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ScrollPaneLayout.javaAPI DocJava SE 5 API34036Fri Aug 26 14:57:58 BST 2005javax.swing

ScrollPaneLayout

public class ScrollPaneLayout extends Object implements Serializable, LayoutManager, ScrollPaneConstants
The layout manager used by JScrollPane. JScrollPaneLayout is responsible for nine components: a viewport, two scrollbars, a row header, a column header, and four "corner" components.

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 {@link java.beans.XMLEncoder}.

see
JScrollPane
see
JViewport
version
1.60 05/18/04
author
Hans Muller

Fields Summary
protected JViewport
viewport
The scrollpane's viewport child. Default is an empty JViewport.
protected JScrollBar
vsb
The scrollpane's vertical scrollbar child. Default is a JScrollBar.
protected JScrollBar
hsb
The scrollpane's horizontal scrollbar child. Default is a JScrollBar.
protected JViewport
rowHead
The row header child. Default is null.
protected JViewport
colHead
The column header child. Default is null.
protected Component
lowerLeft
The component to display in the lower left corner. Default is null.
protected Component
lowerRight
The component to display in the lower right corner. Default is null.
protected Component
upperLeft
The component to display in the upper left corner. Default is null.
protected Component
upperRight
The component to display in the upper right corner. Default is null.
protected int
vsbPolicy
The display policy for the vertical scrollbar. The default is JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED.

This field is obsolete, please use the JScrollPane field instead.

protected int
hsbPolicy
The display policy for the horizontal scrollbar. The default is JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED.

This field is obsolete, please use the JScrollPane field instead.

Constructors Summary
Methods Summary
public voidaddLayoutComponent(java.lang.String s, java.awt.Component c)
Adds the specified component to the layout. The layout is identified using one of:
  • JScrollPane.VIEWPORT
  • JScrollPane.VERTICAL_SCROLLBAR
  • JScrollPane.HORIZONTAL_SCROLLBAR
  • JScrollPane.ROW_HEADER
  • JScrollPane.COLUMN_HEADER
  • JScrollPane.LOWER_LEFT_CORNER
  • JScrollPane.LOWER_RIGHT_CORNER
  • JScrollPane.UPPER_LEFT_CORNER
  • JScrollPane.UPPER_RIGHT_CORNER

param
s the component identifier
param
c the the component to be added
exception
IllegalArgumentException if s is an invalid key

	if (s.equals(VIEWPORT)) {
	    viewport = (JViewport)addSingletonComponent(viewport, c);
	}
	else if (s.equals(VERTICAL_SCROLLBAR)) {
	    vsb = (JScrollBar)addSingletonComponent(vsb, c);
	}
	else if (s.equals(HORIZONTAL_SCROLLBAR)) {
	    hsb = (JScrollBar)addSingletonComponent(hsb, c);
	}
	else if (s.equals(ROW_HEADER)) {
	    rowHead = (JViewport)addSingletonComponent(rowHead, c);
	}
	else if (s.equals(COLUMN_HEADER)) {
	    colHead = (JViewport)addSingletonComponent(colHead, c);
	}
	else if (s.equals(LOWER_LEFT_CORNER)) {
	    lowerLeft = addSingletonComponent(lowerLeft, c);
	}
	else if (s.equals(LOWER_RIGHT_CORNER)) {
	    lowerRight = addSingletonComponent(lowerRight, c);
	}
	else if (s.equals(UPPER_LEFT_CORNER)) {
	    upperLeft = addSingletonComponent(upperLeft, c);
	}
	else if (s.equals(UPPER_RIGHT_CORNER)) {
	    upperRight = addSingletonComponent(upperRight, c);
	}
	else {
	    throw new IllegalArgumentException("invalid layout key " + s);
	}
protected java.awt.ComponentaddSingletonComponent(java.awt.Component oldC, java.awt.Component newC)
Removes an existing component. When a new component, such as the left corner, or vertical scrollbar, is added, the old one, if it exists, must be removed.

This method returns newC. If oldC is not equal to newC and is non-null, it will be removed from its parent.

param
oldC the Component to replace
param
newC the Component to add
return
the newC

	if ((oldC != null) && (oldC != newC)) {
	    oldC.getParent().remove(oldC);
	}
	return newC;
private voidadjustForHSB(boolean wantsHSB, java.awt.Rectangle available, java.awt.Rectangle hsbR, java.awt.Insets vpbInsets)
Adjusts the Rectangle available based on if the horizontal scrollbar is needed (wantsHSB). The location of the hsb is updated in hsbR, and the viewport border insets (vpbInsets) are used to offset the hsb. This is only called when wantsHSB has changed, eg you shouldn't invoked adjustForHSB(true) twice.

        int oldHeight = hsbR.height;
	if (wantsHSB) {
            int hsbHeight = Math.max(0, Math.min(available.height,
                                              hsb.getPreferredSize().height));

	    available.height -= hsbHeight;
	    hsbR.y = available.y + available.height + vpbInsets.bottom;
	    hsbR.height = hsbHeight;
	}
	else {
	    available.height += oldHeight;
	}
private voidadjustForVSB(boolean wantsVSB, java.awt.Rectangle available, java.awt.Rectangle vsbR, java.awt.Insets vpbInsets, boolean leftToRight)
Adjusts the Rectangle available based on if the vertical scrollbar is needed (wantsVSB). The location of the vsb is updated in vsbR, and the viewport border insets (vpbInsets) are used to offset the vsb. This is only called when wantsVSB has changed, eg you shouldn't invoke adjustForVSB(true) twice.

        int oldWidth = vsbR.width;
	if (wantsVSB) {
            int vsbWidth = Math.max(0, Math.min(vsb.getPreferredSize().width,
                                                available.width));

	    available.width -= vsbWidth;
	    vsbR.width = vsbWidth;
            
            if( leftToRight ) {
                vsbR.x = available.x + available.width + vpbInsets.right;
            } else {
                vsbR.x = available.x - vpbInsets.left;
                available.x += vsbWidth;
            }
	}
	else {
	    available.width += oldWidth;
	}
public javax.swing.JViewportgetColumnHeader()
Returns the JViewport object that is the column header.

return
the JViewport object that is the column header
see
JScrollPane#getColumnHeader

	return colHead;
public java.awt.ComponentgetCorner(java.lang.String key)
Returns the Component at the specified corner.

param
key the String specifying the corner
return
the Component at the specified corner, as defined in {@link ScrollPaneConstants}; if key is not one of the four corners, null is returned
see
JScrollPane#getCorner

	if (key.equals(LOWER_LEFT_CORNER)) {
	    return lowerLeft;
	}
	else if (key.equals(LOWER_RIGHT_CORNER)) {
	    return lowerRight;
	}
	else if (key.equals(UPPER_LEFT_CORNER)) {
	    return upperLeft;
	}
	else if (key.equals(UPPER_RIGHT_CORNER)) {
	    return upperRight;
	}
	else {
	    return null;
	}
public javax.swing.JScrollBargetHorizontalScrollBar()
Returns the JScrollBar object that handles horizontal scrolling.

return
the JScrollBar object that handles horizontal scrolling
see
JScrollPane#getHorizontalScrollBar

	return hsb;
public intgetHorizontalScrollBarPolicy()
Returns the horizontal scrollbar-display policy.

return
an integer giving the display policy
see
#setHorizontalScrollBarPolicy

	return hsbPolicy;
public javax.swing.JViewportgetRowHeader()
Returns the JViewport object that is the row header.

return
the JViewport object that is the row header
see
JScrollPane#getRowHeader

	return rowHead;
public javax.swing.JScrollBargetVerticalScrollBar()
Returns the JScrollBar object that handles vertical scrolling.

return
the JScrollBar object that handles vertical scrolling
see
JScrollPane#getVerticalScrollBar

	return vsb;
public intgetVerticalScrollBarPolicy()
Returns the vertical scrollbar-display policy.

return
an integer giving the display policy
see
#setVerticalScrollBarPolicy

	return vsbPolicy;
public javax.swing.JViewportgetViewport()
Returns the JViewport object that displays the scrollable contents.

return
the JViewport object that displays the scrollable contents
see
JScrollPane#getViewport

	return viewport;
public java.awt.RectanglegetViewportBorderBounds(javax.swing.JScrollPane scrollpane)
Returns the bounds of the border around the specified scroll pane's viewport.

return
the size and position of the viewport border
deprecated
As of JDK version Swing1.1 replaced by JScrollPane.getViewportBorderBounds().

	return scrollpane.getViewportBorderBounds();
public voidlayoutContainer(java.awt.Container parent)
Lays out the scrollpane. The positioning of components depends on the following constraints:
  • The row header, if present and visible, gets its preferred width and the viewport's height.
  • The column header, if present and visible, gets its preferred height and the viewport's width.
  • If a vertical scrollbar is needed, i.e. if the viewport's extent height is smaller than its view height or if the displayPolicy is ALWAYS, it's treated like the row header with respect to its dimensions and is made visible.
  • If a horizontal scrollbar is needed, it is treated like the column header (see the paragraph above regarding the vertical scrollbar).
  • If the scrollpane has a non-null viewportBorder, then space is allocated for that.
  • The viewport gets the space available after accounting for the previous constraints.
  • The corner components, if provided, are aligned with the ends of the scrollbars and headers. If there is a vertical scrollbar, the right corners appear; if there is a horizontal scrollbar, the lower corners appear; a row header gets left corners, and a column header gets upper corners.

param
parent the Container to lay out

	/* Sync the (now obsolete) policy fields with the
	 * JScrollPane.
	 */
	JScrollPane scrollPane = (JScrollPane)parent;
	vsbPolicy = scrollPane.getVerticalScrollBarPolicy();
	hsbPolicy = scrollPane.getHorizontalScrollBarPolicy();

	Rectangle availR = scrollPane.getBounds();
	availR.x = availR.y = 0;

	Insets insets = parent.getInsets();
	availR.x = insets.left;
	availR.y = insets.top;
	availR.width -= insets.left + insets.right;
	availR.height -= insets.top + insets.bottom;

        /* Get the scrollPane's orientation.
         */
        boolean leftToRight = SwingUtilities.isLeftToRight(scrollPane);

	/* If there's a visible column header remove the space it 
	 * needs from the top of availR.  The column header is treated 
	 * as if it were fixed height, arbitrary width.
	 */

	Rectangle colHeadR = new Rectangle(0, availR.y, 0, 0);

	if ((colHead != null) && (colHead.isVisible())) {
	    int colHeadHeight = Math.min(availR.height,
                                         colHead.getPreferredSize().height);
	    colHeadR.height = colHeadHeight; 
	    availR.y += colHeadHeight;
	    availR.height -= colHeadHeight;
	}

	/* If there's a visible row header remove the space it needs
	 * from the left or right of availR.  The row header is treated 
	 * as if it were fixed width, arbitrary height.
	 */

	Rectangle rowHeadR = new Rectangle(0, 0, 0, 0);
	
	if ((rowHead != null) && (rowHead.isVisible())) {
	    int rowHeadWidth = Math.min(availR.width,
                                        rowHead.getPreferredSize().width);
	    rowHeadR.width = rowHeadWidth;
	    availR.width -= rowHeadWidth;
            if ( leftToRight ) {
                rowHeadR.x = availR.x;
                availR.x += rowHeadWidth;
            } else {
                rowHeadR.x = availR.x + availR.width;
            }
	}

	/* If there's a JScrollPane.viewportBorder, remove the
	 * space it occupies for availR.
	 */

	Border viewportBorder = scrollPane.getViewportBorder();
	Insets vpbInsets;
	if (viewportBorder != null) {
	    vpbInsets = viewportBorder.getBorderInsets(parent);
	    availR.x += vpbInsets.left;
	    availR.y += vpbInsets.top;
	    availR.width -= vpbInsets.left + vpbInsets.right;
	    availR.height -= vpbInsets.top + vpbInsets.bottom;
	}
	else {
	    vpbInsets = new Insets(0,0,0,0);
	}


	/* At this point availR is the space available for the viewport
	 * and scrollbars. rowHeadR is correct except for its height and y
         * and colHeadR is correct except for its width and x.  Once we're 
	 * through computing the dimensions  of these three parts we can 
	 * go back and set the dimensions of rowHeadR.height, rowHeadR.y,
         * colHeadR.width, colHeadR.x and the bounds for the corners.
	 * 
         * We'll decide about putting up scrollbars by comparing the 
         * viewport views preferred size with the viewports extent
	 * size (generally just its size).  Using the preferredSize is
	 * reasonable because layout proceeds top down - so we expect
	 * the viewport to be laid out next.  And we assume that the
	 * viewports layout manager will give the view it's preferred
	 * size.  One exception to this is when the view implements 
	 * Scrollable and Scrollable.getViewTracksViewport{Width,Height}
	 * methods return true.  If the view is tracking the viewports
	 * width we don't bother with a horizontal scrollbar, similarly
	 * if view.getViewTracksViewport(Height) is true we don't bother
	 * with a vertical scrollbar.
	 */

	Component view = (viewport != null) ? viewport.getView() : null;
	Dimension viewPrefSize =  
	    (view != null) ? view.getPreferredSize() 
                           : new Dimension(0,0);

	Dimension extentSize = 
	    (viewport != null) ? viewport.toViewCoordinates(availR.getSize()) 
	                       : new Dimension(0,0);

	boolean viewTracksViewportWidth = false;
	boolean viewTracksViewportHeight = false;
        boolean isEmpty = (availR.width < 0 || availR.height < 0);
	Scrollable sv;
        // Don't bother checking the Scrollable methods if there is no room
        // for the viewport, we aren't going to show any scrollbars in this
        // case anyway.
	if (!isEmpty && view instanceof Scrollable) {
	    sv = (Scrollable)view;
	    viewTracksViewportWidth = sv.getScrollableTracksViewportWidth();
	    viewTracksViewportHeight = sv.getScrollableTracksViewportHeight();
	}
	else {
	    sv = null;
	}

	/* If there's a vertical scrollbar and we need one, allocate
	 * space for it (we'll make it visible later). A vertical 
	 * scrollbar is considered to be fixed width, arbitrary height.
	 */

	Rectangle vsbR = new Rectangle(0, availR.y - vpbInsets.top, 0, 0);

	boolean vsbNeeded;
        if (isEmpty) {
            vsbNeeded = false;
        }
	else if (vsbPolicy == VERTICAL_SCROLLBAR_ALWAYS) {
	    vsbNeeded = true;
	}
	else if (vsbPolicy == VERTICAL_SCROLLBAR_NEVER) {
	    vsbNeeded = false;
	}
	else {  // vsbPolicy == VERTICAL_SCROLLBAR_AS_NEEDED
	    vsbNeeded = !viewTracksViewportHeight && (viewPrefSize.height > extentSize.height);
	}


	if ((vsb != null) && vsbNeeded) {
	    adjustForVSB(true, availR, vsbR, vpbInsets, leftToRight);
	    extentSize = viewport.toViewCoordinates(availR.getSize());
	}
	
	/* If there's a horizontal scrollbar and we need one, allocate
	 * space for it (we'll make it visible later). A horizontal 
	 * scrollbar is considered to be fixed height, arbitrary width.
	 */

	Rectangle hsbR = new Rectangle(availR.x - vpbInsets.left, 0, 0, 0);
	boolean hsbNeeded;
        if (isEmpty) {
            hsbNeeded = false;
        }
	else if (hsbPolicy == HORIZONTAL_SCROLLBAR_ALWAYS) {
	    hsbNeeded = true;
	}
	else if (hsbPolicy == HORIZONTAL_SCROLLBAR_NEVER) {
	    hsbNeeded = false;
	}
	else {  // hsbPolicy == HORIZONTAL_SCROLLBAR_AS_NEEDED
	    hsbNeeded = !viewTracksViewportWidth && (viewPrefSize.width > extentSize.width);
	}

	if ((hsb != null) && hsbNeeded) {
	    adjustForHSB(true, availR, hsbR, vpbInsets);

	    /* If we added the horizontal scrollbar then we've implicitly 
	     * reduced  the vertical space available to the viewport. 
	     * As a consequence we may have to add the vertical scrollbar, 
	     * if that hasn't been done so already.  Of course we
	     * don't bother with any of this if the vsbPolicy is NEVER.
	     */
	    if ((vsb != null) && !vsbNeeded &&
		(vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {

		extentSize = viewport.toViewCoordinates(availR.getSize());
		vsbNeeded = viewPrefSize.height > extentSize.height;

		if (vsbNeeded) {
		    adjustForVSB(true, availR, vsbR, vpbInsets, leftToRight);
		}
	    }
	}

	/* Set the size of the viewport first, and then recheck the Scrollable
	 * methods. Some components base their return values for the Scrollable
	 * methods on the size of the Viewport, so that if we don't
	 * ask after resetting the bounds we may have gotten the wrong
	 * answer.
	 */
	
	if (viewport != null) {
	    viewport.setBounds(availR);

	    if (sv != null) {
		extentSize = viewport.toViewCoordinates(availR.getSize());

		boolean oldHSBNeeded = hsbNeeded;
		boolean oldVSBNeeded = vsbNeeded;
		viewTracksViewportWidth = sv.
		                          getScrollableTracksViewportWidth();
		viewTracksViewportHeight = sv.
		                          getScrollableTracksViewportHeight();
		if (vsb != null && vsbPolicy == VERTICAL_SCROLLBAR_AS_NEEDED) {
		    boolean newVSBNeeded = !viewTracksViewportHeight &&
		                     (viewPrefSize.height > extentSize.height);
		    if (newVSBNeeded != vsbNeeded) {
			vsbNeeded = newVSBNeeded;
			adjustForVSB(vsbNeeded, availR, vsbR, vpbInsets,
				     leftToRight);
			extentSize = viewport.toViewCoordinates
			                      (availR.getSize());
		    }
		}
		if (hsb != null && hsbPolicy ==HORIZONTAL_SCROLLBAR_AS_NEEDED){
		    boolean newHSBbNeeded = !viewTracksViewportWidth &&
			               (viewPrefSize.width > extentSize.width);
		    if (newHSBbNeeded != hsbNeeded) {
			hsbNeeded = newHSBbNeeded;
			adjustForHSB(hsbNeeded, availR, hsbR, vpbInsets);
			if ((vsb != null) && !vsbNeeded &&
			    (vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {

			    extentSize = viewport.toViewCoordinates
				         (availR.getSize());
			    vsbNeeded = viewPrefSize.height >
				        extentSize.height;

			    if (vsbNeeded) {
				adjustForVSB(true, availR, vsbR, vpbInsets,
					     leftToRight);
			    }
			}
		    }
		}
		if (oldHSBNeeded != hsbNeeded ||
		    oldVSBNeeded != vsbNeeded) {
		    viewport.setBounds(availR);
		    // You could argue that we should recheck the
		    // Scrollable methods again until they stop changing,
		    // but they might never stop changing, so we stop here
		    // and don't do any additional checks.
		}
	    }
	}

	/* We now have the final size of the viewport: availR.
	 * Now fixup the header and scrollbar widths/heights.
	 */
	vsbR.height = availR.height + vpbInsets.top + vpbInsets.bottom;
	hsbR.width = availR.width + vpbInsets.left + vpbInsets.right;
	rowHeadR.height = availR.height + vpbInsets.top + vpbInsets.bottom;
        rowHeadR.y = availR.y - vpbInsets.top;
	colHeadR.width = availR.width + vpbInsets.left + vpbInsets.right;
        colHeadR.x = availR.x - vpbInsets.left;

	/* Set the bounds of the remaining components.  The scrollbars
	 * are made invisible if they're not needed.
	 */
	
	if (rowHead != null) {
	    rowHead.setBounds(rowHeadR);
	}

	if (colHead != null) {
	    colHead.setBounds(colHeadR);
	}

	if (vsb != null) {
	    if (vsbNeeded) {
		vsb.setVisible(true);
		vsb.setBounds(vsbR);
	    }
	    else {
		vsb.setVisible(false);
	    }
	}

	if (hsb != null) {
	    if (hsbNeeded) {
		hsb.setVisible(true);
		hsb.setBounds(hsbR);
	    }
	    else {
		hsb.setVisible(false);
	    }
	}

	if (lowerLeft != null) {
	    lowerLeft.setBounds(leftToRight ? rowHeadR.x : vsbR.x,
                                hsbR.y,
                                leftToRight ? rowHeadR.width : vsbR.width,
                                hsbR.height);
	}

	if (lowerRight != null) {
	    lowerRight.setBounds(leftToRight ? vsbR.x : rowHeadR.x,
                                 hsbR.y,
                                 leftToRight ? vsbR.width : rowHeadR.width,
                                 hsbR.height);
	}

	if (upperLeft != null) {
	    upperLeft.setBounds(leftToRight ? rowHeadR.x : vsbR.x,
                                colHeadR.y,
                                leftToRight ? rowHeadR.width : vsbR.width,
                                colHeadR.height);
	}

	if (upperRight != null) {
	    upperRight.setBounds(leftToRight ? vsbR.x : rowHeadR.x,
                                 colHeadR.y,
                                 leftToRight ? vsbR.width : rowHeadR.width,
                                 colHeadR.height);
	}
public java.awt.DimensionminimumLayoutSize(java.awt.Container parent)
The minimum size of a ScrollPane is the size of the insets plus minimum size of the viewport, plus the scrollpane's viewportBorder insets, plus the minimum size of the visible headers, plus the minimum size of the scrollbars whose displayPolicy isn't NEVER.

param
parent the Container that will be laid out
return
a Dimension object specifying the minimum size

	/* Sync the (now obsolete) policy fields with the
	 * JScrollPane.
	 */
	JScrollPane scrollPane = (JScrollPane)parent;
	vsbPolicy = scrollPane.getVerticalScrollBarPolicy();
	hsbPolicy = scrollPane.getHorizontalScrollBarPolicy();

	Insets insets = parent.getInsets();
	int minWidth = insets.left + insets.right;
	int minHeight = insets.top + insets.bottom;
	
	/* If there's a viewport add its minimumSize.
	 */
	
	if (viewport != null) {
	    Dimension size = viewport.getMinimumSize();
	    minWidth += size.width;
	    minHeight += size.height;
	}

	/* If there's a JScrollPane.viewportBorder, add its insets.
	 */

	Border viewportBorder = scrollPane.getViewportBorder();
	if (viewportBorder != null) {
	    Insets vpbInsets = viewportBorder.getBorderInsets(parent);
	    minWidth += vpbInsets.left + vpbInsets.right;
	    minHeight += vpbInsets.top + vpbInsets.bottom;
	}

	/* If a header exists and it's visible, factor its
	 * minimum size in.
	 */

	if ((rowHead != null) && rowHead.isVisible()) {
	    Dimension size = rowHead.getMinimumSize();
	    minWidth += size.width;
	    minHeight = Math.max(minHeight, size.height);
	}

	if ((colHead != null) && colHead.isVisible()) {
	    Dimension size = colHead.getMinimumSize();
	    minWidth = Math.max(minWidth, size.width);
	    minHeight += size.height;
	}

	/* If a scrollbar might appear, factor its minimum
	 * size in.
	 */

	if ((vsb != null) && (vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {
	    Dimension size = vsb.getMinimumSize();
	    minWidth += size.width;
	    minHeight = Math.max(minHeight, size.height);
	}

	if ((hsb != null) && (hsbPolicy != HORIZONTAL_SCROLLBAR_NEVER)) {
	    Dimension size = hsb.getMinimumSize();
	    minWidth = Math.max(minWidth, size.width);
	    minHeight += size.height;
	}

	return new Dimension(minWidth, minHeight);
public java.awt.DimensionpreferredLayoutSize(java.awt.Container parent)
The preferred size of a ScrollPane is the size of the insets, plus the preferred size of the viewport, plus the preferred size of the visible headers, plus the preferred size of the scrollbars that will appear given the current view and the current scrollbar displayPolicies.

Note that the rowHeader is calculated as part of the preferred width and the colHeader is calculated as part of the preferred size.

param
parent the Container that will be laid out
return
a Dimension object specifying the preferred size of the viewport and any scrollbars
see
ViewportLayout
see
LayoutManager

	/* Sync the (now obsolete) policy fields with the
	 * JScrollPane.
	 */
	JScrollPane scrollPane = (JScrollPane)parent;
	vsbPolicy = scrollPane.getVerticalScrollBarPolicy();
	hsbPolicy = scrollPane.getHorizontalScrollBarPolicy();

	Insets insets = parent.getInsets();
	int prefWidth = insets.left + insets.right;
	int prefHeight = insets.top + insets.bottom;

	/* Note that viewport.getViewSize() is equivalent to 
	 * viewport.getView().getPreferredSize() modulo a null
	 * view or a view whose size was explicitly set.
	 */

	Dimension extentSize = null;
	Dimension viewSize = null;
	Component view = null;

	if (viewport !=  null) {
	    extentSize = viewport.getPreferredSize();
	    viewSize = viewport.getViewSize();
	    view = viewport.getView();
	}

	/* If there's a viewport add its preferredSize.
	 */

	if (extentSize != null) {
	    prefWidth += extentSize.width;
	    prefHeight += extentSize.height;
	}

	/* If there's a JScrollPane.viewportBorder, add its insets.
	 */

	Border viewportBorder = scrollPane.getViewportBorder();
	if (viewportBorder != null) {
	    Insets vpbInsets = viewportBorder.getBorderInsets(parent);
	    prefWidth += vpbInsets.left + vpbInsets.right;
	    prefHeight += vpbInsets.top + vpbInsets.bottom;
	}

	/* If a header exists and it's visible, factor its
	 * preferred size in.
	 */

	if ((rowHead != null) && rowHead.isVisible()) {
	    prefWidth += rowHead.getPreferredSize().width;
	}

	if ((colHead != null) && colHead.isVisible()) {
	    prefHeight += colHead.getPreferredSize().height;
	}

	/* If a scrollbar is going to appear, factor its preferred size in.
	 * If the scrollbars policy is AS_NEEDED, this can be a little
	 * tricky:
	 * 
	 * - If the view is a Scrollable then scrollableTracksViewportWidth
	 * and scrollableTracksViewportHeight can be used to effectively 
	 * disable scrolling (if they're true) in their respective dimensions.
	 * 
	 * - Assuming that a scrollbar hasn't been disabled by the 
	 * previous constraint, we need to decide if the scrollbar is going 
	 * to appear to correctly compute the JScrollPanes preferred size.
	 * To do this we compare the preferredSize of the viewport (the 
	 * extentSize) to the preferredSize of the view.  Although we're
	 * not responsible for laying out the view we'll assume that the 
	 * JViewport will always give it its preferredSize.
	 */

	if ((vsb != null) && (vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {
	    if (vsbPolicy == VERTICAL_SCROLLBAR_ALWAYS) {
		prefWidth += vsb.getPreferredSize().width;
	    }
	    else if ((viewSize != null) && (extentSize != null)) {
		boolean canScroll = true;
		if (view instanceof Scrollable) {
		    canScroll = !((Scrollable)view).getScrollableTracksViewportHeight();
		}
		if (canScroll && (viewSize.height > extentSize.height)) {
		    prefWidth += vsb.getPreferredSize().width;
		}
	    }
	}

	if ((hsb != null) && (hsbPolicy != HORIZONTAL_SCROLLBAR_NEVER)) {
	    if (hsbPolicy == HORIZONTAL_SCROLLBAR_ALWAYS) {
		prefHeight += hsb.getPreferredSize().height;
	    }
	    else if ((viewSize != null) && (extentSize != null)) {
		boolean canScroll = true;
		if (view instanceof Scrollable) {
		    canScroll = !((Scrollable)view).getScrollableTracksViewportWidth();
		}
		if (canScroll && (viewSize.width > extentSize.width)) {
		    prefHeight += hsb.getPreferredSize().height;
		}
	    }
	}

	return new Dimension(prefWidth, prefHeight);
public voidremoveLayoutComponent(java.awt.Component c)
Removes the specified component from the layout.

param
c the component to remove

	if (c == viewport) {
	    viewport = null;
	}
	else if (c == vsb) {
	    vsb = null;
	}
	else if (c == hsb) {
	    hsb = null;
	}
	else if (c == rowHead) {
	    rowHead = null;
	}
	else if (c == colHead) {
	    colHead = null;
	}
	else if (c == lowerLeft) {
	    lowerLeft = null;
	}
	else if (c == lowerRight) {
	    lowerRight = null;
	}
	else if (c == upperLeft) {
	    upperLeft = null;
	}
	else if (c == upperRight) {
	    upperRight = null;
	}
public voidsetHorizontalScrollBarPolicy(int x)
Sets the horizontal scrollbar-display policy. The options are:
  • JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED
  • JScrollPane.HOTRIZONTAL_SCROLLBAR_NEVER
  • JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS
Note: Applications should use the JScrollPane version of this method. It only exists for backwards compatibility with the Swing 1.0.2 (and earlier) versions of this class.

param
x an int giving the display policy
exception
IllegalArgumentException if x is not a valid horizontal scrollbar policy, as listed above

	switch (x) {
	case HORIZONTAL_SCROLLBAR_AS_NEEDED:
	case HORIZONTAL_SCROLLBAR_NEVER:
	case HORIZONTAL_SCROLLBAR_ALWAYS:
	    	hsbPolicy = x;
		break;
	default:
	    throw new IllegalArgumentException("invalid horizontalScrollBarPolicy");
	}
public voidsetVerticalScrollBarPolicy(int x)
Sets the vertical scrollbar-display policy. The options are:
  • JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED
  • JScrollPane.VERTICAL_SCROLLBAR_NEVER
  • JScrollPane.VERTICAL_SCROLLBAR_ALWAYS
Note: Applications should use the JScrollPane version of this method. It only exists for backwards compatibility with the Swing 1.0.2 (and earlier) versions of this class.

param
x an integer giving the display policy
exception
IllegalArgumentException if x is an invalid vertical scroll bar policy, as listed above

	switch (x) {
	case VERTICAL_SCROLLBAR_AS_NEEDED:
	case VERTICAL_SCROLLBAR_NEVER:
	case VERTICAL_SCROLLBAR_ALWAYS:
	    	vsbPolicy = x;
		break;
	default:
	    throw new IllegalArgumentException("invalid verticalScrollBarPolicy");
	}
public voidsyncWithScrollPane(javax.swing.JScrollPane sp)
This method is invoked after the ScrollPaneLayout is set as the LayoutManager of a JScrollPane. It initializes all of the internal fields that are ordinarily set by addLayoutComponent. For example: 
ScrollPaneLayout mySPLayout = new ScrollPanelLayout() {
public void layoutContainer(Container p) {
super.layoutContainer(p);
// do some extra work here ...
}
};
scrollpane.setLayout(mySPLayout):




                                                                                        
        
	viewport = sp.getViewport();
	vsb = sp.getVerticalScrollBar();
	hsb = sp.getHorizontalScrollBar();
	rowHead = sp.getRowHeader();
	colHead = sp.getColumnHeader();
	lowerLeft = sp.getCorner(LOWER_LEFT_CORNER);
	lowerRight = sp.getCorner(LOWER_RIGHT_CORNER);
	upperLeft = sp.getCorner(UPPER_LEFT_CORNER);
	upperRight = sp.getCorner(UPPER_RIGHT_CORNER);
	vsbPolicy = sp.getVerticalScrollBarPolicy();
	hsbPolicy = sp.getHorizontalScrollBarPolicy();