JViewport

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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
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:

The view and parent view and 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 a copyArea on 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.

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 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: 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 , Serialized Form

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.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 `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.
`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 , getBorder , getBounds , getClientProperty`

javax.swing Class JViewport

javax.swing
Class JViewport