getTreeLock()) {
            if (getComponentCount() > 0) {
                remove(0);
            }
            if (index > 0) {
                throw new IllegalArgumentException("position greater than 0");
            }

            if (!SunToolkit.isLightweightOrUnknown(comp)) {
                super.addImpl(comp, constraints, index);
            } else {
                addToPanel(comp, constraints, index);
            }
        }
    }

    
Returns the display policy for the scrollbars.

Returns:the display policy for the scrollbars
/**
     * Returns the display policy for the scrollbars.
     * @return the display policy for the scrollbars
     */
    public int getScrollbarDisplayPolicy() {
        return scrollbarDisplayPolicy;
    }

    
Returns the current size of the scroll pane's view port.

Returns:the size of the view port in pixels
/**
     * Returns the current size of the scroll pane's view port.
     * @return the size of the view port in pixels
     */
    public Dimension getViewportSize() {
        Insets i = getInsets();
        return new Dimension(width - i.right - i.left,
                             height - i.top - i.bottom);
    }

    
Returns the height that would be occupied by a horizontal
scrollbar, which is independent of whether it is currently
displayed by the scroll pane or not.

Returns:the height of a horizontal scrollbar in pixels
/**
     * Returns the height that would be occupied by a horizontal
     * scrollbar, which is independent of whether it is currently
     * displayed by the scroll pane or not.
     * @return the height of a horizontal scrollbar in pixels
     */
    public int getHScrollbarHeight() {
        int h = 0;
        if (scrollbarDisplayPolicy != SCROLLBARS_NEVER) {
            ScrollPanePeer peer = (ScrollPanePeer)this.peer;
            if (peer != null) {
                h = peer.getHScrollbarHeight();
            }
        }
        return h;
    }

    
Returns the width that would be occupied by a vertical
scrollbar, which is independent of whether it is currently
displayed by the scroll pane or not.

Returns:the width of a vertical scrollbar in pixels
/**
     * Returns the width that would be occupied by a vertical
     * scrollbar, which is independent of whether it is currently
     * displayed by the scroll pane or not.
     * @return the width of a vertical scrollbar in pixels
     */
    public int getVScrollbarWidth() {
        int w = 0;
        if (scrollbarDisplayPolicy != SCROLLBARS_NEVER) {
            ScrollPanePeer peer = (ScrollPanePeer)this.peer;
            if (peer != null) {
                w = peer.getVScrollbarWidth();
            }
        }
        return w;
    }

    
Returns the ScrollPaneAdjustable object which represents the state of the vertical scrollbar. The declared return type of this method is Adjustable to maintain backward compatibility. 
See Also:
Returns:the vertical scrollbar state
/**
     * Returns the {@code ScrollPaneAdjustable} object which
     * represents the state of the vertical scrollbar.
     * The declared return type of this method is
     * {@code Adjustable} to maintain backward compatibility.
     *
     * @see java.awt.ScrollPaneAdjustable
     * @return the vertical scrollbar state
     */
    public Adjustable getVAdjustable() {
        return vAdjustable;
    }

    
Returns the ScrollPaneAdjustable object which represents the state of the horizontal scrollbar. The declared return type of this method is Adjustable to maintain backward compatibility. 
See Also:
Returns:the horizontal scrollbar state
/**
     * Returns the {@code ScrollPaneAdjustable} object which
     * represents the state of the horizontal scrollbar.
     * The declared return type of this method is
     * {@code Adjustable} to maintain backward compatibility.
     *
     * @see java.awt.ScrollPaneAdjustable
     * @return the horizontal scrollbar state
     */
    public Adjustable getHAdjustable() {
        return hAdjustable;
    }

    
Scrolls to the specified position within the child component.
A call to this method is only valid if the scroll pane contains
a child.  Specifying a position outside of the legal scrolling bounds
of the child will scroll to the closest legal position.
Legal bounds are defined to be the rectangle:
x = 0, y = 0, width = (child width - view port width),
height = (child height - view port height).
This is a convenience method which interfaces with the Adjustable
objects which represent the state of the scrollbars.

Params:
  • x – the x position to scroll to
  • y – the y position to scroll to
Throws:
/**
     * Scrolls to the specified position within the child component.
     * A call to this method is only valid if the scroll pane contains
     * a child.  Specifying a position outside of the legal scrolling bounds
     * of the child will scroll to the closest legal position.
     * Legal bounds are defined to be the rectangle:
     * x = 0, y = 0, width = (child width - view port width),
     * height = (child height - view port height).
     * This is a convenience method which interfaces with the Adjustable
     * objects which represent the state of the scrollbars.
     * @param x the x position to scroll to
     * @param y the y position to scroll to
     * @throws NullPointerException if the scrollpane does not contain
     *     a child
     */
    public void setScrollPosition(int x, int y) {
        synchronized (getTreeLock()) {
            if (getComponentCount()==0) {
                throw new NullPointerException("child is null");
            }
            hAdjustable.setValue(x);
            vAdjustable.setValue(y);
        }
    }

    
Scrolls to the specified position within the child component.
A call to this method is only valid if the scroll pane contains
a child and the specified position is within legal scrolling bounds
of the child.  Specifying a position outside of the legal scrolling
bounds of the child will scroll to the closest legal position.
Legal bounds are defined to be the rectangle:
x = 0, y = 0, width = (child width - view port width),
height = (child height - view port height).
This is a convenience method which interfaces with the Adjustable
objects which represent the state of the scrollbars.

Params:
  • p – the Point representing the position to scroll to
Throws:
/**
     * Scrolls to the specified position within the child component.
     * A call to this method is only valid if the scroll pane contains
     * a child and the specified position is within legal scrolling bounds
     * of the child.  Specifying a position outside of the legal scrolling
     * bounds of the child will scroll to the closest legal position.
     * Legal bounds are defined to be the rectangle:
     * x = 0, y = 0, width = (child width - view port width),
     * height = (child height - view port height).
     * This is a convenience method which interfaces with the Adjustable
     * objects which represent the state of the scrollbars.
     * @param p the Point representing the position to scroll to
     * @throws NullPointerException if {@code p} is {@code null}
     */
    public void setScrollPosition(Point p) {
        setScrollPosition(p.x, p.y);
    }

    
Returns the current x,y position within the child which is displayed
at the 0,0 location of the scrolled panel's view port.
This is a convenience method which interfaces with the adjustable
objects which represent the state of the scrollbars.

Throws:
Returns:the coordinate position for the current scroll position
/**
     * Returns the current x,y position within the child which is displayed
     * at the 0,0 location of the scrolled panel's view port.
     * This is a convenience method which interfaces with the adjustable
     * objects which represent the state of the scrollbars.
     * @return the coordinate position for the current scroll position
     * @throws NullPointerException if the scrollpane does not contain
     *     a child
     */
    @Transient
    public Point getScrollPosition() {
        synchronized (getTreeLock()) {
            if (getComponentCount()==0) {
                throw new NullPointerException("child is null");
            }
            return new Point(hAdjustable.getValue(), vAdjustable.getValue());
        }
    }

    
Sets the layout manager for this container.  This method is
overridden to prevent the layout mgr from being set.

Params:
  • mgr – the specified layout manager
/**
     * Sets the layout manager for this container.  This method is
     * overridden to prevent the layout mgr from being set.
     * @param mgr the specified layout manager
     */
    public final void setLayout(LayoutManager mgr) {
        throw new AWTError("ScrollPane controls layout");
    }

    
Lays out this container by resizing its child to its preferred size.
If the new preferred size of the child causes the current scroll
position to be invalid, the scroll position is set to the closest
valid position.

See Also:
  • validate.validate
/**
     * Lays out this container by resizing its child to its preferred size.
     * If the new preferred size of the child causes the current scroll
     * position to be invalid, the scroll position is set to the closest
     * valid position.
     *
     * @see Component#validate
     */
    public void doLayout() {
        layout();
    }

    
Determine the size to allocate the child component.
If the viewport area is bigger than the preferred size
of the child then the child is allocated enough
to fill the viewport, otherwise the child is given
it's preferred size.

/**
     * Determine the size to allocate the child component.
     * If the viewport area is bigger than the preferred size
     * of the child then the child is allocated enough
     * to fill the viewport, otherwise the child is given
     * it's preferred size.
     */
    Dimension calculateChildSize() {
        //
        // calculate the view size, accounting for border but not scrollbars
        // - don't use right/bottom insets since they vary depending
        //   on whether or not scrollbars were displayed on last resize
        //
        Dimension       size = getSize();
        Insets          insets = getInsets();
        int             viewWidth = size.width - insets.left*2;
        int             viewHeight = size.height - insets.top*2;

        //
        // determine whether or not horz or vert scrollbars will be displayed
        //
        boolean vbarOn;
        boolean hbarOn;
        Component child = getComponent(0);
        Dimension childSize = new Dimension(child.getPreferredSize());

        if (scrollbarDisplayPolicy == SCROLLBARS_AS_NEEDED) {
            vbarOn = childSize.height > viewHeight;
            hbarOn = childSize.width  > viewWidth;
        } else if (scrollbarDisplayPolicy == SCROLLBARS_ALWAYS) {
            vbarOn = hbarOn = true;
        } else { // SCROLLBARS_NEVER
            vbarOn = hbarOn = false;
        }

        //
        // adjust predicted view size to account for scrollbars
        //
        int vbarWidth = getVScrollbarWidth();
        int hbarHeight = getHScrollbarHeight();
        if (vbarOn) {
            viewWidth -= vbarWidth;
        }
        if(hbarOn) {
            viewHeight -= hbarHeight;
        }

        //
        // if child is smaller than view, size it up
        //
        if (childSize.width < viewWidth) {
            childSize.width = viewWidth;
        }
        if (childSize.height < viewHeight) {
            childSize.height = viewHeight;
        }

        return childSize;
    }

    
Deprecated:As of JDK version 1.1, replaced by doLayout().
/**
     * @deprecated As of JDK version 1.1,
     * replaced by {@code doLayout()}.
     */
    @Deprecated
    public void layout() {
        if (getComponentCount()==0) {
            return;
        }
        Component c = getComponent(0);
        Point p = getScrollPosition();
        Dimension cs = calculateChildSize();
        Dimension vs = getViewportSize();

        c.reshape(- p.x, - p.y, cs.width, cs.height);
        ScrollPanePeer peer = (ScrollPanePeer)this.peer;
        if (peer != null) {
            peer.childResized(cs.width, cs.height);
        }

        // update adjustables... the viewport size may have changed
        // with the scrollbars coming or going so the viewport size
        // is updated before the adjustables.
        vs = getViewportSize();
        hAdjustable.setSpan(0, cs.width, vs.width);
        vAdjustable.setSpan(0, cs.height, vs.height);
    }

    
Prints the component in this scroll pane.

Params:
  • g – the specified Graphics window
See Also:
/**
     * Prints the component in this scroll pane.
     * @param g the specified Graphics window
     * @see Component#print
     * @see Component#printAll
     */
    public void printComponents(Graphics g) {
        if (getComponentCount()==0) {
            return;
        }
        Component c = getComponent(0);
        Point p = c.getLocation();
        Dimension vs = getViewportSize();
        Insets i = getInsets();

        Graphics cg = g.create();
        try {
            cg.clipRect(i.left, i.top, vs.width, vs.height);
            cg.translate(p.x, p.y);
            c.printAll(cg);
        } finally {
            cg.dispose();
        }
    }

    
Creates the scroll pane's peer.

/**
     * Creates the scroll pane's peer.
     */
    public void addNotify() {
        synchronized (getTreeLock()) {

            int vAdjustableValue = 0;
            int hAdjustableValue = 0;

            // Bug 4124460. Save the current adjustable values,
            // so they can be restored after addnotify. Set the
            // adjustables to 0, to prevent crashes for possible
            // negative values.
            if (getComponentCount() > 0) {
                vAdjustableValue = vAdjustable.getValue();
                hAdjustableValue = hAdjustable.getValue();
                vAdjustable.setValue(0);
                hAdjustable.setValue(0);
            }

            if (peer == null)
                peer = getComponentFactory().createScrollPane(this);
            super.addNotify();

            // Bug 4124460. Restore the adjustable values.
            if (getComponentCount() > 0) {
                vAdjustable.setValue(vAdjustableValue);
                hAdjustable.setValue(hAdjustableValue);
            }
        }
    }

    
Returns a string representing the state of this ScrollPane. 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 null. 
Returns:the parameter string of this scroll pane
/**
     * Returns a string representing the state of this
     * {@code ScrollPane}. 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 the parameter string of this scroll pane
     */
    public String paramString() {
        String sdpStr;
        switch (scrollbarDisplayPolicy) {
            case SCROLLBARS_AS_NEEDED:
                sdpStr = "as-needed";
                break;
            case SCROLLBARS_ALWAYS:
                sdpStr = "always";
                break;
            case SCROLLBARS_NEVER:
                sdpStr = "never";
                break;
            default:
                sdpStr = "invalid display policy";
        }
        Point p = (getComponentCount()>0)? getScrollPosition() : new Point(0,0);
        Insets i = getInsets();
        return super.paramString()+",ScrollPosition=("+p.x+","+p.y+")"+
            ",Insets=("+i.top+","+i.left+","+i.bottom+","+i.right+")"+
            ",ScrollbarDisplayPolicy="+sdpStr+
        ",wheelScrollingEnabled="+isWheelScrollingEnabled();
    }

    void autoProcessMouseWheel(MouseWheelEvent e) {
        processMouseWheelEvent(e);
    }

    
Process mouse wheel events that are delivered to this ScrollPane by scrolling an appropriate amount. 
Note that if the event parameter is null the behavior is unspecified and may result in an exception. 
Params:
  • e –  the mouse wheel event
Since:1.4
/**
     * Process mouse wheel events that are delivered to this
     * {@code ScrollPane} by scrolling an appropriate amount.
     * <p>Note that if the event parameter is {@code null}
     * the behavior is unspecified and may result in an
     * exception.
     *
     * @param e  the mouse wheel event
     * @since 1.4
     */
    protected void processMouseWheelEvent(MouseWheelEvent e) {
        if (isWheelScrollingEnabled()) {
            ScrollPaneWheelScroller.handleWheelScrolling(this, e);
            e.consume();
        }
        super.processMouseWheelEvent(e);
    }

    
If wheel scrolling is enabled, we return true for MouseWheelEvents

Since:1.4
/**
     * If wheel scrolling is enabled, we return true for MouseWheelEvents
     * @since 1.4
     */
    protected boolean eventTypeEnabled(int type) {
        if (type == MouseEvent.MOUSE_WHEEL && isWheelScrollingEnabled()) {
            return true;
        }
        else {
            return super.eventTypeEnabled(type);
        }
    }

    
Enables/disables scrolling in response to movement of the mouse wheel.
Wheel scrolling is enabled by default.

Params:
  • handleWheel –  true if scrolling should be done automatically for a MouseWheelEvent, false otherwise.
See Also:
Since:1.4
/**
     * 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
     */
    public void setWheelScrollingEnabled(boolean handleWheel) {
        wheelScrollingEnabled = handleWheel;
    }

    
Indicates whether or not scrolling will take place in response to
the mouse wheel.  Wheel scrolling is enabled by default.

See Also:
Returns:true if the wheel scrolling enabled; otherwise false
Since:1.4
/**
     * Indicates whether or not scrolling will take place in response to
     * the mouse wheel.  Wheel scrolling is enabled by default.
     *
     * @return {@code true} if the wheel scrolling enabled;
     *         otherwise {@code false}
     *
     * @see #setWheelScrollingEnabled(boolean)
     * @since 1.4
     */
    public boolean isWheelScrollingEnabled() {
        return wheelScrollingEnabled;
    }


    
Writes default serializable fields to stream.

/**
     * Writes default serializable fields to stream.
     */
    private void writeObject(ObjectOutputStream s) throws IOException {
        // 4352819: We only need this degenerate writeObject to make
        // it safe for future versions of this class to write optional
        // data to the stream.
        s.defaultWriteObject();
    }

    
Reads default serializable fields to stream.

Throws:
  • HeadlessException – if GraphicsEnvironment.isHeadless() returns true
See Also:
/**
     * Reads default serializable fields to stream.
     * @exception HeadlessException if
     * {@code GraphicsEnvironment.isHeadless()} returns
     * {@code true}
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    private void readObject(ObjectInputStream s)
        throws ClassNotFoundException, IOException, HeadlessException
    {
        GraphicsEnvironment.checkHeadless();
        // 4352819: Gotcha!  Cannot use s.defaultReadObject here and
        // then continue with reading optional data.  Use GetField instead.
        ObjectInputStream.GetField f = s.readFields();

        // Old fields
        scrollbarDisplayPolicy = f.get("scrollbarDisplayPolicy",
                                       SCROLLBARS_AS_NEEDED);
        hAdjustable = (ScrollPaneAdjustable)f.get("hAdjustable", null);
        vAdjustable = (ScrollPaneAdjustable)f.get("vAdjustable", null);

        // Since 1.4
        wheelScrollingEnabled = f.get("wheelScrollingEnabled",
                                      defaultWheelScroll);

//      // Note to future maintainers
//      if (f.defaulted("wheelScrollingEnabled")) {
//          // We are reading pre-1.4 stream that doesn't have
//          // optional data, not even the TC_ENDBLOCKDATA marker.
//          // Reading anything after this point is unsafe as we will
//          // read unrelated objects further down the stream (4352819).
//      }
//      else {
//          // Reading data from 1.4 or later, it's ok to try to read
//          // optional data as OptionalDataException with eof == true
//          // will be correctly reported
//      }
    }

    class PeerFixer implements AdjustmentListener, java.io.Serializable
    {
        private static final long serialVersionUID = 1043664721353696630L;

        PeerFixer(ScrollPane scroller) {
            this.scroller = scroller;
        }

        
Invoked when the value of the adjustable has changed.

/**
         * Invoked when the value of the adjustable has changed.
         */
        @SuppressWarnings("deprecation")
        public void adjustmentValueChanged(AdjustmentEvent e) {
            Adjustable adj = e.getAdjustable();
            int value = e.getValue();
            ScrollPanePeer peer = (ScrollPanePeer) scroller.peer;
            if (peer != null) {
                peer.setValue(adj, value);
            }

            Component c = scroller.getComponent(0);
            switch(adj.getOrientation()) {
            case Adjustable.VERTICAL:
                c.move(c.getLocation().x, -(value));
                break;
            case Adjustable.HORIZONTAL:
                c.move(-(value), c.getLocation().y);
                break;
            default:
                throw new IllegalArgumentException("Illegal adjustable orientation");
            }
        }

        private ScrollPane scroller;
    }


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

    
Gets the AccessibleContext associated with this ScrollPane.
For scroll panes, the AccessibleContext takes the form of an
AccessibleAWTScrollPane.
A new AccessibleAWTScrollPane instance is created if necessary.

Returns:an AccessibleAWTScrollPane that serves as the
        AccessibleContext of this ScrollPane
Since:1.3
/**
     * Gets the AccessibleContext associated with this ScrollPane.
     * For scroll panes, the AccessibleContext takes the form of an
     * AccessibleAWTScrollPane.
     * A new AccessibleAWTScrollPane instance is created if necessary.
     *
     * @return an AccessibleAWTScrollPane that serves as the
     *         AccessibleContext of this ScrollPane
     * @since 1.3
     */
    public AccessibleContext getAccessibleContext() {
        if (accessibleContext == null) {
            accessibleContext = new AccessibleAWTScrollPane();
        }
        return accessibleContext;
    }

    
This class implements accessibility support for the ScrollPane class. It provides an implementation of the Java Accessibility API appropriate to scroll pane user-interface elements. 
Since:1.3
/**
     * This class implements accessibility support for the
     * {@code ScrollPane} class.  It provides an implementation of the
     * Java Accessibility API appropriate to scroll pane user-interface
     * elements.
     * @since 1.3
     */
    protected class AccessibleAWTScrollPane extends AccessibleAWTContainer
    {
        /*
         * JDK 1.3 serialVersionUID
         */
        private static final long serialVersionUID = 6100703663886637L;

        
Get the role of this object.

See Also:
Returns:an instance of AccessibleRole describing the role of the
object
/**
         * 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;
        }

    } // class AccessibleAWTScrollPane

}

/*
 * In JDK 1.1.1, the pkg private class java.awt.PeerFixer was moved to
 * become an inner class of ScrollPane, which broke serialization
 * for ScrollPane objects using JDK 1.1.
 * Instead of moving it back out here, which would break all JDK 1.1.x
 * releases, we keep PeerFixer in both places. Because of the scoping rules,
 * the PeerFixer that is used in ScrollPane will be the one that is the
 * inner class. This pkg private PeerFixer class below will only be used
 * if the Java 2 platform is used to deserialize ScrollPane objects that were serialized
 * using JDK1.1
 */
class PeerFixer implements AdjustmentListener, java.io.Serializable {
    /*
     * serialVersionUID
     */
    private static final long serialVersionUID = 7051237413532574756L;

    PeerFixer(ScrollPane scroller) {
        this.scroller = scroller;
    }

    
Invoked when the value of the adjustable has changed.

/**
     * Invoked when the value of the adjustable has changed.
     */
    @SuppressWarnings("deprecation")
    public void adjustmentValueChanged(AdjustmentEvent e) {
        Adjustable adj = e.getAdjustable();
        int value = e.getValue();
        ScrollPanePeer peer = (ScrollPanePeer) scroller.peer;
        if (peer != null) {
            peer.setValue(adj, value);
        }

        Component c = scroller.getComponent(0);
        switch(adj.getOrientation()) {
        case Adjustable.VERTICAL:
            c.move(c.getLocation().x, -(value));
            break;
        case Adjustable.HORIZONTAL:
            c.move(-(value), c.getLocation().y);
            break;
        default:
            throw new IllegalArgumentException("Illegal adjustable orientation");
        }
    }

    private ScrollPane scroller;
}