# Class ScrollPaneLayout

java.lang.Object
javax.swing.ScrollPaneLayout

All Implemented Interfaces:
  `LayoutManager`, `Serializable`, `ScrollPaneConstants`

Direct Known Subclasses:
  `ScrollPaneLayout.UIResource`

public class ScrollPaneLayout extends Object implements LayoutManager, ScrollPaneConstants, Serializable
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 JavaBeans has been added to the `java.beans` package. Please see `XMLEncoder`.

Since:
  1.2
See Also:
  - `JScrollPane`
  - `JViewport`

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static class`
  `ScrollPaneLayout.UIResource`
  The UI resource version of `ScrollPaneLayout`.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected JViewport`
  `colHead`
  The column header child.
  `protected JScrollBar`
  `hsb`
  The scrollpane's horizontal scrollbar child.
  `protected int`
  `hsbPolicy`
  The display policy for the horizontal scrollbar.
  `protected Component`
  `lowerLeft`
  The component to display in the lower left corner.
  `protected Component`
  `lowerRight`
  The component to display in the lower right corner.
  `protected JViewport`
  `rowHead`
  The row header child.
  `protected Component`
  `upperLeft`
  The component to display in the upper left corner.
  `protected Component`
  `upperRight`
  The component to display in the upper right corner.
  `protected JViewport`
  `viewport`
  The scrollpane's viewport child.
  `protected JScrollBar`
  `vsb`
  The scrollpane's vertical scrollbar child.
  `protected int`
  `vsbPolicy`
  The display policy for the vertical scrollbar.

  ### Fields declared in interface javax.swing.ScrollPaneConstants

  `COLUMN_HEADER, HORIZONTAL_SCROLLBAR, HORIZONTAL_SCROLLBAR_ALWAYS, HORIZONTAL_SCROLLBAR_AS_NEEDED, HORIZONTAL_SCROLLBAR_NEVER, HORIZONTAL_SCROLLBAR_POLICY, LOWER_LEADING_CORNER, LOWER_LEFT_CORNER, LOWER_RIGHT_CORNER, LOWER_TRAILING_CORNER, ROW_HEADER, UPPER_LEADING_CORNER, UPPER_LEFT_CORNER, UPPER_RIGHT_CORNER, UPPER_TRAILING_CORNER, VERTICAL_SCROLLBAR, VERTICAL_SCROLLBAR_ALWAYS, VERTICAL_SCROLLBAR_AS_NEEDED, VERTICAL_SCROLLBAR_NEVER, VERTICAL_SCROLLBAR_POLICY, VIEWPORT`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `ScrollPaneLayout()`
  Constructs a `ScrollPaneLayout`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addLayoutComponent(String s, Component c)`
  Adds the specified component to the layout.
  `protected Component`
  `addSingletonComponent(Component oldC, Component newC)`
  Removes an existing component.
  `JViewport`
  `getColumnHeader()`
  Returns the `JViewport` object that is the column header.
  `Component`
  `getCorner(String key)`
  Returns the `Component` at the specified corner.
  `JScrollBar`
  `getHorizontalScrollBar()`
  Returns the `JScrollBar` object that handles horizontal scrolling.
  `int`
  `getHorizontalScrollBarPolicy()`
  Returns the horizontal scrollbar-display policy.
  `JViewport`
  `getRowHeader()`
  Returns the `JViewport` object that is the row header.
  `JScrollBar`
  `getVerticalScrollBar()`
  Returns the `JScrollBar` object that handles vertical scrolling.
  `int`
  `getVerticalScrollBarPolicy()`
  Returns the vertical scrollbar-display policy.
  `JViewport`
  `getViewport()`
  Returns the `JViewport` object that displays the scrollable contents.
  `Rectangle`
  `getViewportBorderBounds(JScrollPane scrollpane)`
  Deprecated.
  As of JDK version Swing1.1 replaced by `JScrollPane.getViewportBorderBounds()`.
  `void`
  `layoutContainer(Container parent)`
  Lays out the scrollpane.
  `Dimension`
  `minimumLayoutSize(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.
  `Dimension`
  `preferredLayoutSize(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.
  `void`
  `removeLayoutComponent(Component c)`
  Removes the specified component from the layout.
  `void`
  `setHorizontalScrollBarPolicy(int x)`
  Sets the horizontal scrollbar-display policy.
  `void`
  `setVerticalScrollBarPolicy(int x)`
  Sets the vertical scrollbar-display policy.
  `void`
  `syncWithScrollPane(JScrollPane sp)`
  This method is invoked after the ScrollPaneLayout is set as the LayoutManager of a `JScrollPane`.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### viewport

    protected JViewport viewport
    The scrollpane's viewport child. Default is an empty `JViewport`.
    See Also:
      - `JScrollPane.setViewport(javax.swing.JViewport)`

  - ### vsb

    protected JScrollBar vsb
    The scrollpane's vertical scrollbar child. Default is a `JScrollBar`.
    See Also:
      - `JScrollPane.setVerticalScrollBar(javax.swing.JScrollBar)`

  - ### hsb

    protected JScrollBar hsb
    The scrollpane's horizontal scrollbar child. Default is a `JScrollBar`.
    See Also:
      - `JScrollPane.setHorizontalScrollBar(javax.swing.JScrollBar)`

  - ### rowHead

    protected JViewport rowHead
    The row header child. Default is `null`.
    See Also:
      - `JScrollPane.setRowHeader(javax.swing.JViewport)`

  - ### colHead

    protected JViewport colHead
    The column header child. Default is `null`.
    See Also:
      - `JScrollPane.setColumnHeader(javax.swing.JViewport)`

  - ### lowerLeft

    protected Component lowerLeft
    The component to display in the lower left corner. Default is `null`.
    See Also:
      - `JScrollPane.setCorner(java.lang.String, java.awt.Component)`

  - ### lowerRight

    protected Component lowerRight
    The component to display in the lower right corner. Default is `null`.
    See Also:
      - `JScrollPane.setCorner(java.lang.String, java.awt.Component)`

  - ### upperLeft

    protected Component upperLeft
    The component to display in the upper left corner. Default is `null`.
    See Also:
      - `JScrollPane.setCorner(java.lang.String, java.awt.Component)`

  - ### upperRight

    protected Component upperRight
    The component to display in the upper right corner. Default is `null`.
    See Also:
      - `JScrollPane.setCorner(java.lang.String, java.awt.Component)`

  - ### vsbPolicy

    protected int vsbPolicy
    The display policy for the vertical scrollbar. The default is `ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED`.

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

    See Also:
      - `JScrollPane.setVerticalScrollBarPolicy(int)`

  - ### hsbPolicy

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

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

    See Also:
      - `JScrollPane.setHorizontalScrollBarPolicy(int)`

- ## Constructor Details

  - ### ScrollPaneLayout

    public ScrollPaneLayout()
    Constructs a `ScrollPaneLayout`.

- ## Method Details

  - ### syncWithScrollPane

    public void syncWithScrollPane(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):

    Parameters:
      `sp` - an instance of the `JScrollPane`

  - ### addSingletonComponent

    protected Component addSingletonComponent(Component oldC, 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.

    Parameters:
      `oldC` - the `Component` to replace
      `newC` - the `Component` to add
    Returns:
      the `newC`

  - ### addLayoutComponent

    public void addLayoutComponent(String s, Component c)
    Adds the specified component to the layout. The layout is identified using one of:
    - ScrollPaneConstants.VIEWPORT
    - ScrollPaneConstants.VERTICAL_SCROLLBAR
    - ScrollPaneConstants.HORIZONTAL_SCROLLBAR
    - ScrollPaneConstants.ROW_HEADER
    - ScrollPaneConstants.COLUMN_HEADER
    - ScrollPaneConstants.LOWER_LEFT_CORNER
    - ScrollPaneConstants.LOWER_RIGHT_CORNER
    - ScrollPaneConstants.UPPER_LEFT_CORNER
    - ScrollPaneConstants.UPPER_RIGHT_CORNER
    Specified by:
      `addLayoutComponent` in interface `LayoutManager`
    Parameters:
      `s` - the component identifier
      `c` - the component to be added
    Throws:
      `IllegalArgumentException` - if `s` is an invalid key

  - ### removeLayoutComponent

    public void removeLayoutComponent(Component c)
    Removes the specified component from the layout.
    Specified by:
      `removeLayoutComponent` in interface `LayoutManager`
    Parameters:
      `c` - the component to remove

  - ### getVerticalScrollBarPolicy

    public int getVerticalScrollBarPolicy()
    Returns the vertical scrollbar-display policy.
    Returns:
      an integer giving the display policy
    See Also:
      - `setVerticalScrollBarPolicy(int)`

  - ### setVerticalScrollBarPolicy

    public void setVerticalScrollBarPolicy(int x)
    Sets the vertical scrollbar-display policy. The options are:
    - ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED
    - ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER
    - ScrollPaneConstants.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.
    Parameters:
      `x` - an integer giving the display policy
    Throws:
      `IllegalArgumentException` - if `x` is an invalid vertical scroll bar policy, as listed above

  - ### getHorizontalScrollBarPolicy

    public int getHorizontalScrollBarPolicy()
    Returns the horizontal scrollbar-display policy.
    Returns:
      an integer giving the display policy
    See Also:
      - `setHorizontalScrollBarPolicy(int)`

  - ### setHorizontalScrollBarPolicy

    public void setHorizontalScrollBarPolicy(int x)
    Sets the horizontal scrollbar-display policy. The options are:
    - ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED
    - ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER
    - ScrollPaneConstants.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.
    Parameters:
      `x` - an int giving the display policy
    Throws:
      `IllegalArgumentException` - if `x` is not a valid horizontal scrollbar policy, as listed above

  - ### getViewport

    public JViewport getViewport()
    Returns the `JViewport` object that displays the scrollable contents.
    Returns:
      the `JViewport` object that displays the scrollable contents
    See Also:
      - `JScrollPane.getViewport()`

  - ### getHorizontalScrollBar

    public JScrollBar getHorizontalScrollBar()
    Returns the `JScrollBar` object that handles horizontal scrolling.
    Returns:
      the `JScrollBar` object that handles horizontal scrolling
    See Also:
      - `JScrollPane.getHorizontalScrollBar()`

  - ### getVerticalScrollBar

    public JScrollBar getVerticalScrollBar()
    Returns the `JScrollBar` object that handles vertical scrolling.
    Returns:
      the `JScrollBar` object that handles vertical scrolling
    See Also:
      - `JScrollPane.getVerticalScrollBar()`

  - ### getRowHeader

    public JViewport getRowHeader()
    Returns the `JViewport` object that is the row header.
    Returns:
      the `JViewport` object that is the row header
    See Also:
      - `JScrollPane.getRowHeader()`

  - ### getColumnHeader

    public JViewport getColumnHeader()
    Returns the `JViewport` object that is the column header.
    Returns:
      the `JViewport` object that is the column header
    See Also:
      - `JScrollPane.getColumnHeader()`

  - ### getCorner

    public Component getCorner(String key)
    Returns the `Component` at the specified corner.
    Parameters:
      `key` - the `String` specifying the corner
    Returns:
      the `Component` at the specified corner, as defined in `ScrollPaneConstants`; if `key` is not one of the four corners, `null` is returned
    See Also:
      - `JScrollPane.getCorner(java.lang.String)`

  - ### preferredLayoutSize

    public Dimension preferredLayoutSize(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.

    Specified by:
      `preferredLayoutSize` in interface `LayoutManager`
    Parameters:
      `parent` - the `Container` that will be laid out
    Returns:
      a `Dimension` object specifying the preferred size of the viewport and any scrollbars
    See Also:
      - `ViewportLayout`
      - `LayoutManager`

  - ### minimumLayoutSize

    public Dimension minimumLayoutSize(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.
    Specified by:
      `minimumLayoutSize` in interface `LayoutManager`
    Parameters:
      `parent` - the `Container` that will be laid out
    Returns:
      a `Dimension` object specifying the minimum size
    See Also:
      - `LayoutManager.preferredLayoutSize(java.awt.Container)`

  - ### layoutContainer

    public void layoutContainer(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.
    Specified by:
      `layoutContainer` in interface `LayoutManager`
    Parameters:
      `parent` - the `Container` to lay out

  - ### getViewportBorderBounds

    @Deprecated public Rectangle getViewportBorderBounds(JScrollPane scrollpane)
    Deprecated.
    As of JDK version Swing1.1 replaced by `JScrollPane.getViewportBorderBounds()`.
    Returns the bounds of the border around the specified scroll pane's viewport.
    Parameters:
      `scrollpane` - an instance of the `JScrollPane`
    Returns:
      the size and position of the viewport border