Class BasicScrollBarUI

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

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

Field Summary

Modifier and Type	Field	Description
`protected BasicScrollBarUI.ArrowButtonListener`	`buttonListener`	Button listener
`protected JButton`	`decrButton`	Decrement button
`protected static final int`	`DECREASE_HIGHLIGHT`	Decrease highlight
`protected int`	`decrGap`	Distance between the decrement button and the track.
`protected JButton`	`incrButton`	Increment button
`protected static final int`	`INCREASE_HIGHLIGHT`	Increase highlight
`protected int`	`incrGap`	Distance between the increment button and the track.
`protected boolean`	`isDragging`	Dragging
`protected Dimension`	`maximumThumbSize`	Maximum thumb size
`protected Dimension`	`minimumThumbSize`	Minimum thumb size
`protected BasicScrollBarUI.ModelListener`	`modelListener`	Model listener
`protected static final int`	`NO_HIGHLIGHT`	No highlight
`protected PropertyChangeListener`	`propertyChangeListener`	Property change listener
`protected JScrollBar`	`scrollbar`	Scrollbar
`protected int`	`scrollBarWidth`	Hint as to what width (when vertical) or height (when horizontal) should be.
`protected BasicScrollBarUI.ScrollListener`	`scrollListener`	Scroll listener
`protected Timer`	`scrollTimer`	Scroll timer
`protected Color`	`thumbColor`	Thumb color
`protected Color`	`thumbDarkShadowColor`	Thumb dark shadow color
`protected Color`	`thumbHighlightColor`	Thumb highlight color
`protected Color`	`thumbLightShadowColor`	Thumb light shadow color
`protected Rectangle`	`thumbRect`	Thumb rectangle
`protected Color`	`trackColor`	Track color
`protected int`	`trackHighlight`	Track highlight
`protected Color`	`trackHighlightColor`	Track highlight color
`protected BasicScrollBarUI.TrackListener`	`trackListener`	Track listener
`protected Rectangle`	`trackRect`	Track rectangle

Fields declared in interface SwingConstants

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

Modifier and Type	Field	Description
`static final int`	`BOTTOM`	Box-orientation constant used to specify the bottom of a box.
`static final int`	`CENTER`	The central position in an area.
`static final int`	`EAST`	Compass-direction east (right).
`static final int`	`HORIZONTAL`	Horizontal orientation.
`static final int`	`LEADING`	Identifies the leading edge of text for use with left-to-right and right-to-left languages.
`static final int`	`LEFT`	Box-orientation constant used to specify the left side of a box.
`static final int`	`NEXT`	Identifies the next direction in a sequence.
`static final int`	`NORTH`	Compass-direction North (up).
`static final int`	`NORTH_EAST`	Compass-direction north-east (upper right).
`static final int`	`NORTH_WEST`	Compass-direction north west (upper left).
`static final int`	`PREVIOUS`	Identifies the previous direction in a sequence.
`static final int`	`RIGHT`	Box-orientation constant used to specify the right side of a box.
`static final int`	`SOUTH`	Compass-direction south (down).
`static final int`	`SOUTH_EAST`	Compass-direction south-east (lower right).
`static final int`	`SOUTH_WEST`	Compass-direction south-west (lower left).
`static final int`	`TOP`	Box-orientation constant used to specify the top of a box.
`static final int`	`TRAILING`	Identifies the trailing edge of text for use with left-to-right and right-to-left languages.
`static final int`	`VERTICAL`	Vertical orientation.
`static final int`	`WEST`	Compass-direction west (left).

Constructor Summary

Constructor	Description
`BasicScrollBarUI()`	Constructs a `BasicScrollBarUI`.

Method Summary

Modifier and Type	Method	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()`	Configures the scroll bar colors.
`protected BasicScrollBarUI.ArrowButtonListener`	`createArrowButtonListener()`	Creates an arrow button listener.
`protected JButton`	`createDecreaseButton(int orientation)`	Creates a decrease button.
`protected JButton`	`createIncreaseButton(int orientation)`	Creates an increase button.
`protected BasicScrollBarUI.ModelListener`	`createModelListener()`	Creates a model listener.
`protected PropertyChangeListener`	`createPropertyChangeListener()`	Creates a property change listener.
`protected BasicScrollBarUI.ScrollListener`	`createScrollListener()`	Creates a scroll listener.
`protected BasicScrollBarUI.TrackListener`	`createTrackListener()`	Creates a track listener.
`static ComponentUI`	`createUI(JComponent c)`	Creates the UI.
`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. the space in between the increment and decrement buttons, less the insets.
`protected void`	`installComponents()`	Installs the components.
`protected void`	`installDefaults()`	Installs the defaults.
`protected void`	`installKeyboardActions()`	Installs the keyboard actions.
`protected void`	`installListeners()`	Installs the listeners.
`void`	`installUI(JComponent c)`	Installs the UI.
`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)`	Lays out a horizontal scroll bar.
`protected void`	`layoutVScrollbar(JScrollBar sb)`	Lays out a vertical scroll bar.
`Dimension`	`minimumLayoutSize(Container scrollbarContainer)`	Calculates the minimum size dimensions for the specified container, given the components it contains.
`protected void`	`paintDecreaseHighlight(Graphics g)`	Paints the decrease highlight.
`protected void`	`paintIncreaseHighlight(Graphics g)`	Paints the increase highlight.
`protected void`	`paintThumb(Graphics g, JComponent c, Rectangle thumbBounds)`	Paints the thumb.
`protected void`	`paintTrack(Graphics g, JComponent c, Rectangle trackBounds)`	Paints the track.
`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)`	Scrolls by block.
`protected void`	`scrollByUnit(int direction)`	Scrolls by unit.
`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()`	Uninstalls the components.
`protected void`	`uninstallDefaults()`	Uninstalls the defaults.
`protected void`	`uninstallKeyboardActions()`	Uninstalls the keyboard actions.
`protected void`	`uninstallListeners()`	Uninstall the listeners.
`void`	`uninstallUI(JComponent c)`	Uninstalls the UI.

Methods declared in class ComponentUI

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

Modifier and Type	Method	Description
`boolean`	`contains(JComponent c, int x, int y)`	Returns `true` if the specified x,y location is contained within the look and feel's defined shape of the specified component.
`Accessible`	`getAccessibleChild(JComponent c, int i)`	Returns the `i`th `Accessible` child of the object.
`int`	`getAccessibleChildrenCount(JComponent c)`	Returns the number of accessible children in the object.
`int`	`getBaseline(JComponent c, int width, int height)`	Returns the baseline.
`Component.BaselineResizeBehavior`	`getBaselineResizeBehavior(JComponent c)`	Returns an enum indicating how the baseline of the component changes as the size changes.
`Dimension`	`getMinimumSize(JComponent c)`	Returns the specified component's minimum size appropriate for the look and feel.
`void`	`paint(Graphics g, JComponent c)`	Paints the specified component appropriately for the look and feel.
`void`	`update(Graphics g, JComponent c)`	Notifies this UI delegate that it is time to paint the specified component.

Methods declared in class Object

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

Modifier and Type	Method	Description
`protected Object`	`clone()`	Creates and returns a copy of this object.
`boolean`	`equals(Object obj)`	Indicates whether some other object is "equal to" this one.
`protected void`	`finalize()`	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
`final Class<?>`	`getClass()`	Returns the runtime class of this `Object`.
`int`	`hashCode()`	Returns a hash code value for this object.
`final void`	`notify()`	Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()`	Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()`	Returns a string representation of the object.
`final void`	`wait()`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`	`wait(long timeoutMillis)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis, int nanos)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

Field Details

minimumThumbSize

protected Dimension minimumThumbSize

Minimum thumb size

maximumThumbSize

protected Dimension maximumThumbSize

Maximum thumb size

thumbHighlightColor

protected Color thumbHighlightColor

Thumb highlight color

thumbLightShadowColor

protected Color thumbLightShadowColor

Thumb light shadow color

thumbDarkShadowColor

protected Color thumbDarkShadowColor

Thumb dark shadow color

thumbColor

protected Color thumbColor

Thumb color

trackColor

protected Color trackColor

Track color

trackHighlightColor

protected Color trackHighlightColor

Track highlight color

scrollbar

protected JScrollBar scrollbar

Scrollbar

incrButton

protected JButton incrButton

Increment button

decrButton

protected JButton decrButton

Decrement button

isDragging

protected boolean isDragging

Dragging

trackListener

protected BasicScrollBarUI.TrackListener trackListener

Track listener

buttonListener

protected BasicScrollBarUI.ArrowButtonListener buttonListener

Button listener

modelListener

protected BasicScrollBarUI.ModelListener modelListener

Model listener

thumbRect

protected Rectangle thumbRect

Thumb rectangle

trackRect

protected Rectangle trackRect

Track rectangle

trackHighlight

protected int trackHighlight

Track highlight

NO_HIGHLIGHT

protected static final int NO_HIGHLIGHT

No highlight

See Also:

DECREASE_HIGHLIGHT

protected static final int DECREASE_HIGHLIGHT

Decrease highlight

See Also:

INCREASE_HIGHLIGHT

protected static final int INCREASE_HIGHLIGHT

Increase highlight

See Also:

scrollListener

protected BasicScrollBarUI.ScrollListener scrollListener

Scroll listener

propertyChangeListener

protected PropertyChangeListener propertyChangeListener

Property change listener

scrollTimer

protected Timer scrollTimer

Scroll timer

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 Details

BasicScrollBarUI

public BasicScrollBarUI()

Constructs a BasicScrollBarUI.

Method Details

createUI

public static ComponentUI createUI(JComponent c)

Creates the UI.

Parameters:: c - the component
Returns:: the UI

configureScrollBarColors

protected void configureScrollBarColors()

Configures the scroll bar colors.

installUI

public void installUI(JComponent c)

Installs the UI.

Overrides:

installUI in class ComponentUI

Parameters:

c - the component

See Also:

uninstallUI

public void uninstallUI(JComponent c)

Uninstalls the UI.

Overrides:

uninstallUI in class ComponentUI

Parameters:

c - the component

See Also:

installDefaults

protected void installDefaults()

Installs the defaults.

installComponents

protected void installComponents()

Installs the components.

uninstallComponents

protected void uninstallComponents()

Uninstalls the components.

installListeners

protected void installListeners()

Installs the listeners.

installKeyboardActions

protected void installKeyboardActions()

Installs the keyboard actions.

uninstallKeyboardActions

protected void uninstallKeyboardActions()

Uninstalls the keyboard actions.

uninstallListeners

protected void uninstallListeners()

Uninstall the listeners.

uninstallDefaults

protected void uninstallDefaults()

Uninstalls the defaults.

createTrackListener

protected BasicScrollBarUI.TrackListener createTrackListener()

Creates a track listener.

Returns:: a track listener

createArrowButtonListener

protected BasicScrollBarUI.ArrowButtonListener createArrowButtonListener()

Creates an arrow button listener.

Returns:: an arrow button listener

createModelListener

protected BasicScrollBarUI.ModelListener createModelListener()

Creates a model listener.

Returns:: a model listener

createScrollListener

protected BasicScrollBarUI.ScrollListener createScrollListener()

Creates a scroll listener.

Returns:: a scroll listener

createPropertyChangeListener

protected PropertyChangeListener createPropertyChangeListener()

Creates a property change listener.

Returns:: a property change listener

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

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

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:

createDecreaseButton

protected JButton createDecreaseButton(int orientation)

Creates a decrease button.

Parameters:: orientation - the orientation
Returns:: a decrease button

createIncreaseButton

protected JButton createIncreaseButton(int orientation)

Creates an increase button.

Parameters:: orientation - the orientation
Returns:: an increase button

paintDecreaseHighlight

protected void paintDecreaseHighlight(Graphics g)

Paints the decrease highlight.

Parameters:: g - the graphics

paintIncreaseHighlight

protected void paintIncreaseHighlight(Graphics g)

Paints the increase highlight.

Parameters:: g - the graphics

paintTrack

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

Paints the track.

Parameters:: g - the graphics; c - the component; trackBounds - the track bounds

paintThumb

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

Paints the thumb.

Parameters:: g - the graphics; c - the component; thumbBounds - the thumb bounds

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

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:

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

Returns:

the preferred dimension for the container

See Also:

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

Returns:

the minimum dimension for the container

See Also:

layoutVScrollbar

protected void layoutVScrollbar(JScrollBar sb)

Lays out a vertical scroll bar.

Parameters:: sb - the scroll bar

layoutHScrollbar

protected void layoutHScrollbar(JScrollBar sb)

Lays out a horizontal scroll bar.

Parameters:: sb - the scroll bar

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.

Parameters:

x - set the x location of the thumb

y - set the y location of the thumb

width - set the width of the thumb

height - set the height of the thumb

See Also:

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:

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:

scrollByBlock

protected void scrollByBlock(int direction)

Scrolls by block.

Parameters:: direction - the direction to scroll

scrollByUnit

protected void scrollByUnit(int direction)

Scrolls by unit.

Parameters:: direction - the direction to scroll

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

© 1993, 2025, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.