Module java.desktop
Package javax.swing

Class 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 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.

    See Also:
    JScrollPane, Serialized Form
    • 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

        protected boolean backingStore
        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:
      • 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.

        public static final int BLIT_SCROLL_MODE
        Use graphics.copyArea to implement scrolling. This is the fastest for most applications.
        See Also:
        setScrollMode(int), Constant Field Values

        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.
        See Also:
        setScrollMode(int), Constant Field Values

        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.
        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.
        getUI in class JComponent
        a ViewportUI object
      • 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.)
        addImpl in class Container
        child - the lightweight child of the viewport
        constraints - the constraints to be respected
        index - the index
        See Also:
      • 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.

        scrollRectToVisible in class JComponent
        contentRect - the Rectangle to display
        See Also:
        JComponent.isValidateRoot(), Component.isValid()
      • 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.

        setBorder in class JComponent
        border - the Border to set
        IllegalArgumentException - this method is not implemented
        See Also:
        Border, CompoundBorder
      • 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.
        getInsets in class JComponent
        insets - the Insets object which can be reused
        this viewports inset values
        See Also:
      • 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.
        isOptimizedDrawingEnabled in class JComponent
      • 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.
        isPaintingOrigin in class JComponent
        true if scroll mode is a BACKINGSTORE_SCROLL_MODE.
        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 a StateChanged event.
        reshape in class JComponent
        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

                      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.
        mode - one of the following values:
        • JViewport.BLIT_SCROLL_MODE
        • JViewport.SIMPLE_SCROLL_MODE
        See Also:
      • getScrollMode

        public int getScrollMode()
        Returns the current scrolling mode.
        the scrollMode property
        See Also:
      • isBackingStoreEnabled

        public boolean isBackingStoreEnabled()
        As of Java 2 platform v1.3, replaced by getScrollMode().
        Returns true if this viewport is maintaining an offscreen image of its contents.
        true if scrollMode is BACKINGSTORE_SCROLL_MODE
      • setBackingStoreEnabled

        public void setBackingStoreEnabled​(boolean enabled)
        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.
        enabled - if true, maintain an offscreen backing store
      • setView

        public void setView​(Component view)
        Sets the JViewport's one lightweight child (view), which can be null.
        view - the viewport's new lightweight child
        See Also:
      • 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.
        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.
        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.
        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.
        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.
        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.
        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
        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.
        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.
        size - a Dimension object using pixel coordinates
        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.
        p - a Point object using pixel coordinates
        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.
        newExtent - a Dimension object specifying the size of the view
      • createViewListener

        protected JViewport.ViewListener createViewListener()
        Creates a listener for the view.
        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.
        a LayoutManager
      • getChangeListeners

        public ChangeListener[] getChangeListeners()
        Returns an array of all the ChangeListeners added to this JViewport with addChangeListener().
        all of the ChangeListeners added or an empty array if no listeners have been added
      • 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.
        repaint in class JComponent
        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:
      • 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.
        paramString in class JComponent
        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).
        firePropertyChange in class Component
        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
        getAccessibleContext in class Component
        an AccessibleJViewport that serves as the AccessibleContext of this JViewport