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.
  In general this approach is much faster. Compared to the backing store approach this avoids the overhead of maintaining an offscreen buffer and having to do two `copyArea`s. 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 JavaBeansTM has been added to the `java.beans` package. Please see `XMLEncoder`.

  See Also:
    `JScrollPane`

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `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

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `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

    Constructors
    Constructor and Description
    `JViewport()` Creates a `JViewport`.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `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 `ChangeListener`s 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 `JViewport`s 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.
    `protected boolean` | `isPaintingOrigin()` Returns true if scroll mode is a `BACKINGSTORE_SCROLL_MODE` to cause painting to originate from `JViewport`, or one of its ancestors.
    `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 `Viewport`s 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, 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, 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, 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, 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, transferFocusBackward, 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

  - ### Constructor Detail

    - #### JViewport

          public JViewport()

      Creates a `JViewport`.

  - ### Method Detail

    - #### 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 `Viewport`s 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 `JViewport`s 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

    - #### isPaintingOrigin

          protected boolean isPaintingOrigin()

      Returns true if scroll mode is a `BACKINGSTORE_SCROLL_MODE` to cause painting to originate from `JViewport`, or one of its ancestors. Otherwise returns `false`.
      Overrides:
        `isPaintingOrigin` in class `JComponent`
      Returns:
        true if if scroll mode is a `BACKINGSTORE_SCROLL_MODE`.
      See Also:
        `JComponent.isPaintingOrigin()`

    - #### 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:
        `size` - a `Dimension` object using pixel coordinates
      Returns:
        a `Dimension` object converted to view coordinates

    - #### toViewCoordinates

          public Point toViewCoordinates(Point p)

      Converts 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

    - #### setExtentSize

          public void setExtentSize(Dimension newExtent)

      Sets the size of the visible part of the view using view coordinates.
      Parameters:
        `newExtent` - a `Dimension` object specifying the size of the view

    - #### createViewListener

          protected JViewport.ViewListener createViewListener()

      Creates a listener for the view.
      Returns:
        a `ViewListener`

    - #### createLayoutManager

          protected LayoutManager createLayoutManager()

      Subclassers can override this to install a different layout manager (or `null`) in the constructor. Returns the `LayoutManager` to install on the `JViewport`.
      Returns:
        a `LayoutManager`

    - #### addChangeListener

          public 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.
      Parameters:
        `l` - the `ChangeListener` to add
      See Also:
        `removeChangeListener(javax.swing.event.ChangeListener)`, `setViewPosition(java.awt.Point)`, `setViewSize(java.awt.Dimension)`, `setExtentSize(java.awt.Dimension)`

    - #### removeChangeListener

          public 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.
      Parameters:
        `l` - the `ChangeListener` to remove
      See Also:
        `addChangeListener(javax.swing.event.ChangeListener)`

    - #### getChangeListeners

          public ChangeListener[] getChangeListeners()

      Returns an array of all the `ChangeListener`s added to this JViewport with addChangeListener().
      Returns:
        all of the `ChangeListener`s added or an empty array if no listeners have been added
      Since:
        1.4

    - #### fireStateChanged

          protected void fireStateChanged()

      Notifies all `ChangeListeners` when the views size, position, or the viewports extent size has changed.
      See Also:
        `addChangeListener(javax.swing.event.ChangeListener)`, `removeChangeListener(javax.swing.event.ChangeListener)`, `EventListenerList`

    - #### 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 the `RepaintManager`.
      Overrides:
        `repaint` in class `JComponent`
      Parameters:
        `tm` - maximum time in milliseconds before update
        `x` - the `x` coordinate (pixels over from left)
        `y` - the `y` coordinate (pixels down from top)
        `w` - the width
        `h` - the height
      See Also:
        `Component.update(java.awt.Graphics)`

    - #### paramString

          protected String paramString()

      Returns a string representation of this `JViewport`. 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`.
      Overrides:
        `paramString` in class `JComponent`
      Returns:
        a string representation of this `JViewport`

    - #### firePropertyChange

          protected void firePropertyChange(String propertyName,
                                Object oldValue,
                                Object newValue)

      Notifies listeners of a property change. This is subclassed to update the `windowBlit` property. (The `putClientProperty` property is final).
      Overrides:
        `firePropertyChange` in class `Component`
      Parameters:
        `propertyName` - a string containing the property name
        `oldValue` - the old value of the property
        `newValue` - the new value of the property

    - #### getAccessibleContext

          public AccessibleContext 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:
        `getAccessibleContext` in interface `Accessible`
      Overrides:
        `getAccessibleContext` in class `JComponent`
      Returns:
        an AccessibleJViewport that serves as the AccessibleContext of this JViewport

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