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Class com.sun.java.swing.JViewport

java.lang.Object
   |
   +----java.awt.Component
           |
           +----java.awt.Container
                   |
                   +----com.sun.java.swing.JComponent
                           |
                           +----com.sun.java.swing.JViewport

public class JViewport

extends JComponent

implements Accessible

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 Swing1.0 applications. It will not be possible to load serialized Swing1.0 objects with future releases of Swing. The JDK1.2 release of Swing will be the compatibility baseline for the serialized form of Swing objects.

See Also:

JScrollPane

backingStore

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.

backingStoreImage

The view image used for a backing store.

isViewSizeSet

True when the viewport dimensions have been determined.

lastPaintPosition

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

scrollUnderway

The scrollUnderway flag is used for components like JList.

JViewport()

Create a JViewPort

addChangeListener(ChangeListener)

Add a ChangeListener to the list that's notified each time the view's size, position, or the viewport's extent size has changed.

addImpl(Component, Object, int)

Sets the Viewport's one lightweight child, which can be null.

computeBlit(int, int, Point, Point, Dimension, Rectangle)

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.

createLayoutManager()

Subclassers can override this to install a different layout manager (or null) in the constructor.

createViewListener()

Create a listener for the view.

fireStateChanged()

getAccessibleContext()

Get the AccessibleContext associated with this JComponent

getExtentSize()

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

getInsets()

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

getView()

Returns the Viewport's one child or null.

getViewPosition()

Returns the view coordinates that appear in the upper left hand corner of the viewport, 0,0 if there's no view.

getViewRect()

Return a rectangle whose origin is getViewPosition and size is getExtentSize().

getViewSize()

If the view's size hasn't been explicitly set, return the preferred size, otherwise return the view's current size.

isBackingStoreEnabled()

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

isOptimizedDrawingEnabled()

The JViewport overrides the default implementation of this method (in JComponent) to return false.

paint(Graphics)

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.

remove(Component)

Removes the Viewport's one lightweight child.

removeChangeListener(ChangeListener)

Remove a ChangeListener from the list that's notified each time the views size, position, or the viewports extent size has changed.

repaint(long, int, int, int, int)

We always repaint in our parent coordinate system to make sure only one paint is performed by the RepaintManager.

scrollRectToVisible(Rectangle)

Overridden to scroll the view so that Rectangle within the view becomes visible.

setBackingStoreEnabled(boolean)

If true if this viewport will maintain an offscreen image of its contents.

setBorder(Border)

The viewport "scrolls" it's child (called the "view") by the normal parent/child clipping (typically the view is moved in the opposite direction of the scroll).

setBounds(int, int, int, int)

Sets the bounds of this viewport.

setExtentSize(Dimension)

Set the size of the visible part of the view using view coordinates.

setView(Component)

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

setViewPosition(Point)

Sets the view coordinates that appear in the upper left hand corner of the viewport, null if there's no view.

setViewSize(Dimension)

Sets the view coordinates that appear in the upper left hand corner of the viewport, and the size of the view.

toViewCoordinates(Dimension)

Convert a size in pixel coordinates to view coordinates.

toViewCoordinates(Point)

Convert a point in pixel coordinates to view coordinates.

 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 backingStore

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.

 protected transient Image backingStoreImage

The view image used for a backing store.

 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 optimised 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 Viewport class and have the JList manage this case by using setBackingStoreEnabled().

 public JViewport()

Create a JViewPort

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

Sets the Viewport'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.)

Parameters:

child - the Component ______________

constraints - the Object ______________

index - the int ______________

Overrides:

addImpl in class Container

See Also:

setView

 public void remove(Component child)

Removes the Viewport's one lightweight child.

Overrides:

remove in class Container

See Also:

setView

 public void scrollRectToVisible(Rectangle contentRect)

Overridden to scroll the view so that Rectangle within the view becomes visible.

Parameters:

contentRect - the Rectangle to display

Overrides:

scrollRectToVisible in class JComponent

 public final void setBorder(Border border)

The viewport "scrolls" it's 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.

Parameters:

border - the Border to set

Overrides:

setBorder in class JComponent

 public final Insets getInsets()

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

Returns:

new Insets(0, 0, 0, 0)

Overrides:

getInsets in class JComponent

See Also:

setBorder

 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.

Returns:

false

Overrides:

isOptimizedDrawingEnabled in class JComponent

 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 bunch of bits. (In case you were curious.)

Parameters:

g - the Graphics context within which to paint

Overrides:

paint in class JComponent

 public void setBounds(int x,
                       int y,
                       int w,
                       int h)

Sets the bounds of this viewport.

Parameters:

x - an int giving distance from left in pixels

y - an int giving distance from top in pixels

w - an int giving width in pixels

h - an int giving height in pixels

Overrides:

setBounds in class Component

See Also:

setBounds

 public boolean isBackingStoreEnabled()

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

 public void setBackingStoreEnabled(boolean x)

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.

 public Component getView()

Returns the Viewport's one child or null.

See Also:

setView

 public void setView(Component view)

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

See Also:

getView

 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

 public void setViewSize(Dimension newSize)

Sets the view coordinates that appear in the upper left hand corner of the viewport, and the size of the view.

Parameters:

newSize - a Dimension object specifying the size and location of the new view coordinates, or null if there is no view

 public Point getViewPosition()

Returns the view coordinates that appear in the upper left hand corner of the viewport, 0,0 if there's no view.

Returns:

a Point object giving the upper left coordinates

 public void setViewPosition(Point p)

Sets the view coordinates that appear in the upper left hand corner of the viewport, null if there's no view.

Parameters:

p - a Point object giving the upper left coordinates

 public Rectangle getViewRect()

Return 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.

 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.

 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

 public Dimension toViewCoordinates(Dimension size)

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

Parameters:

size - a Dimension object using pixel coordinates

Returns:

a Dimension object converted to view coordinates

 public Point toViewCoordinates(Point p)

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

Parameters:

p - a Point object using pixel coordinates

Returns:

a Point object converted to view coordinates

 public void setExtentSize(Dimension newExtent)

Set the size of the visible part of the view using view coordinates.

Parameters:

newExtent - a Dimension object specifying the size of the view

 protected JViewport. ViewListener createViewListener()

Create a listener for the view.

Returns:

a ViewListener

 protected LayoutManager createLayoutManager()

Subclassers can override this to install a different layout manager (or null) in the constructor. Returns a new JViewportLayout object.

Returns:

a LayoutManager

 public void addChangeListener(ChangeListener l)

Add a ChangeListener to the list that's notified each time the view's size, position, or the viewport's extent size has changed.

Parameters:

l - the ChangeListener to add

See Also:

removeChangeListener, setViewPosition, setViewSize, setExtentSize

 public void removeChangeListener(ChangeListener l)

Remove a ChangeListener from the list that's notified each time the views size, position, or the viewports extent size has changed.

Parameters:

l - the ChangeListener to remove

See Also:

addChangeListener

 protected void fireStateChanged()

 public void repaint(long tm,
                     int x,
                     int y,
                     int w,
                     int h)

We always repaint in our parent coordinate system to make sure only one paint is performed by the RepaintManager.

Parameters:

tm - maximum time in milliseconds before update

x - the x coordinate (pixels over from left)

y - the y coordinate (pixels down from top)

width - the width

height - the height

Overrides:

repaint in class JComponent

See Also:

update

 public AccessibleContext getAccessibleContext()

Get the AccessibleContext associated with this JComponent

Returns:

the AccessibleContext of this JComponent

Overrides:

getAccessibleContext in class JComponent

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