javax.swing
Class JViewport

java.lang.Object
  java.awt.Component
      java.awt.Container
          javax.swing.JComponent
              javax.swing.JViewport

All Implemented Interfaces:

ImageObserver, MenuContainer, Serializable, Accessible

public class JViewport
extends JComponent
implements Accessible

The "viewport" or "porthole" through which you see the underlying information. When you scroll, what moves is the viewport. It is like peering through a camera's viewfinder. Moving the viewfinder upwards brings new things into view at the top of the picture and loses things that were at the bottom.

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:

1. The view and parent view and checked to see if they are JComponents, if they aren't, stop and repaint the whole viewport.
2. If the viewport is obscured by an ancestor, stop and repaint the whole viewport.
3. Compute the region that will become visible, if it is as big as the viewport, stop and repaint the whole view region.
4. Obtain the ancestor Window's graphics and do a copyArea on the scrolled region.
5. Message the view to repaint the newly visible region.
6. 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.

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^TM has been added to the java.beans package. Please see XMLEncoder.

See Also:

JScrollPane

Nested Class Summary
protected  class	JViewport.AccessibleJViewport           This class implements accessibility support for the JViewport class.
protected  class	JViewport.ViewListener           A listener for the view.

 

Nested classes/interfaces inherited from class javax.swing.JComponent
JComponent.AccessibleJComponent

 

Nested classes/interfaces inherited from class java.awt.Container
Container.AccessibleAWTContainer

 

Nested classes/interfaces inherited from class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy

 

Field Summary
protected  boolean	backingStore           Deprecated. As of Java 2 platform v1.3
static int	BACKINGSTORE_SCROLL_MODE           Draws viewport contents into an offscreen image.
protected  Image	backingStoreImage           The view image used for a backing store.
static int	BLIT_SCROLL_MODE           Use graphics.copyArea to implement scrolling.
protected  boolean	isViewSizeSet           True when the viewport dimensions have been determined.
protected  Point	lastPaintPosition           The last viewPosition that we've painted, so we know how much of the backing store image is valid.
protected  boolean	scrollUnderway           The scrollUnderway flag is used for components like JList.
static int	SIMPLE_SCROLL_MODE           This mode uses the very simple method of redrawing the entire contents of the scrollpane each time it is scrolled.

 

Fields inherited from class javax.swing.JComponent
accessibleContext, listenerList, TOOL_TIP_TEXT_KEY, ui, UNDEFINED_CONDITION, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, WHEN_FOCUSED, WHEN_IN_FOCUSED_WINDOW

 

Fields inherited from class java.awt.Component
BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

 

Fields inherited from interface java.awt.image.ImageObserver
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH

 

Constructor Summary
JViewport()           Creates a JViewport.

 

Method Summary
void	addChangeListener(ChangeListener l)           Adds a ChangeListener to the list that is notified each time the view's size, position, or the viewport's extent size has changed.
protected  void	addImpl(Component child, Object constraints, int index)           Sets the JViewport's one lightweight child, which can be null.
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 contains oldLoc in the upper left hand corner and we're scrolling to newLoc.
protected  LayoutManager	createLayoutManager()           Subclassers can override this to install a different layout manager (or null) in the constructor.
protected  JViewport.ViewListener	createViewListener()           Creates a listener for the view.
protected  void	firePropertyChange(String propertyName, Object oldValue, Object newValue)           Notifies listeners of a property change.
protected  void	fireStateChanged()           Notifies all ChangeListeners when the views size, position, or the viewports extent size has changed.
AccessibleContext	getAccessibleContext()           Gets the AccessibleContext associated with this JViewport.
ChangeListener[]	getChangeListeners()           Returns an array of all the ChangeListeners added to this JViewport with addChangeListener().
Dimension	getExtentSize()           Returns the size of the visible part of the view in view coordinates.
Insets	getInsets()           Returns the insets (border) dimensions as (0,0,0,0), since borders are not supported on a JViewport.
Insets	getInsets(Insets insets)           Returns an Insets object containing this JViewports inset values.
int	getScrollMode()           Returns the current scrolling mode.
ViewportUI	getUI()           Returns the L&F object that renders this component.
String	getUIClassID()           Returns a string that specifies the name of the L&F class that renders this component.
Component	getView()           Returns the JViewport's one child or null.
Point	getViewPosition()           Returns the view coordinates that appear in the upper left hand corner of the viewport, or 0,0 if there's no view.
Rectangle	getViewRect()           Returns a rectangle whose origin is getViewPosition and size is getExtentSize.
Dimension	getViewSize()           If the view's size hasn't been explicitly set, return the preferred size, otherwise return the view's current size.
boolean	isBackingStoreEnabled()           Deprecated. As of Java 2 platform v1.3, replaced by getScrollMode().
boolean	isOptimizedDrawingEnabled()           The JViewport overrides the default implementation of this method (in JComponent) to return false.
void	paint(Graphics g)           Depending on whether the backingStore is 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  String	paramString()           Returns a string representation of this JViewport.
void	remove(Component child)           Removes the Viewports one lightweight child.
void	removeChangeListener(ChangeListener l)           Removes a ChangeListener from the list that's notified each time the views size, position, or the viewports extent size has changed.
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 the RepaintManager.
void	reshape(int x, int y, int w, int h)           Sets the bounds of this viewport.
void	scrollRectToVisible(Rectangle contentRect)           Scrolls the view so that Rectangle within the view becomes visible.
void	setBackingStoreEnabled(boolean enabled)           Deprecated. As of Java 2 platform v1.3, replaced by setScrollMode().
void	setBorder(Border border)           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).
void	setExtentSize(Dimension newExtent)           Sets the size of the visible part of the view using view coordinates.
void	setScrollMode(int mode)           Used to control the method of scrolling the viewport contents.
void	setUI(ViewportUI ui)           Sets the L&F object that renders this component.
void	setView(Component view)           Sets the JViewport's one lightweight child (view), which can be null.
void	setViewPosition(Point p)           Sets the view coordinates that appear in the upper left hand corner of the viewport, does nothing if there's no view.
void	setViewSize(Dimension newSize)           Sets the size of the view.
Dimension	toViewCoordinates(Dimension size)           Converts a size in pixel coordinates to view coordinates.
Point	toViewCoordinates(Point p)           Converts a point in pixel coordinates to view coordinates.
void	updateUI()           Resets the UI property to a value from the current look and feel.

 

Methods inherited from class javax.swing.JComponent

addAncestorListener, addNotify, addVetoableChangeListener, computeVisibleRect, contains, createToolTip, disable, enable, firePropertyChange, 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, 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, update

 

Methods inherited from 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, transferFocusBackward, transferFocusDownCycle, validate, validateTree

 

Methods inherited from 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, 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, getPeer, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getToolkit, getTreeLock, gotFocus, handleEvent, hasFocus, hide, 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, resize, resize, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setFocusable, setFocusTraversalKeysEnabled, setIgnoreRepaint, setLocale, setLocation, setLocation, setName, setSize, setSize, show, show, size, toString, transferFocus, transferFocusUpCycle

 

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

 

Field Detail

isViewSizeSet

protected boolean isViewSizeSet

True when the viewport dimensions have been determined. The default is false.

lastPaintPosition

protected Point lastPaintPosition

The last viewPosition that we've painted, so we know how much of the backing store image is valid.

backingStore

@Deprecated
protected boolean backingStore

Deprecated. As of Java 2 platform v1.3

True 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 is false.

See Also:

setScrollMode(int)

backingStoreImage

protected transient Image backingStoreImage

The view image used for a backing store.

scrollUnderway

protected boolean scrollUnderway

The scrollUnderway flag is used for components like JList. When the downarrow key is pressed on a JList and the selected cell is the last in the list, the scrollpane autoscrolls. 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 to setViewPosition(Point). When setBounds is called through other routes, the flag is off and the view repaints normally. Another approach would be to remove this from the JViewport class and have the JList manage this case by using setBackingStoreEnabled. The default is false.

BLIT_SCROLL_MODE

public static final int BLIT_SCROLL_MODE

Use graphics.copyArea to implement scrolling. This is the fastest for most applications.

Since:

1.3

See Also:

setScrollMode(int), Constant Field Values

BACKINGSTORE_SCROLL_MODE

public static final int BACKINGSTORE_SCROLL_MODE

Draws viewport contents into an offscreen image. This was previously the default mode for JTable. 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:

setScrollMode(int), Constant Field Values

SIMPLE_SCROLL_MODE

public static final int SIMPLE_SCROLL_MODE

This 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:

setScrollMode(int), Constant Field Values

JViewport

public JViewport()

Creates a JViewport.

getUI

public ViewportUI getUI()

Returns the L&F object that renders this component.

Returns:

a ViewportUI object

Since:

1.3

setUI

public void setUI(ViewportUI ui)

Sets the L&F object that renders this component.

Parameters:

ui - the ViewportUI L&F object

Since:

1.3

See Also:

UIDefaults.getUI(javax.swing.JComponent)

updateUI

public void updateUI()

Resets the UI property to a value from the current look and feel.

Overrides:

updateUI in class JComponent

See Also:

JComponent.updateUI()

getUIClassID

public String getUIClassID()

Returns a string that specifies the name of the L&F class that renders this component.

Overrides:

getUIClassID in class JComponent

Returns:

the string "ViewportUI"

See Also:

JComponent.getUIClassID(), UIDefaults.getUI(javax.swing.JComponent)

addImpl

protected void addImpl(Component child,
                       Object constraints,
                       int index)

Sets the JViewport's one lightweight child, which can be null. (Since there is only one child which occupies the entire viewport, the constraints and index arguments are ignored.)

Overrides:

addImpl in class Container

Parameters:

child - the lightweight child of the viewport

constraints - the constraints to be respected

index - the index

See Also:

setView(java.awt.Component)

remove

public void remove(Component child)

Removes the Viewports one lightweight child.

Overrides:

remove in class Container

Parameters:

child - the component to be removed

See Also:

setView(java.awt.Component)

scrollRectToVisible

public void scrollRectToVisible(Rectangle contentRect)

Scrolls the view so that Rectangle within the view becomes visible.

This attempts to validate the view before scrolling if the view is currently not valid - isValid returns 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 a Window or Applet.

Note that this method will not scroll outside of the valid viewport; for example, if contentRect is larger than the viewport, scrolling will be confined to the viewport's bounds.

Overrides:

scrollRectToVisible in class JComponent

Parameters:

contentRect - the Rectangle to display

See Also:

JComponent.isValidateRoot(), Component.isValid(), Component.getPeer()

setBorder

public final void setBorder(Border border)

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-null border, or non-zero insets, isn't supported, to prevent the geometry of this component from becoming complex enough to inhibit subclassing. To create a JViewport with a border, add it to a JPanel that has a border.

Note: If border is non-null, this method will throw an exception as borders are not supported on a JViewPort.

Overrides:

setBorder in class JComponent

Parameters:

border - the Border to set

Throws:

IllegalArgumentException - this method is not implemented

See Also:

Border, CompoundBorder

getInsets

public final Insets getInsets()

Returns the insets (border) dimensions as (0,0,0,0), since borders are not supported on a JViewport.

Overrides:

getInsets in class JComponent

Returns:

a Rectange of zero dimension and zero origin

See Also:

setBorder(javax.swing.border.Border)

getInsets

public final Insets getInsets(Insets insets)

Returns an Insets object containing this JViewports inset values. The passed-in Insets object will be reinitialized, and all existing values within this object are overwritten.

Overrides:

getInsets in class JComponent

Parameters:

insets - the Insets object which can be reused

Returns:

this viewports inset values

See Also:

getInsets()

isOptimizedDrawingEnabled

public boolean isOptimizedDrawingEnabled()

The JViewport overrides the default implementation of this method (in JComponent) to return false. This ensures that the drawing machinery will call the Viewport's paint implementation rather than messaging the JViewport's children directly.

Overrides:

isOptimizedDrawingEnabled in class JComponent

Returns:

false

paint

public void paint(Graphics g)

Depending on whether the backingStore is 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:

paint in class JComponent

Parameters:

g - the Graphics context within which to paint

See Also:

JComponent.paintComponent(java.awt.Graphics), JComponent.paintBorder(java.awt.Graphics), JComponent.paintChildren(java.awt.Graphics), JComponent.getComponentGraphics(java.awt.Graphics), JComponent.repaint(long, int, int, int, int)

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 a StateChanged event.

Overrides:

reshape in class JComponent

Parameters:

x - left edge of the origin

y - top edge of the origin

w - width in pixels

h - height in pixels

See Also:

JComponent.reshape(int, int, int, int)

setScrollMode

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:

BLIT_SCROLL_MODE, BACKINGSTORE_SCROLL_MODE, SIMPLE_SCROLL_MODE

getScrollMode

public int getScrollMode()

Returns the current scrolling mode.

Returns:

the scrollMode property

Since:

1.3

See Also:

setScrollMode(int)

isBackingStoreEnabled

@Deprecated
public boolean isBackingStoreEnabled()

Deprecated. As of Java 2 platform v1.3, replaced by getScrollMode().

Returns true if this viewport is maintaining an offscreen image of its contents.

Returns:

true if scrollMode is BACKINGSTORE_SCROLL_MODE

setBackingStoreEnabled

@Deprecated
public void setBackingStoreEnabled(boolean enabled)

Deprecated. As of Java 2 platform v1.3, replaced by setScrollMode().

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 the viewPosition. Rather than repainting the entire viewport we use Graphics.copyArea to effect some of the scroll.

Parameters:

enabled - if true, maintain an offscreen backing store

getView

public Component getView()

Returns the JViewport's one child or null.

Returns:

the viewports child, or null if none exists

See Also:

setView(java.awt.Component)

setView

public void setView(Component view)

Sets the JViewport's one lightweight child (view), which can be null.

Parameters:

view - the viewport's new lightweight child

See Also:

getView()

getViewSize

public Dimension 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 Dimension object specifying the size of the view

setViewSize

public void setViewSize(Dimension newSize)

Sets the size of the view. A state changed event will be fired.

Parameters:

newSize - a Dimension object specifying the new size of the view

getViewPosition

public Point 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 Point object giving the upper left coordinates

setViewPosition

public void setViewPosition(Point p)

Sets the view coordinates that appear in the upper left hand corner of the viewport, does nothing if there's no view.

Parameters:

p - a Point object giving the upper left coordinates

getViewRect

public Rectangle getViewRect()

Returns a rectangle whose origin is getViewPosition and size is getExtentSize. This is the visible part of the view, in view coordinates.

Returns:

a Rectangle giving 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 contains oldLoc in the upper left hand corner and we're scrolling to newLoc. The parameters are modified to return the values required for the blit.

Parameters:

dx - the horizontal delta

dy - the vertical delta

blitFrom - the Point we're blitting from

blitTo - the Point we're blitting to

blitSize - the Dimension of the area to blit

blitPaint - the area to blit

Returns:

true if the parameters are modified and we're ready to blit; false otherwise

getExtentSize

public Dimension getExtentSize()

Returns the size of the visible part of the view in view coordinates.

Returns:

a Dimension object giving the size of the view

toViewCoordinates

public Dimension toViewCoordinates(Dimension size)

Converts a size in pixel coordinates to view coordinates. Subclasses of viewport that support "logical coordinates" will override this method.

Parameters:</