BasicScrollBarUI (Java Platform SE 8 )
Keywords: javax.swing.plaf.basic.BasicScrollBarUI class
Date: 2026-07-22

javax.swing.plaf.basic

## Class BasicScrollBarUI

- java.lang.Object
- - javax.swing.plaf.ComponentUI
  - - javax.swing.plaf.ScrollBarUI
    - - javax.swing.plaf.basic.BasicScrollBarUI

- All Implemented Interfaces:
    LayoutManager, SwingConstants
  Direct Known Subclasses:
    MetalScrollBarUI, SynthScrollBarUI

      public class BasicScrollBarUI
      extends ScrollBarUI
      implements LayoutManager, SwingConstants

  Implementation of ScrollBarUI for the Basic Look and Feel

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `protected class` | `BasicScrollBarUI.ArrowButtonListener` Listener for cursor keys.
    `protected class` | `BasicScrollBarUI.ModelListener` A listener to listen for model changes.
    `class` | `BasicScrollBarUI.PropertyChangeHandler`
    `protected class` | `BasicScrollBarUI.ScrollListener` Listener for scrolling events initiated in the `ScrollPane`.
    `protected class` | `BasicScrollBarUI.TrackListener` Track mouse drags.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected BasicScrollBarUI.ArrowButtonListener` | `buttonListener`
    `protected JButton` | `decrButton`
    `protected static int` | `DECREASE_HIGHLIGHT`
    `protected int` | `decrGap` Distance between the decrement button and the track.
    `protected JButton` | `incrButton`
    `protected static int` | `INCREASE_HIGHLIGHT`
    `protected int` | `incrGap` Distance between the increment button and the track.
    `protected boolean` | `isDragging`
    `protected Dimension` | `maximumThumbSize`
    `protected Dimension` | `minimumThumbSize`
    `protected BasicScrollBarUI.ModelListener` | `modelListener`
    `protected static int` | `NO_HIGHLIGHT`
    `protected PropertyChangeListener` | `propertyChangeListener`
    `protected JScrollBar` | `scrollbar`
    `protected int` | `scrollBarWidth` Hint as to what width (when vertical) or height (when horizontal) should be.
    `protected BasicScrollBarUI.ScrollListener` | `scrollListener`
    `protected Timer` | `scrollTimer`
    `protected Color` | `thumbColor`
    `protected Color` | `thumbDarkShadowColor`
    `protected Color` | `thumbHighlightColor`
    `protected Color` | `thumbLightShadowColor`
    `protected Rectangle` | `thumbRect`
    `protected Color` | `trackColor`
    `protected int` | `trackHighlight`
    `protected Color` | `trackHighlightColor`
    `protected BasicScrollBarUI.TrackListener` | `trackListener`
    `protected Rectangle` | `trackRect`

    - ### Fields inherited from interface javax.swing.SwingConstants

      `BOTTOM, CENTER, EAST, HORIZONTAL, LEADING, LEFT, NEXT, NORTH, NORTH_EAST, NORTH_WEST, PREVIOUS, RIGHT, SOUTH, SOUTH_EAST, SOUTH_WEST, TOP, TRAILING, VERTICAL, WEST`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `BasicScrollBarUI()`

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addLayoutComponent(String name, Component child)` If the layout manager uses a per-component string, adds the component `comp` to the layout, associating it with the string specified by `name`.
    `protected void` | `configureScrollBarColors()`
    `protected BasicScrollBarUI.ArrowButtonListener` | `createArrowButtonListener()`
    `protected JButton` | `createDecreaseButton(int orientation)`
    `protected JButton` | `createIncreaseButton(int orientation)`
    `protected BasicScrollBarUI.ModelListener` | `createModelListener()`
    `protected PropertyChangeListener` | `createPropertyChangeListener()`
    `protected BasicScrollBarUI.ScrollListener` | `createScrollListener()`
    `protected BasicScrollBarUI.TrackListener` | `createTrackListener()`
    `static ComponentUI` | `createUI(JComponent c)`
    `Dimension` | `getMaximumSize(JComponent c)` Returns the specified component's maximum size appropriate for the look and feel.
    `protected Dimension` | `getMaximumThumbSize()` Returns the largest acceptable size for the thumb.
    `protected Dimension` | `getMinimumThumbSize()` Returns the smallest acceptable size for the thumb.
    `Dimension` | `getPreferredSize(JComponent c)` A vertical scrollbar's preferred width is the maximum of preferred widths of the (non `null`) increment/decrement buttons, and the minimum width of the thumb.
    `boolean` | `getSupportsAbsolutePositioning()` Indicates whether the user can absolutely position the thumb with a mouse gesture (usually the middle mouse button).
    `protected Rectangle` | `getThumbBounds()` Return the current size/location of the thumb.
    `protected Rectangle` | `getTrackBounds()` Returns the current bounds of the track, i.e.
    `protected void` | `installComponents()`
    `protected void` | `installDefaults()`
    `protected void` | `installKeyboardActions()`
    `protected void` | `installListeners()`
    `void` | `installUI(JComponent c)` Configures the specified component appropriately for the look and feel.
    `boolean` | `isThumbRollover()` Returns true if the mouse is currently over the thumb.
    `void` | `layoutContainer(Container scrollbarContainer)` Lays out the specified container.
    `protected void` | `layoutHScrollbar(JScrollBar sb)`
    `protected void` | `layoutVScrollbar(JScrollBar sb)`
    `Dimension` | `minimumLayoutSize(Container scrollbarContainer)` Calculates the minimum size dimensions for the specified container, given the components it contains.
    `void` | `paint(Graphics g, JComponent c)` Paints the specified component appropriately for the look and feel.
    `protected void` | `paintDecreaseHighlight(Graphics g)`
    `protected void` | `paintIncreaseHighlight(Graphics g)`
    `protected void` | `paintThumb(Graphics g, JComponent c, Rectangle thumbBounds)`
    `protected void` | `paintTrack(Graphics g, JComponent c, Rectangle trackBounds)`
    `Dimension` | `preferredLayoutSize(Container scrollbarContainer)` Calculates the preferred size dimensions for the specified container, given the components it contains.
    `void` | `removeLayoutComponent(Component child)` Removes the specified component from the layout.
    `protected void` | `scrollByBlock(int direction)`
    `protected void` | `scrollByUnit(int direction)`
    `protected void` | `setThumbBounds(int x, int y, int width, int height)` Set the bounds of the thumb and force a repaint that includes the old thumbBounds and the new one.
    `protected void` | `setThumbRollover(boolean active)` Sets whether or not the mouse is currently over the thumb.
    `protected void` | `uninstallComponents()`
    `protected void` | `uninstallDefaults()`
    `protected void` | `uninstallKeyboardActions()`
    `protected void` | `uninstallListeners()`
    `void` | `uninstallUI(JComponent c)` Reverses configuration which was done on the specified component during `installUI`.

    - ### Methods inherited from class javax.swing.plaf.ComponentUI

      `contains, getAccessibleChild, getAccessibleChildrenCount, getBaseline, getBaselineResizeBehavior, getMinimumSize, update`

    - ### Methods inherited from class java.lang.Object

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

- - ### Field Detail

    - #### minimumThumbSize

          protected Dimension minimumThumbSize

    - #### maximumThumbSize

          protected Dimension maximumThumbSize

    - #### thumbHighlightColor

          protected Color thumbHighlightColor

    - #### thumbLightShadowColor

          protected Color thumbLightShadowColor

    - #### thumbDarkShadowColor

          protected Color thumbDarkShadowColor

    - #### thumbColor

          protected Color thumbColor

    - #### trackColor

          protected Color trackColor

    - #### trackHighlightColor

          protected Color trackHighlightColor

    - #### scrollbar

          protected JScrollBar scrollbar

    - #### incrButton

          protected JButton incrButton

    - #### decrButton

          protected JButton decrButton

    - #### isDragging

          protected boolean isDragging

    - #### trackListener

          protected BasicScrollBarUI.TrackListener trackListener

    - #### buttonListener

          protected BasicScrollBarUI.ArrowButtonListener buttonListener

    - #### modelListener

          protected BasicScrollBarUI.ModelListener modelListener

    - #### thumbRect

          protected Rectangle thumbRect

    - #### trackRect

          protected Rectangle trackRect

    - #### trackHighlight

          protected int trackHighlight

    - #### NO_HIGHLIGHT

          protected static final int NO_HIGHLIGHT

      See Also:
        Constant Field Values

    - #### DECREASE_HIGHLIGHT

          protected static final int DECREASE_HIGHLIGHT

      See Also:
        Constant Field Values

    - #### INCREASE_HIGHLIGHT

          protected static final int INCREASE_HIGHLIGHT

      See Also:
        Constant Field Values

    - #### scrollListener

          protected BasicScrollBarUI.ScrollListener scrollListener

    - #### propertyChangeListener

          protected PropertyChangeListener propertyChangeListener

    - #### scrollTimer

          protected Timer scrollTimer

    - #### scrollBarWidth

          protected int scrollBarWidth

      Hint as to what width (when vertical) or height (when horizontal) should be.
      Since:
        1.7

    - #### incrGap

          protected int incrGap

      Distance between the increment button and the track. This may be a negative number. If negative, then an overlap between the button and track will occur, which is useful for shaped buttons.
      Since:
        1.7

    - #### decrGap

          protected int decrGap

      Distance between the decrement button and the track. This may be a negative number. If negative, then an overlap between the button and track will occur, which is useful for shaped buttons.
      Since:
        1.7

  - ### Constructor Detail

    - #### BasicScrollBarUI

          public BasicScrollBarUI()

  - ### Method Detail

    - #### createUI

          public static ComponentUI createUI(JComponent c)

    - #### configureScrollBarColors

          protected void configureScrollBarColors()

    - #### installUI

          public void installUI(JComponent c)

      Description copied from class: `ComponentUI`
      Configures the specified component appropriately for the look and feel. This method is invoked when the `ComponentUI` instance is being installed as the UI delegate on the specified component. This method should completely configure the component for the look and feel, including the following:
      1. Install default property values for color, fonts, borders, icons, opacity, etc. on the component. Whenever possible, property values initialized by the client program should not be overridden.
      2. Install a `LayoutManager` on the component if necessary.
      3. Create/add any required sub-components to the component.
      4. Create/install event listeners on the component.
      5. Create/install a `PropertyChangeListener` on the component in order to detect and respond to component property changes appropriately.
      6. Install keyboard UI (mnemonics, traversal, etc.) on the component.
      7. Initialize any appropriate instance data.
      Overrides:
        `installUI` in class `ComponentUI`
      Parameters:
        `c` - the component where this UI delegate is being installed
      See Also:
        `ComponentUI.uninstallUI(javax.swing.JComponent)`, `JComponent.setUI(javax.swing.plaf.ComponentUI)`, `JComponent.updateUI()`

    - #### uninstallUI

          public void uninstallUI(JComponent c)

      Description copied from class: `ComponentUI`
      Reverses configuration which was done on the specified component during `installUI`. This method is invoked when this `UIComponent` instance is being removed as the UI delegate for the specified component. This method should undo the configuration performed in `installUI`, being careful to leave the `JComponent` instance in a clean state (no extraneous listeners, look-and-feel-specific property objects, etc.). This should include the following:
      1. Remove any UI-set borders from the component.
      2. Remove any UI-set layout managers on the component.
      3. Remove any UI-added sub-components from the component.
      4. Remove any UI-added event/property listeners from the component.
      5. Remove any UI-installed keyboard UI from the component.
      6. Nullify any allocated instance data objects to allow for GC.
      Overrides:
        `uninstallUI` in class `ComponentUI`
      Parameters:
        `c` - the component from which this UI delegate is being removed; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
      See Also:
        `ComponentUI.installUI(javax.swing.JComponent)`, `JComponent.updateUI()`

    - #### installDefaults

          protected void installDefaults()

    - #### installComponents

          protected void installComponents()

    - #### uninstallComponents

          protected void uninstallComponents()

    - #### installListeners

          protected void installListeners()

    - #### installKeyboardActions

          protected void installKeyboardActions()

    - #### uninstallKeyboardActions

          protected void uninstallKeyboardActions()

    - #### uninstallListeners

          protected void uninstallListeners()

    - #### uninstallDefaults

          protected void uninstallDefaults()

    - #### createTrackListener

          protected BasicScrollBarUI.TrackListener createTrackListener()

    - #### createArrowButtonListener

          protected BasicScrollBarUI.ArrowButtonListener createArrowButtonListener()

    - #### createModelListener

          protected BasicScrollBarUI.ModelListener createModelListener()

    - #### createScrollListener

          protected BasicScrollBarUI.ScrollListener createScrollListener()

    - #### createPropertyChangeListener

          protected PropertyChangeListener createPropertyChangeListener()

    - #### setThumbRollover

          protected void setThumbRollover(boolean active)

      Sets whether or not the mouse is currently over the thumb.
      Parameters:
        `active` - True indicates the thumb is currently active.
      Since:
        1.5

    - #### isThumbRollover

          public boolean isThumbRollover()

      Returns true if the mouse is currently over the thumb.
      Returns:
        true if the thumb is currently active
      Since:
        1.5

    - #### paint

          public void paint(Graphics g,
                            JComponent c)

      Description copied from class: `ComponentUI`
      Paints the specified component appropriately for the look and feel. This method is invoked from the `ComponentUI.update` method when the specified component is being painted. Subclasses should override this method and use the specified `Graphics` object to render the content of the component.
      Overrides:
        `paint` in class `ComponentUI`
      Parameters:
        `g` - the `Graphics` context in which to paint
        `c` - the component being painted; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
      See Also:
        `ComponentUI.update(java.awt.Graphics, javax.swing.JComponent)`

    - #### getPreferredSize

          public Dimension getPreferredSize(JComponent c)

      A vertical scrollbar's preferred width is the maximum of preferred widths of the (non `null`) increment/decrement buttons, and the minimum width of the thumb. The preferred height is the sum of the preferred heights of the same parts. The basis for the preferred size of a horizontal scrollbar is similar.

      The `preferredSize` is only computed once, subsequent calls to this method just return a cached size.

      Overrides:
        `getPreferredSize` in class `ComponentUI`
      Parameters:
        `c` - the `JScrollBar` that's delegating this method to us
      Returns:
        the preferred size of a Basic JScrollBar
      See Also:
        `getMaximumSize(javax.swing.JComponent)`, `ComponentUI.getMinimumSize(javax.swing.JComponent)`

    - #### getMaximumSize

          public Dimension getMaximumSize(JComponent c)

      Description copied from class: `ComponentUI`
      Returns the specified component's maximum size appropriate for the look and feel. If `null` is returned, the maximum size will be calculated by the component's layout manager instead (this is the preferred approach for any component with a specific layout manager installed). The default implementation of this method invokes `getPreferredSize` and returns that value.
      Overrides:
        `getMaximumSize` in class `ComponentUI`
      Parameters:
        `c` - The JScrollBar that's delegating this method to us.
      Returns:
        new Dimension(Integer.MAX_VALUE, Integer.MAX_VALUE);
      See Also:
        `ComponentUI.getMinimumSize(javax.swing.JComponent)`, `getPreferredSize(javax.swing.JComponent)`

    - #### createDecreaseButton

          protected JButton createDecreaseButton(int orientation)

    - #### createIncreaseButton

          protected JButton createIncreaseButton(int orientation)

    - #### paintDecreaseHighlight

          protected void paintDecreaseHighlight(Graphics g)

    - #### paintIncreaseHighlight

          protected void paintIncreaseHighlight(Graphics g)

    - #### paintTrack

          protected void paintTrack(Graphics g,
                                    JComponent c,
                                    Rectangle trackBounds)

    - #### paintThumb

          protected void paintThumb(Graphics g,
                                    JComponent c,
                                    Rectangle thumbBounds)

    - #### getMinimumThumbSize

          protected Dimension getMinimumThumbSize()

      Returns the smallest acceptable size for the thumb. If the scrollbar becomes so small that this size isn't available, the thumb will be hidden.

      Warning : the value returned by this method should not be be modified, it's a shared static constant.

      Returns:
        The smallest acceptable size for the thumb.
      See Also:
        `getMaximumThumbSize()`

    - #### getMaximumThumbSize

          protected Dimension getMaximumThumbSize()

      Returns the largest acceptable size for the thumb. To create a fixed size thumb one make this method and `getMinimumThumbSize` return the same value.

      Warning : the value returned by this method should not be be modified, it's a shared static constant.

      Returns:
        The largest acceptable size for the thumb.
      See Also:
        `getMinimumThumbSize()`

    - #### addLayoutComponent

          public void addLayoutComponent(String name,
                                         Component child)

      Description copied from interface: `LayoutManager`
      If the layout manager uses a per-component string, adds the component `comp` to the layout, associating it with the string specified by `name`.
      Specified by:
        `addLayoutComponent` in interface `LayoutManager`
      Parameters:
        `name` - the string to be associated with the component
        `child` - the component to be added

    - #### removeLayoutComponent

          public void removeLayoutComponent(Component child)

      Description copied from interface: `LayoutManager`
      Removes the specified component from the layout.
      Specified by:
        `removeLayoutComponent` in interface `LayoutManager`
      Parameters:
        `child` - the component to be removed

    - #### preferredLayoutSize

          public Dimension preferredLayoutSize(Container scrollbarContainer)

      Description copied from interface: `LayoutManager`
      Calculates the preferred size dimensions for the specified container, given the components it contains.
      Specified by:
        `preferredLayoutSize` in interface `LayoutManager`
      Parameters:
        `scrollbarContainer` - the container to be laid out
      See Also:
        `LayoutManager.minimumLayoutSize(java.awt.Container)`

    - #### minimumLayoutSize

          public Dimension minimumLayoutSize(Container scrollbarContainer)

      Description copied from interface: `LayoutManager`
      Calculates the minimum size dimensions for the specified container, given the components it contains.
      Specified by:
        `minimumLayoutSize` in interface `LayoutManager`
      Parameters:
        `scrollbarContainer` - the component to be laid out
      See Also:
        `LayoutManager.preferredLayoutSize(java.awt.Container)`

    - #### layoutVScrollbar

          protected void layoutVScrollbar(JScrollBar sb)

    - #### layoutHScrollbar

          protected void layoutHScrollbar(JScrollBar sb)

    - #### layoutContainer

          public void layoutContainer(Container scrollbarContainer)

      Description copied from interface: `LayoutManager`
      Lays out the specified container.
      Specified by:
        `layoutContainer` in interface `LayoutManager`
      Parameters:
        `scrollbarContainer` - the container to be laid out

    - #### setThumbBounds

          protected void setThumbBounds(int x,
                                        int y,
                                        int width,
                                        int height)

      Set the bounds of the thumb and force a repaint that includes the old thumbBounds and the new one.
      See Also:
        `getThumbBounds()`

    - #### getThumbBounds

          protected Rectangle getThumbBounds()

      Return the current size/location of the thumb.

      Warning : the value returned by this method should not be be modified, it's a reference to the actual rectangle, not a copy.

      Returns:
        The current size/location of the thumb.
      See Also:
        `setThumbBounds(int, int, int, int)`

    - #### getTrackBounds

          protected Rectangle getTrackBounds()

      Returns the current bounds of the track, i.e. the space in between the increment and decrement buttons, less the insets. The value returned by this method is updated each time the scrollbar is laid out (validated).

      Warning : the value returned by this method should not be be modified, it's a reference to the actual rectangle, not a copy.

      Returns:
        the current bounds of the scrollbar track
      See Also:
        `layoutContainer(java.awt.Container)`

    - #### scrollByBlock

          protected void scrollByBlock(int direction)

    - #### scrollByUnit

          protected void scrollByUnit(int direction)

    - #### getSupportsAbsolutePositioning

          public boolean getSupportsAbsolutePositioning()

      Indicates whether the user can absolutely position the thumb with a mouse gesture (usually the middle mouse button).
      Returns:
        true if a mouse gesture can absolutely position the thumb
      Since:
        1.5

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