public class

JScrollBar

extends JComponent
implements Adjustable Accessible
java.lang.Object
   ↳ java.awt.Component
     ↳ java.awt.Container
       ↳ javax.swing.JComponent
         ↳ javax.swing.JScrollBar
Known Direct Subclasses

Class Overview

An implementation of a scrollbar. The user positions the knob in the scrollbar to determine the contents of the viewing area. The program typically adjusts the display so that the end of the scrollbar represents the end of the displayable contents, or 100% of the contents. The start of the scrollbar is the beginning of the displayable contents, or 0%. The position of the knob within those bounds then translates to the corresponding percentage of the displayable contents.

Typically, as the position of the knob in the scrollbar changes a corresponding change is made to the position of the JViewport on the underlying view, changing the contents of the JViewport.

Warning: Swing is not thread safe. For more information see Swing's Threading Policy.

Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeansTM has been added to the java.beans package. Please see XMLEncoder.

See Also

Summary

Nested Classes
class JScrollBar.AccessibleJScrollBar This class implements accessibility support for the JScrollBar class. 
[Expand]
Inherited Constants
From class javax.swing.JComponent
From class java.awt.Component
From interface java.awt.Adjustable
From interface java.awt.image.ImageObserver
Fields
protected int blockIncrement
protected BoundedRangeModel model The model that represents the scrollbar's minimum, maximum, extent (aka "visibleAmount") and current value.
protected int orientation
protected int unitIncrement
[Expand]
Inherited Fields
From class javax.swing.JComponent
Public Constructors
JScrollBar(int orientation, int value, int extent, int min, int max)
Creates a scrollbar with the specified orientation, value, extent, minimum, and maximum.
JScrollBar(int orientation)
Creates a scrollbar with the specified orientation and the following initial values:
 minimum = 0
 maximum = 100
 value = 0
 extent = 10
 
JScrollBar()
Creates a vertical scrollbar with the following initial values:
 minimum = 0
 maximum = 100
 value = 0
 extent = 10
 
Public Methods
void addAdjustmentListener(AdjustmentListener l)
Adds an AdjustmentListener.
AccessibleContext getAccessibleContext()
Gets the AccessibleContext associated with this JScrollBar.
AdjustmentListener[] getAdjustmentListeners()
Returns an array of all the AdjustmentListeners added to this JScrollBar with addAdjustmentListener().
int getBlockIncrement(int direction)
Returns the amount to change the scrollbar's value by, given a block (usually "page") up/down request.
int getBlockIncrement()
For backwards compatibility with java.awt.Scrollbar.
int getMaximum()
The maximum value of the scrollbar is maximum - extent.
Dimension getMaximumSize()
The scrollbar is flexible along it's scrolling axis and rigid along the other axis.
int getMinimum()
Returns the minimum value supported by the scrollbar (usually zero).
Dimension getMinimumSize()
The scrollbar is flexible along it's scrolling axis and rigid along the other axis.
BoundedRangeModel getModel()
Returns data model that handles the scrollbar's four fundamental properties: minimum, maximum, value, extent.
int getOrientation()
Returns the component's orientation (horizontal or vertical).
ScrollBarUI getUI()
Returns the delegate that implements the look and feel for this component.
String getUIClassID()
Returns the name of the LookAndFeel class for this component.
int getUnitIncrement(int direction)
Returns the amount to change the scrollbar's value by, given a unit up/down request.
int getUnitIncrement()
For backwards compatibility with java.awt.Scrollbar.
int getValue()
Returns the scrollbar's value.
boolean getValueIsAdjusting()
True if the scrollbar knob is being dragged.
int getVisibleAmount()
Returns the scrollbar's extent, aka its "visibleAmount".
void removeAdjustmentListener(AdjustmentListener l)
Removes an AdjustmentEvent listener.
void setBlockIncrement(int blockIncrement)
Sets the blockIncrement property.
void setEnabled(boolean x)
Enables the component so that the knob position can be changed.
void setMaximum(int maximum)
Sets the model's maximum property.
void setMinimum(int minimum)
Sets the model's minimum property.
void setModel(BoundedRangeModel newModel)
Sets the model that handles the scrollbar's four fundamental properties: minimum, maximum, value, extent.
void setOrientation(int orientation)
Set the scrollbar's orientation to either VERTICAL or HORIZONTAL.
void setUI(ScrollBarUI ui)
Sets the L&F object that renders this component.
void setUnitIncrement(int unitIncrement)
Sets the unitIncrement property.
void setValue(int value)
Sets the scrollbar's value.
void setValueIsAdjusting(boolean b)
Sets the model's valueIsAdjusting property.
void setValues(int newValue, int newExtent, int newMin, int newMax)
Sets the four BoundedRangeModel properties after forcing the arguments to obey the usual constraints:
 minimum <= value <= value+extent <= maximum
 

void setVisibleAmount(int extent)
Set the model's extent property.
void updateUI()
Overrides JComponent.updateUI.
Protected Methods
void fireAdjustmentValueChanged(int id, int type, int value)
Notify listeners that the scrollbar's model has changed.
String paramString()
Returns a string representation of this JScrollBar.
[Expand]
Inherited Methods
From class javax.swing.JComponent
From class java.awt.Container
From class java.awt.Component
From class java.lang.Object
From interface java.awt.Adjustable
From interface java.awt.MenuContainer
From interface java.awt.image.ImageObserver
From interface javax.accessibility.Accessible

Fields

protected int blockIncrement

protected BoundedRangeModel model

The model that represents the scrollbar's minimum, maximum, extent (aka "visibleAmount") and current value.

protected int orientation

protected int unitIncrement

Public Constructors

public JScrollBar (int orientation, int value, int extent, int min, int max)

Creates a scrollbar with the specified orientation, value, extent, minimum, and maximum. The "extent" is the size of the viewable area. It is also known as the "visible amount".

Note: Use setBlockIncrement to set the block increment to a size slightly smaller than the view's extent. That way, when the user jumps the knob to an adjacent position, one or two lines of the original contents remain in view.

Throws
IllegalArgumentException if orientation is not one of VERTICAL, HORIZONTAL

public JScrollBar (int orientation)

Creates a scrollbar with the specified orientation and the following initial values:

 minimum = 0
 maximum = 100
 value = 0
 extent = 10
 

public JScrollBar ()

Creates a vertical scrollbar with the following initial values:

 minimum = 0
 maximum = 100
 value = 0
 extent = 10
 

Public Methods

public void addAdjustmentListener (AdjustmentListener l)

Adds an AdjustmentListener. Adjustment listeners are notified each time the scrollbar's model changes. Adjustment events are provided for backwards compatibility with java.awt.Scrollbar.

Note that the AdjustmentEvents type property will always have a placeholder value of AdjustmentEvent.TRACK because all changes to a BoundedRangeModels value are considered equivalent. To change the value of a BoundedRangeModel one just sets its value property, i.e. model.setValue(123). No information about the origin of the change, e.g. it's a block decrement, is provided. We don't try fabricate the origin of the change here.

Parameters
l the AdjustmentLister to add

public AccessibleContext getAccessibleContext ()

Gets the AccessibleContext associated with this JScrollBar. For JScrollBar, the AccessibleContext takes the form of an AccessibleJScrollBar. A new AccessibleJScrollBar instance is created if necessary.

Returns
  • an AccessibleJScrollBar that serves as the AccessibleContext of this JScrollBar

public AdjustmentListener[] getAdjustmentListeners ()

Returns an array of all the AdjustmentListeners added to this JScrollBar with addAdjustmentListener().

Returns
  • all of the AdjustmentListeners added or an empty array if no listeners have been added

public int getBlockIncrement (int direction)

Returns the amount to change the scrollbar's value by, given a block (usually "page") up/down request. A ScrollBarUI implementation typically calls this method when the user clicks above or below the scrollbar "knob" to change the value up or down by large amount. Subclasses my override this method to compute a value, e.g. the change required to scroll up or down one paragraph in a text document.

The JScrollPane component creates scrollbars (by default) that override this method and delegate to the viewports Scrollable view, if it has one. The Scrollable interface provides a more specialized version of this method.

Parameters
direction is -1 or 1 for up/down respectively
Returns
  • the value of the blockIncrement property

public int getBlockIncrement ()

For backwards compatibility with java.awt.Scrollbar.

Returns
  • the block value increment for the adjustable object

public int getMaximum ()

The maximum value of the scrollbar is maximum - extent.

Returns
  • the value of the model's maximum property
See Also

public Dimension getMaximumSize ()

The scrollbar is flexible along it's scrolling axis and rigid along the other axis.

Returns
  • the value of the maximumSize property

public int getMinimum ()

Returns the minimum value supported by the scrollbar (usually zero).

Returns
  • the value of the model's minimum property
See Also

public Dimension getMinimumSize ()

The scrollbar is flexible along it's scrolling axis and rigid along the other axis.

Returns
  • the value of the minimumSize property

public BoundedRangeModel getModel ()

Returns data model that handles the scrollbar's four fundamental properties: minimum, maximum, value, extent.

public int getOrientation ()

Returns the component's orientation (horizontal or vertical).

Returns
  • VERTICAL or HORIZONTAL

public ScrollBarUI getUI ()

Returns the delegate that implements the look and feel for this component.

public String getUIClassID ()

Returns the name of the LookAndFeel class for this component.

Returns
  • "ScrollBarUI"

public int getUnitIncrement (int direction)

Returns the amount to change the scrollbar's value by, given a unit up/down request. A ScrollBarUI implementation typically calls this method when the user clicks on a scrollbar up/down arrow and uses the result to update the scrollbar's value. Subclasses my override this method to compute a value, e.g. the change required to scroll up or down one (variable height) line text or one row in a table.

The JScrollPane component creates scrollbars (by default) that override this method and delegate to the viewports Scrollable view, if it has one. The Scrollable interface provides a more specialized version of this method.

Parameters
direction is -1 or 1 for up/down respectively
Returns
  • the value of the unitIncrement property

public int getUnitIncrement ()

For backwards compatibility with java.awt.Scrollbar.

Returns
  • the unit value increment for the adjustable object

public int getValue ()

Returns the scrollbar's value.

Returns
  • the model's value property
See Also

public boolean getValueIsAdjusting ()

True if the scrollbar knob is being dragged.

Returns
  • the value of the model's valueIsAdjusting property

public int getVisibleAmount ()

Returns the scrollbar's extent, aka its "visibleAmount". In many scrollbar look and feel implementations the size of the scrollbar "knob" or "thumb" is proportional to the extent.

Returns
  • the value of the model's extent property

public void removeAdjustmentListener (AdjustmentListener l)

Removes an AdjustmentEvent listener.

Parameters
l the AdjustmentLister to remove

public void setBlockIncrement (int blockIncrement)

Sets the blockIncrement property.

Note, that if the argument is equal to the value of Integer.MIN_VALUE, the most look and feels will not provide the scrolling to the right/down.

Parameters
blockIncrement the block increment

public void setEnabled (boolean x)

Enables the component so that the knob position can be changed. When the disabled, the knob position cannot be changed.

Parameters
x a boolean value, where true enables the component and false disables it

public void setMaximum (int maximum)

Sets the model's maximum property. Note that the scrollbar's value can only be set to maximum - extent.

Parameters
maximum the maximum value

public void setMinimum (int minimum)

Sets the model's minimum property.

Parameters
minimum the minimum value

public void setModel (BoundedRangeModel newModel)

Sets the model that handles the scrollbar's four fundamental properties: minimum, maximum, value, extent.

See Also

public void setOrientation (int orientation)

Set the scrollbar's orientation to either VERTICAL or HORIZONTAL.

Throws
IllegalArgumentException if orientation is not one of VERTICAL, HORIZONTAL
See Also

public void setUI (ScrollBarUI ui)

Sets the L&F object that renders this component.

Parameters
ui the ScrollBarUI L&F object

public void setUnitIncrement (int unitIncrement)

Sets the unitIncrement property.

Note, that if the argument is equal to the value of Integer.MIN_VALUE, the most look and feels will not provide the scrolling to the right/down.

Parameters
unitIncrement the unit increment

public void setValue (int value)

Sets the scrollbar's value. This method just forwards the value to the model.

Parameters
value the current value, between minimum and maximum - visibleAmount

public void setValueIsAdjusting (boolean b)

Sets the model's valueIsAdjusting property. Scrollbar look and feel implementations should set this property to true when a knob drag begins, and to false when the drag ends. The scrollbar model will not generate ChangeEvents while valueIsAdjusting is true.

public void setValues (int newValue, int newExtent, int newMin, int newMax)

Sets the four BoundedRangeModel properties after forcing the arguments to obey the usual constraints:

 minimum <= value <= value+extent <= maximum
 

public void setVisibleAmount (int extent)

Set the model's extent property.

Parameters
extent the length of the indicator

public void updateUI ()

Overrides JComponent.updateUI.

See Also

Protected Methods

protected void fireAdjustmentValueChanged (int id, int type, int value)

Notify listeners that the scrollbar's model has changed.

protected String paramString ()

Returns a string representation of this JScrollBar. This method is intended to be used only for debugging purposes, and the content and format of the returned string may vary between implementations. The returned string may be empty but may not be null.

Returns
  • a string representation of this JScrollBar.