Class JViewport
- All Implemented Interfaces:
ImageObserver,MenuContainer,Serializable,Accessible
By default, JViewport is opaque. To change this, use the
setOpaque method.
NOTE:We have implemented a faster scrolling algorithm that does not require a buffer to draw in. The algorithm works as follows:
- The view and parent view are checked to see if they are
JComponents, if they aren't, stop and repaint the whole viewport. - If the viewport is obscured by an ancestor, stop and repaint the whole viewport.
- Compute the region that will become visible, if it is as big as the viewport, stop and repaint the whole view region.
- Obtain the ancestor
Window's graphics and do acopyAreaon the scrolled region. - Message the view to repaint the newly visible region.
- The next time paint is invoked on the viewport, if the clip region is smaller than the viewport size a timer is kicked off to repaint the whole region.
copyAreas.
Compared to the non backing store case this
approach will greatly reduce the painted region.
This approach can cause slower times than the backing store approach when the viewport is obscured by another window, or partially offscreen. When another window obscures the viewport the copyArea will copy garbage and a paint event will be generated by the system to inform us we need to paint the newly exposed region. The only way to handle this is to repaint the whole viewport, which can cause slower performance than the backing store case. In most applications very rarely will the user be scrolling while the viewport is obscured by another window or offscreen, so this optimization is usually worth the performance hit when obscured.
Warning: Swing is not thread safe. For more information see Swing's Threading Policy.
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 java.beans package.
Please see XMLEncoder.
- Since:
- 1.2
- See Also:
-
Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionprotected classThis class implements accessibility support for theJViewportclass.protected classA listener for the view.Nested classes/interfaces declared in class javax.swing.JComponent
JComponent.AccessibleJComponentNested classes/interfaces declared in class java.awt.Container
Container.AccessibleAWTContainerNested classes/interfaces declared in class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy -
Field Summary
FieldsModifier and TypeFieldDescriptionprotected booleanDeprecated.As of Java 2 platform v1.3static final intDraws viewport contents into an offscreen image.protected ImageThe view image used for a backing store.static final intUsegraphics.copyAreato implement scrolling.protected booleanTrue when the viewport dimensions have been determined.protected PointThe lastviewPositionthat we've painted, so we know how much of the backing store image is valid.protected booleanThescrollUnderwayflag is used for components likeJList.static final intThis mode uses the very simple method of redrawing the entire contents of the scrollpane each time it is scrolled.Fields declared in class javax.swing.JComponent
listenerList, TOOL_TIP_TEXT_KEY, ui, UNDEFINED_CONDITION, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, WHEN_FOCUSED, WHEN_IN_FOCUSED_WINDOWFields declared in class java.awt.Component
accessibleContext, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENTFields declared in interface java.awt.image.ImageObserver
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoidAdds aChangeListenerto the list that is notified each time the view's size, position, or the viewport's extent size has changed.protected voidSets theJViewport's one lightweight child, which can benull.protected booleancomputeBlit(int dx, int dy, Point blitFrom, Point blitTo, Dimension blitSize, Rectangle blitPaint) Computes the parameters for a blit where the backing store image currently containsoldLocin the upper left hand corner and we're scrolling tonewLoc.protected LayoutManagerSubclassers can override this to install a different layout manager (ornull) in the constructor.protected JViewport.ViewListenerCreates a listener for the view.protected voidfirePropertyChange(String propertyName, Object oldValue, Object newValue) Notifies listeners of a property change.protected voidNotifies allChangeListenerswhen the views size, position, or the viewports extent size has changed.Gets the AccessibleContext associated with this JViewport.Returns an array of all theChangeListeners added to this JViewport with addChangeListener().Returns the size of the visible part of the view in view coordinates.final InsetsReturns the insets (border) dimensions as (0,0,0,0), since borders are not supported on aJViewport.final InsetsReturns anInsetsobject containing thisJViewports inset values.intReturns the current scrolling mode.getUI()Returns the L&F object that renders this component.Returns a string that specifies the name of the L&F class that renders this component.getView()Returns theJViewport's one child ornull.Returns the view coordinates that appear in the upper left hand corner of the viewport, or 0,0 if there's no view.Returns a rectangle whose origin isgetViewPositionand size isgetExtentSize.If the view's size hasn't been explicitly set, return the preferred size, otherwise return the view's current size.booleanDeprecated.As of Java 2 platform v1.3, replaced bygetScrollMode().booleanTheJViewportoverrides the default implementation of this method (inJComponent) to return false.protected booleanReturns true if scroll mode is aBACKINGSTORE_SCROLL_MODEto cause painting to originate fromJViewport, or one of its ancestors.voidDepending on whether thebackingStoreis enabled, either paint the image through the backing store or paint just the recently exposed part, using the backing store to "blit" the remainder.protected StringReturns a string representation of thisJViewport.voidRemoves theViewports one lightweight child.voidRemoves aChangeListenerfrom the list that's notified each time the views size, position, or the viewports extent size has changed.voidrepaint(long tm, int x, int y, int w, int h) Always repaint in the parents coordinate system to make sure only one paint is performed by theRepaintManager.voidreshape(int x, int y, int w, int h) Sets the bounds of this viewport.voidscrollRectToVisible(Rectangle contentRect) Scrolls the view so thatRectanglewithin the view becomes visible.voidsetBackingStoreEnabled(boolean enabled) Deprecated.As of Java 2 platform v1.3, replaced bysetScrollMode().final voidThe viewport "scrolls" its child (called the "view") by the normal parent/child clipping (typically the view is moved in the opposite direction of the scroll).voidsetExtentSize(Dimension newExtent) Sets the size of the visible part of the view using view coordinates.voidsetScrollMode(int mode) Used to control the method of scrolling the viewport contents.voidsetUI(ViewportUI ui) Sets the L&F object that renders this component.voidSets theJViewport's one lightweight child (view), which can benull.voidSets the view coordinates that appear in the upper left hand corner of the viewport, does nothing if there's no view.voidsetViewSize(Dimension newSize) Sets the size of the view.toViewCoordinates(Dimension size) Converts a size in pixel coordinates to view coordinates.Converts a point in pixel coordinates to view coordinates.voidupdateUI()Resets the UI property to a value from the current look and feel.Methods declared in class javax.swing.JComponent
addAncestorListener, addNotify, addVetoableChangeListener, computeVisibleRect, contains, createToolTip, disable, enable, firePropertyChange, firePropertyChange, fireVetoableChange, getActionForKeyStroke, getActionMap, getAlignmentX, getAlignmentY, getAncestorListeners, getAutoscrolls, getBaseline, getBaselineResizeBehavior, getBorder, getBounds, getClientProperty, getComponentGraphics, getComponentPopupMenu, getConditionForKeyStroke, getDebugGraphicsOptions, getDefaultLocale, getFontMetrics, getGraphics, getHeight, getInheritsPopupMenu, getInputMap, getInputMap, getInputVerifier, getListeners, getLocation, getMaximumSize, getMinimumSize, getNextFocusableComponent, getPopupLocation, getPreferredSize, getRegisteredKeyStrokes, getRootPane, getSize, getToolTipLocation, getToolTipText, getToolTipText, getTopLevelAncestor, getTransferHandler, getVerifyInputWhenFocusTarget, getVetoableChangeListeners, getVisibleRect, getWidth, getX, getY, grabFocus, hide, isDoubleBuffered, isLightweightComponent, isManagingFocus, isOpaque, isPaintingForPrint, isPaintingTile, isRequestFocusEnabled, isValidateRoot, paintBorder, paintChildren, paintComponent, paintImmediately, paintImmediately, print, printAll, printBorder, printChildren, printComponent, processComponentKeyEvent, processKeyBinding, processKeyEvent, processMouseEvent, processMouseMotionEvent, putClientProperty, registerKeyboardAction, registerKeyboardAction, removeAncestorListener, removeNotify, removeVetoableChangeListener, repaint, requestDefaultFocus, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, resetKeyboardActions, revalidate, setActionMap, setAlignmentX, setAlignmentY, setAutoscrolls, setBackground, setComponentPopupMenu, setDebugGraphicsOptions, setDefaultLocale, setDoubleBuffered, setEnabled, setFocusTraversalKeys, setFont, setForeground, setInheritsPopupMenu, setInputMap, setInputVerifier, setMaximumSize, setMinimumSize, setNextFocusableComponent, setOpaque, setPreferredSize, setRequestFocusEnabled, setToolTipText, setTransferHandler, setUI, setVerifyInputWhenFocusTarget, setVisible, unregisterKeyboardAction, updateMethods declared in class java.awt.Container
add, add, add, add, add, addContainerListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, countComponents, deliverEvent, doLayout, findComponentAt, findComponentAt, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents, getComponentZOrder, getContainerListeners, getFocusTraversalKeys, getFocusTraversalPolicy, getLayout, getMousePosition, insets, invalidate, isAncestorOf, isFocusCycleRoot, isFocusCycleRoot, isFocusTraversalPolicyProvider, isFocusTraversalPolicySet, layout, list, list, locate, minimumSize, paintComponents, preferredSize, printComponents, processContainerEvent, processEvent, remove, removeAll, removeContainerListener, setComponentZOrder, setFocusCycleRoot, setFocusTraversalPolicy, setFocusTraversalPolicyProvider, setLayout, transferFocusDownCycle, validate, validateTreeMethods declared in class java.awt.Component
action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, bounds, checkImage, checkImage, coalesceEvents, contains, createImage, createImage, createVolatileImage, createVolatileImage, disableEvents, dispatchEvent, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getBackground, getBounds, getColorModel, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeysEnabled, getFont, getForeground, getGraphicsConfiguration, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocationOnScreen, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getToolkit, getTreeLock, gotFocus, handleEvent, hasFocus, imageUpdate, inside, isBackgroundSet, isCursorSet, isDisplayable, isEnabled, isFocusable, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, requestFocus, requestFocus, requestFocusInWindow, resize, resize, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setFocusable, setFocusTraversalKeysEnabled, setIgnoreRepaint, setLocale, setLocation, setLocation, setMixingCutoutShape, setName, setSize, setSize, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle
-
Field Details
-
isViewSizeSet
protected boolean isViewSizeSetTrue when the viewport dimensions have been determined. The default is false. -
lastPaintPosition
The lastviewPositionthat we've painted, so we know how much of the backing store image is valid. -
backingStore
Deprecated.As of Java 2 platform v1.3True when this viewport is maintaining an offscreen image of its contents, so that some scrolling can take place using fast "bit-blit" operations instead of by accessing the view object to construct the display. The default isfalse.- See Also:
-
backingStoreImage
The view image used for a backing store. -
scrollUnderway
protected boolean scrollUnderwayThescrollUnderwayflag is used for components likeJList. When the downarrow key is pressed on aJListand the selected cell is the last in the list, thescrollpaneautoscrolls. Here, the old selected cell needs repainting and so we need a flag to make the viewport do the optimized painting only when there is an explicit call tosetViewPosition(Point). WhensetBoundsis called through other routes, the flag is off and the view repaints normally. Another approach would be to remove this from theJViewportclass and have theJListmanage this case by usingsetBackingStoreEnabled. The default isfalse. -
BLIT_SCROLL_MODE
public static final int BLIT_SCROLL_MODEUsegraphics.copyAreato implement scrolling. This is the fastest for most applications.- Since:
- 1.3
- See Also:
-
BACKINGSTORE_SCROLL_MODE
public static final int BACKINGSTORE_SCROLL_MODEDraws viewport contents into an offscreen image. This was previously the default mode forJTable. This mode may offer advantages over "blit mode" in some cases, but it requires a large chunk of extra RAM.- Since:
- 1.3
- See Also:
-
SIMPLE_SCROLL_MODE
public static final int SIMPLE_SCROLL_MODEThis mode uses the very simple method of redrawing the entire contents of the scrollpane each time it is scrolled. This was the default behavior in Swing 1.0 and Swing 1.1. Either of the other two options will provide better performance in most cases.- Since:
- 1.3
- See Also:
-
-
Constructor Details
-
JViewport
public JViewport()Creates aJViewport.
-
-
Method Details
-
getUI
Returns the L&F object that renders this component.- Overrides:
getUIin classJComponent- Returns:
- a
ViewportUIobject - Since:
- 1.3
-
setUI
@BeanProperty(hidden=true, visualUpdate=true, description="The UI object that implements the Component's LookAndFeel.") public void setUI(ViewportUI ui) Sets the L&F object that renders this component.- Parameters:
ui- theViewportUIL&F object- Since:
- 1.3
- See Also:
-
updateUI
public void updateUI()Resets the UI property to a value from the current look and feel.- Overrides:
updateUIin classJComponent- See Also:
-
getUIClassID
Returns a string that specifies the name of the L&F class that renders this component.- Overrides:
getUIClassIDin classJComponent- Returns:
- the string "ViewportUI"
- See Also:
-
addImpl
Sets theJViewport's one lightweight child, which can benull. (Since there is only one child which occupies the entire viewport, theconstraintsandindexarguments are ignored.) -
remove
-
scrollRectToVisible
Scrolls the view so thatRectanglewithin the view becomes visible.This attempts to validate the view before scrolling if the view is currently not valid -
isValidreturns false. To avoid excessive validation when the containment hierarchy is being created this will not validate if one of the ancestors does not have a peer, or there is no validate root ancestor, or one of the ancestors is not aWindoworApplet.Note that this method will not scroll outside of the valid viewport; for example, if
contentRectis larger than the viewport, scrolling will be confined to the viewport's bounds.- Overrides:
scrollRectToVisiblein classJComponent- Parameters:
contentRect- theRectangleto display- See Also:
-
setBorder
The viewport "scrolls" its child (called the "view") by the normal parent/child clipping (typically the view is moved in the opposite direction of the scroll). A non-nullborder, or non-zero insets, isn't supported, to prevent the geometry of this component from becoming complex enough to inhibit subclassing. To create aJViewportwith a border, add it to aJPanelthat has a border.Note: If
borderis non-null, this method will throw an exception as borders are not supported on aJViewPort.- Overrides:
setBorderin classJComponent- Parameters:
border- theBorderto set- Throws:
IllegalArgumentException- this method is not implemented- See Also:
-
getInsets
Returns the insets (border) dimensions as (0,0,0,0), since borders are not supported on aJViewport.- Overrides:
getInsetsin classJComponent- Returns:
- a
Rectangleof zero dimension and zero origin - See Also:
-
getInsets
Returns anInsetsobject containing thisJViewports inset values. The passed-inInsetsobject will be reinitialized, and all existing values within this object are overwritten.- Overrides:
getInsetsin classJComponent- Parameters:
insets- theInsetsobject which can be reused- Returns:
- this viewports inset values
- See Also:
-
isOptimizedDrawingEnabled
public boolean isOptimizedDrawingEnabled()TheJViewportoverrides the default implementation of this method (inJComponent) to return false. This ensures that the drawing machinery will call theViewport'spaintimplementation rather than messaging theJViewport's children directly.- Overrides:
isOptimizedDrawingEnabledin classJComponent- Returns:
- false
-
isPaintingOrigin
protected boolean isPaintingOrigin()Returns true if scroll mode is aBACKINGSTORE_SCROLL_MODEto cause painting to originate fromJViewport, or one of its ancestors. Otherwise returnsfalse.- Overrides:
isPaintingOriginin classJComponent- Returns:
- true if scroll mode is a
BACKINGSTORE_SCROLL_MODE. - See Also:
-
paint
Depending on whether thebackingStoreis enabled, either paint the image through the backing store or paint just the recently exposed part, using the backing store to "blit" the remainder.The term "blit" is the pronounced version of the PDP-10 BLT (BLock Transfer) instruction, which copied a block of bits. (In case you were curious.)
- Overrides:
paintin classJComponent- Parameters:
g- theGraphicscontext within which to paint- See Also:
-
reshape
public void reshape(int x, int y, int w, int h) Sets the bounds of this viewport. If the viewport's width or height has changed, fire aStateChangedevent.- Overrides:
reshapein classJComponent- Parameters:
x- left edge of the originy- top edge of the originw- width in pixelsh- height in pixels- See Also:
-
setScrollMode
@BeanProperty(bound=false, enumerationValues={"JViewport.BLIT_SCROLL_MODE","JViewport.BACKINGSTORE_SCROLL_MODE","JViewport.SIMPLE_SCROLL_MODE"}, description="Method of moving contents for incremental scrolls.") public void setScrollMode(int mode) Used to control the method of scrolling the viewport contents. You may want to change this mode to get maximum performance for your use case.- Parameters:
mode- one of the following values:- JViewport.BLIT_SCROLL_MODE
- JViewport.BACKINGSTORE_SCROLL_MODE
- JViewport.SIMPLE_SCROLL_MODE
- Since:
- 1.3
- See Also:
-
getScrollMode
public int getScrollMode()Returns the current scrolling mode.- Returns:
- the
scrollModeproperty - Since:
- 1.3
- See Also:
-
isBackingStoreEnabled
Deprecated.As of Java 2 platform v1.3, replaced bygetScrollMode().Returnstrueif this viewport is maintaining an offscreen image of its contents.- Returns:
trueifscrollModeisBACKINGSTORE_SCROLL_MODE
-
setBackingStoreEnabled
Deprecated.As of Java 2 platform v1.3, replaced bysetScrollMode().If true if this viewport will maintain an offscreen image of its contents. The image is used to reduce the cost of small one dimensional changes to theviewPosition. Rather than repainting the entire viewport we useGraphics.copyAreato effect some of the scroll.- Parameters:
enabled- if true, maintain an offscreen backing store
-
getView
Returns theJViewport's one child ornull.- Returns:
- the viewports child, or
nullif none exists - See Also:
-
setView
Sets theJViewport's one lightweight child (view), which can benull.- Parameters:
view- the viewport's new lightweight child- See Also:
-
getViewSize
If the view's size hasn't been explicitly set, return the preferred size, otherwise return the view's current size. If there is no view, return 0,0.- Returns:
- a
Dimensionobject specifying the size of the view
-
setViewSize
Sets the size of the view. A state changed event will be fired.- Parameters:
newSize- aDimensionobject specifying the new size of the view
-
getViewPosition
Returns the view coordinates that appear in the upper left hand corner of the viewport, or 0,0 if there's no view.- Returns:
- a
Pointobject giving the upper left coordinates
-
setViewPosition
Sets the view coordinates that appear in the upper left hand corner of the viewport, does nothing if there's no view.- Parameters:
p- aPointobject giving the upper left coordinates
-
getViewRect
Returns a rectangle whose origin isgetViewPositionand size isgetExtentSize. This is the visible part of the view, in view coordinates.- Returns:
- a
Rectanglegiving the visible part of the view using view coordinates.
-
computeBlit
protected boolean computeBlit(int dx, int dy, Point blitFrom, Point blitTo, Dimension blitSize, Rectangle blitPaint) Computes the parameters for a blit where the backing store image currently containsoldLocin the upper left hand corner and we're scrolling tonewLoc. The parameters are modified to return the values required for the blit.- Parameters:
dx- the horizontal deltady- the vertical deltablitFrom- thePointwe're blitting fromblitTo- thePointwe're blitting toblitSize- theDimensionof the area to blitblitPaint- the area to blit- Returns:
- true if the parameters are modified and we're ready to blit; false otherwise
-
getExtentSize
Returns the size of the visible part of the view in view coordinates.- Returns:
- a
Dimensionobject giving the size of the view
-
toViewCoordinates
Converts a size in pixel coordinates to view coordinates. Subclasses of viewport that support "logical coordinates" will override this method.- Parameters:
size- aDimensionobject using pixel coordinates- Returns:
- a
Dimensionobject converted to view coordinates
-
toViewCoordinates
-
setExtentSize
Sets the size of the visible part of the view using view coordinates.- Parameters:
newExtent- aDimensionobject specifying the size of the view
-
createViewListener
Creates a listener for the view.- Returns:
- a
ViewListener
-
createLayoutManager
Subclassers can override this to install a different layout manager (ornull) in the constructor. Returns theLayoutManagerto install on theJViewport.- Returns:
- a
LayoutManager
-
addChangeListener
Adds aChangeListenerto the list that is notified each time the view's size, position, or the viewport's extent size has changed.- Parameters:
l- theChangeListenerto add- See Also:
-
removeChangeListener
Removes aChangeListenerfrom the list that's notified each time the views size, position, or the viewports extent size has changed.- Parameters:
l- theChangeListenerto remove- See Also:
-
getChangeListeners
Returns an array of all theChangeListeners added to this JViewport with addChangeListener().- Returns:
- all of the
ChangeListeners added or an empty array if no listeners have been added - Since:
- 1.4
-
fireStateChanged
protected void fireStateChanged()Notifies allChangeListenerswhen the views size, position, or the viewports extent size has changed.- See Also:
-
repaint
public void repaint(long tm, int x, int y, int w, int h) Always repaint in the parents coordinate system to make sure only one paint is performed by theRepaintManager.- Overrides:
repaintin classJComponent- Parameters:
tm- maximum time in milliseconds before updatex- thexcoordinate (pixels over from left)y- theycoordinate (pixels down from top)w- the widthh- the height- See Also:
-
paramString
Returns a string representation of thisJViewport. 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 benull.- Overrides:
paramStringin classJComponent- Returns:
- a string representation of this
JViewport
-
firePropertyChange
Notifies listeners of a property change. This is subclassed to update thewindowBlitproperty. (TheputClientPropertyproperty is final).- Overrides:
firePropertyChangein classComponent- Parameters:
propertyName- a string containing the property nameoldValue- the old value of the propertynewValue- the new value of the property
-
getAccessibleContext
Gets the AccessibleContext associated with this JViewport. For viewports, the AccessibleContext takes the form of an AccessibleJViewport. A new AccessibleJViewport instance is created if necessary.- Specified by:
getAccessibleContextin interfaceAccessible- Overrides:
getAccessibleContextin classComponent- Returns:
- an AccessibleJViewport that serves as the AccessibleContext of this JViewport
-