java.awt
Class Scrollbar

java.lang.Object
  |
  +--java.awt.Component
        |
        +--java.awt.Scrollbar

All Implemented Interfaces:

Accessible, Adjustable, ImageObserver, MenuContainer, Serializable

public class Scrollbar

extends Component

implements Adjustable, Accessible

The Scrollbar class embodies a scroll bar, a familiar user-interface object. A scroll bar provides a convenient means for allowing a user to select from a range of values. The following three vertical scroll bars could be used as slider controls to pick the red, green, and blue components of a color:

Each scroll bar in this example could be created with code similar to the following:

 redSlider=new Scrollbar(Scrollbar.VERTICAL, 0, 1, 0, 255);
 add(redSlider);
 

Alternatively, a scroll bar can represent a range of values. For example, if a scroll bar is used for scrolling through text, the width of the "bubble" or "thumb" can represent the amount of text that is visible. Here is an example of a scroll bar that represents a range:

The value range represented by the bubble is the visible range of the scroll bar. The horizontal scroll bar in this example could be created with code like the following:

 ranger = new Scrollbar(Scrollbar.HORIZONTAL, 0, 60, 0, 300);
 add(ranger);
 

Note that the actual maximum value of the scroll bar is the maximum minus the visible. In the previous example, because the maximum is 300 and the visible is 60, the actual maximum value is 240. The range of the scrollbar track is 0 - 300. The left side of the bubble indicates the value of the scroll bar.

Normally, the user changes the value of the scroll bar by making a gesture with the mouse. For example, the user can drag the scroll bar's bubble up and down, or click in the scroll bar's unit increment or block increment areas. Keyboard gestures can also be mapped to the scroll bar. By convention, the Page Up and Page Down keys are equivalent to clicking in the scroll bar's block increment and block decrement areas.

When the user changes the value of the scroll bar, the scroll bar receives an instance of AdjustmentEvent. The scroll bar processes this event, passing it along to any registered listeners.

Any object that wishes to be notified of changes to the scroll bar's value should implement AdjustmentListener, an interface defined in the package java.awt.event. Listeners can be added and removed dynamically by calling the methods addAdjustmentListener and removeAdjustmentListener.

The AdjustmentEvent class defines five types of adjustment event, listed here:

• AdjustmentEvent.TRACK is sent out when the user drags the scroll bar's bubble.
• AdjustmentEvent.UNIT_INCREMENT is sent out when the user clicks in the left arrow of a horizontal scroll bar, or the top arrow of a vertical scroll bar, or makes the equivalent gesture from the keyboard.
• AdjustmentEvent.UNIT_DECREMENT is sent out when the user clicks in the right arrow of a horizontal scroll bar, or the bottom arrow of a vertical scroll bar, or makes the equivalent gesture from the keyboard.
• AdjustmentEvent.BLOCK_INCREMENT is sent out when the user clicks in the track, to the left of the bubble on a horizontal scroll bar, or above the bubble on a vertical scroll bar. By convention, the Page Up key is equivalent, if the user is using a keyboard that defines a Page Up key.
• AdjustmentEvent.BLOCK_DECREMENT is sent out when the user clicks in the track, to the right of the bubble on a horizontal scroll bar, or below the bubble on a vertical scroll bar. By convention, the Page Down key is equivalent, if the user is using a keyboard that defines a Page Down key.

The JDK 1.0 event system is supported for backwards compatibility, but its use with newer versions of the platform is discouraged. The fives types of adjustment event introduced with JDK 1.1 correspond to the five event types that are associated with scroll bars in previous platform versions. The following list gives the adjustment event type, and the corresponding JDK 1.0 event type it replaces.

• AdjustmentEvent.TRACK replaces Event.SCROLL_ABSOLUTE
• AdjustmentEvent.UNIT_INCREMENT replaces Event.SCROLL_LINE_UP
• AdjustmentEvent.UNIT_DECREMENT replaces Event.SCROLL_LINE_DOWN
• AdjustmentEvent.BLOCK_INCREMENT replaces Event.SCROLL_PAGE_UP
• AdjustmentEvent.BLOCK_DECREMENT replaces Event.SCROLL_PAGE_DOWN

Since:

JDK1.0

See Also:

AdjustmentEvent, AdjustmentListener, Serialized Form

Inner Class Summary

protected class

Scrollbar.AccessibleAWTScrollBar This class implements accessibility support for the Scrollbar class.

Inner classes inherited from class java.awt.Component

Component.AccessibleAWTComponent

Field Summary

static int	HORIZONTAL A constant that indicates a horizontal scroll bar.
static int	VERTICAL A constant that indicates a vertical scroll bar.

Fields inherited from class java.awt.Component

BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

Fields inherited from interface java.awt.image.ImageObserver

ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH

Constructor Summary

Scrollbar()
Constructs a new vertical scroll bar.

Scrollbar(int orientation)
Constructs a new scroll bar with the specified orientation.

Scrollbar(int orientation, int value, int visible, int minimum, int maximum)
Constructs a new scroll bar with the specified orientation, initial value, page size, and minimum and maximum values.

Method Summary

void	addAdjustmentListener(AdjustmentListener l) Adds the specified adjustment listener to receive instances of AdjustmentEvent from this scroll bar.
void	addNotify() Creates the Scrollbar's peer.
AccessibleContext	getAccessibleContext() Gets the AccessibleContext associated with this Scrollbar.
int	getBlockIncrement() Gets the block increment of this scroll bar.
int	getLineIncrement() Deprecated. As of JDK version 1.1, replaced by getUnitIncrement().
EventListener[]	getListeners(Class listenerType) Return an array of all the listeners that were added to the Scrollbar with addXXXListener(), where XXX is the name of the listenerType argument.
int	getMaximum() Gets the maximum value of this scroll bar.
int	getMinimum() Gets the minimum value of this scroll bar.
int	getOrientation() Determines the orientation of this scroll bar.
int	getPageIncrement() Deprecated. As of JDK version 1.1, replaced by getBlockIncrement().
int	getUnitIncrement() Gets the unit increment for this scrollbar.
int	getValue() Gets the current value of this scroll bar.
int	getVisible() Deprecated. As of JDK version 1.1, replaced by getVisibleAmount().
int	getVisibleAmount() Gets the visible amount of this scroll bar.
protected String	paramString() Returns the parameter string representing the state of this scroll bar.
protected void	processAdjustmentEvent(AdjustmentEvent e) Processes adjustment events occurring on this scrollbar by dispatching them to any registered AdjustmentListener objects.
protected void	processEvent(AWTEvent e) Processes events on this scroll bar.
void	removeAdjustmentListener(AdjustmentListener l) Removes the specified adjustment listener so that it no longer receives instances of AdjustmentEvent from this scroll bar.
void	setBlockIncrement(int v) Sets the block increment for this scroll bar.
void	setLineIncrement(int v) Deprecated. As of JDK version 1.1, replaced by setUnitIncrement(int).
void	setMaximum(int newMaximum) Sets the maximum value of this scroll bar.
void	setMinimum(int newMinimum) Sets the minimum value of this scroll bar.
void	setOrientation(int orientation) Sets the orientation for this scroll bar.
void	setPageIncrement(int v) Deprecated. As of JDK version 1.1, replaced by setBlockIncrement().
void	setUnitIncrement(int v) Sets the unit increment for this scroll bar.
void	setValue(int newValue) Sets the value of this scroll bar to the specified value.
void	setValues(int value, int visible, int minimum, int maximum) Sets the values of four properties for this scroll bar.
void	setVisibleAmount(int newAmount) Sets the visible amount of this scroll bar.

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addPropertyChangeListener, addPropertyChangeListener, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentOrientation, getCursor, getDropTarget, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getInputContext, getInputMethodRequests, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getMinimumSize, getName, getParent, getPeer, getPreferredSize, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, invalidate, isDisplayable, isDoubleBuffered, isEnabled, isFocusTraversable, isLightweight, isOpaque, isShowing, isValid, isVisible, keyDown, keyUp, layout, list, list, list, list, list, locate, location, lostFocus, minimumSize, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paint, paintAll, postEvent, preferredSize, prepareImage, prepareImage, print, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, reshape, resize, resize, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFont, setForeground, setLocale, setLocation, setLocation, setName, setSize, setSize, setVisible, show, show, size, toString, transferFocus, update, validate

Methods inherited from class java.lang.Object

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

Field Detail

HORIZONTAL

public static final int HORIZONTAL

A constant that indicates a horizontal scroll bar.

VERTICAL

public static final int VERTICAL

A constant that indicates a vertical scroll bar.

Constructor Detail

Scrollbar

public Scrollbar()

Constructs a new vertical scroll bar. The default properties of the scroll bar are listed in the following table:

Property	Description	Default Value
orientation	indicates if the scroll bar is vertical or horizontal	Scrollbar.VERTICAL
value	value which controls the location of the scroll bar bubble	0
minimum	minimum value of the scroll bar	0
maximum	maximum value of the scroll bar	100
unit increment	amount the value changes when the Line Up or Line Down key is pressed, or when the end arrows of the scrollbar are clicked	1
block increment	amount the value changes when the Page Up or Page Down key is pressed, or when the scrollbar track is clicked on either side of the bubble	10

Scrollbar

public Scrollbar(int orientation)

Constructs a new scroll bar with the specified orientation.

The orientation argument must take one of the two values Scrollbar.HORIZONTAL, or Scrollbar.VERTICAL, indicating a horizontal or vertical scroll bar, respectively.

Parameters:

orientation - indicates the orientation of the scroll bar.

Throws:

IllegalArgumentException - when an illegal value for the orientation argument is supplied.

Scrollbar

public Scrollbar(int orientation,
                 int value,
                 int visible,
                 int minimum,
                 int maximum)

Constructs a new scroll bar with the specified orientation, initial value, page size, and minimum and maximum values.

The orientation argument must take one of the two values Scrollbar.HORIZONTAL, or Scrollbar.VERTICAL, indicating a horizontal or vertical scroll bar, respectively.

If the specified maximum value is less than the minimum value, it is changed to be the same as the minimum value. If the initial value is lower than the minimum value, it is changed to be the minimum value; if it is greater than the maximum value, it is changed to be the maximum value.

Parameters:

orientation - indicates the orientation of the scroll bar.

value - the initial value of the scroll bar.

visible - the size of the scroll bar's bubble, representing the visible portion; the scroll bar uses this value when paging up or down by a page.

minimum - the minimum value of the scroll bar.

maximum - the maximum value of the scroll bar.

Method Detail

addNotify

public void addNotify()

Creates the Scrollbar's peer. The peer allows you to modify the appearance of the Scrollbar without changing any of its functionality.

Overrides:

addNotify in class Component

Following copied from class: java.awt.Component

See Also:

Component.isDisplayable(), Component.removeNotify()

getOrientation

public int getOrientation()

Determines the orientation of this scroll bar.

Specified by:

getOrientation in interface Adjustable

Returns:

the orientation of this scroll bar, either Scrollbar.HORIZONTAL or Scrollbar.VERTICAL.

See Also:

setOrientation(int)

setOrientation

public void setOrientation(int orientation)

Sets the orientation for this scroll bar.

Parameters:

the - orientation of this scroll bar, either Scrollbar.HORIZONTAL or Scrollbar.VERTICAL.

Throws:

IllegalArgumentException - if the value supplied for orientation is not a legal value.

Since:

JDK1.1

See Also:

getOrientation()

getValue

public int getValue()

Gets the current value of this scroll bar.

Specified by:

getValue in interface Adjustable

Returns:

the current value of this scroll bar.

See Also:

getMinimum(), getMaximum()

setValue

public void setValue(int newValue)

Sets the value of this scroll bar to the specified value.

If the value supplied is less than the current minimum or greater than the current maximum, then one of those values is substituted, as appropriate.

Normally, a program should change a scroll bar's value only by calling setValues. The setValues method simultaneously and synchronously sets the minimum, maximum, visible amount, and value properties of a scroll bar, so that they are mutually consistent.

Specified by:

setValue in interface Adjustable

Parameters:

newValue - the new value of the scroll bar.

See Also:

setValues(int, int, int, int), getValue(), getMinimum(), getMaximum()

getMinimum

public int getMinimum()

Gets the minimum value of this scroll bar.

Specified by:

getMinimum in interface Adjustable

Returns:

the minimum value of this scroll bar.

See Also:

getValue(), getMaximum()

setMinimum

public void setMinimum(int newMinimum)

Sets the minimum value of this scroll bar.

Normally, a program should change a scroll bar's minimum value only by calling setValues. The setValues method simultaneously and synchronously sets the minimum, maximum, visible amount, and value properties of a scroll bar, so that they are mutually consistent.

Specified by:

setMinimum in interface Adjustable

Parameters:

newMinimum - the new minimum value for this scroll bar.

Since:

JDK1.1

See Also:

setValues(int, int, int, int), setMaximum(int)

getMaximum

public int getMaximum()

Gets the maximum value of this scroll bar.

Specified by:

getMaximum in interface Adjustable

Returns:

the maximum value of this scroll bar.

See Also:

getValue(), getMinimum()

setMaximum

public void setMaximum(int newMaximum)

Sets the maximum value of this scroll bar.

Normally, a program should change a scroll bar's maximum value only by calling setValues. The setValues method simultaneously and synchronously sets the minimum, maximum, visible amount, and value properties of a scroll bar, so that they are mutually consistent.

Specified by:

setMaximum in interface Adjustable

Parameters:

newMaximum - the new maximum value for this scroll bar.

Since:

JDK1.1

See Also:

setValues(int, int, int, int), setMinimum(int)

getVisibleAmount

public int getVisibleAmount()

Gets the visible amount of this scroll bar.

The visible amount of a scroll bar is the range of values represented by the width of the scroll bar's bubble. It is used to determine the scroll bar's block increment.

Specified by:

getVisibleAmount in interface Adjustable

Returns:

the visible amount of this scroll bar.

Since:

JDK1.1

See Also:

setVisibleAmount(int)

getVisible

public int getVisible()

Deprecated. As of JDK version 1.1, replaced by getVisibleAmount().

setVisibleAmount

public void setVisibleAmount(int newAmount)

Sets the visible amount of this scroll bar.

The visible amount of a scroll bar is the range of values represented by the width of the scroll bar's bubble. It is used to determine the scroll bar's block increment.

Normally, a program should change a scroll bar's value only by calling setValues. The setValues method simultaneously and synchronously sets the minimum, maximum, visible amount, and value properties of a scroll bar, so that they are mutually consistent.

Specified by:

setVisibleAmount in interface Adjustable

Parameters:

newAmount - the amount visible per page.

Since:

JDK1.1

See Also:

getVisibleAmount(), setValues(int, int, int, int)

setUnitIncrement

public void setUnitIncrement(int v)

Sets the unit increment for this scroll bar.

The unit increment is the value that is added (subtracted) when the user activates the unit increment area of the scroll bar, generally through a mouse or keyboard gesture that the scroll bar receives as an adjustment event.

Specified by:

setUnitIncrement in interface Adjustable

Parameters:

v - the amount by which to increment or decrement the scroll bar's value.

Since:

JDK1.1

See Also:

getUnitIncrement()

setLineIncrement

public void setLineIncrement(int v)

Deprecated. As of JDK version 1.1, replaced by setUnitIncrement(int).

getUnitIncrement

public int getUnitIncrement()

Gets the unit increment for this scrollbar.

The unit increment is the value that is added (subtracted) when the user activates the unit increment area of the scroll bar, generally through a mouse or keyboard gesture that the scroll bar receives as an adjustment event.

Specified by:

getUnitIncrement in interface Adjustable

Returns:

the unit increment of this scroll bar.

Since:

JDK1.1

See Also:

setUnitIncrement(int)

getLineIncrement

public int getLineIncrement()

Deprecated. As of JDK version 1.1, replaced by getUnitIncrement().

setBlockIncrement

public void setBlockIncrement(int v)

Sets the block increment for this scroll bar.

The block increment is the value that is added (subtracted) when the user activates the block increment area of the scroll bar, generally through a mouse or keyboard gesture that the scroll bar receives as an adjustment event.

Specified by:

setBlockIncrement in interface Adjustable

Parameters:

v - the amount by which to increment or decrement the scroll bar's value.

Since:

JDK1.1

See Also:

getBlockIncrement()

setPageIncrement

public void setPageIncrement(int v)

Deprecated. As of JDK version 1.1, replaced by setBlockIncrement().

getBlockIncrement

public int getBlockIncrement()

Gets the block increment of this scroll bar.

The block increment is the value that is added (subtracted) when the user activates the block increment area of the scroll bar, generally through a mouse or keyboard gesture that the scroll bar receives as an adjustment event.

Specified by:

getBlockIncrement in interface Adjustable

Returns:

the block increment of this scroll bar.

Since:

JDK1.1

See Also:

setBlockIncrement(int)

getPageIncrement

public int getPageIncrement()

Deprecated. As of JDK version 1.1, replaced by getBlockIncrement().

setValues

public void setValues(int value,
                      int visible,
                      int minimum,
                      int maximum)

Sets the values of four properties for this scroll bar.

This method simultaneously and synchronously sets the values of four scroll bar properties, assuring that the values of these properties are mutually consistent. It enforces the constraints that maximum cannot be less than minimum, and that value cannot be less than the minimum or greater than the maximum.

Parameters:

value - is the position in the current window.

visible - is the amount visible per page.

minimum - is the minimum value of the scroll bar.

maximum - is the maximum value of the scroll bar.

addAdjustmentListener

public void addAdjustmentListener(AdjustmentListener l)

Adds the specified adjustment listener to receive instances of AdjustmentEvent from this scroll bar. If l is null, no exception is thrown and no action is performed.

Specified by:

addAdjustmentListener in interface Adjustable

Parameters:

l - the adjustment listener.

Since:

JDK1.1

See Also:

AdjustmentEvent, AdjustmentListener, removeAdjustmentListener(java.awt.event.AdjustmentListener)

removeAdjustmentListener

public void removeAdjustmentListener(AdjustmentListener l)

Removes the specified adjustment listener so that it no longer receives instances of AdjustmentEvent from this scroll bar. If l is null, no exception is thrown and no action is performed.

Specified by:

removeAdjustmentListener in interface Adjustable

Parameters:

l - the adjustment listener.

Since:

JDK1.1

See Also:

AdjustmentEvent, AdjustmentListener, addAdjustmentListener(java.awt.event.AdjustmentListener)

getListeners

public EventListener[] getListeners(Class listenerType)

Return an array of all the listeners that were added to the Scrollbar with addXXXListener(), where XXX is the name of the listenerType argument. For example, to get all of the AdjustmentListener(s) for the given Scrollbar s, one would write:

 AdjustmentListener[] als = (AdjustmentListener[])(s.getListeners(AdjustmentListener.class))
 

If no such listener list exists, then an empty array is returned.

Overrides:

getListeners in class Component

Parameters:

listenerType - Type of listeners requested

Returns:

all of the listeners of the specified type supported by this scrollbar

Since:

1.3

processEvent

protected void processEvent(AWTEvent e)

Processes events on this scroll bar. If the event is an instance of AdjustmentEvent, it invokes the processAdjustmentEvent method. Otherwise, it invokes its superclass's processEvent method.

Overrides:

processEvent in class Component

Parameters:

e - the event.

Since:

JDK1.1

See Also:

AdjustmentEvent, processAdjustmentEvent(java.awt.event.AdjustmentEvent)

processAdjustmentEvent

protected void processAdjustmentEvent(AdjustmentEvent e)

Processes adjustment events occurring on this scrollbar by dispatching them to any registered AdjustmentListener objects.

This method is not called unless adjustment events are enabled for this component. Adjustment events are enabled when one of the following occurs:

• An AdjustmentListener object is registered via addAdjustmentListener.
• Adjustment events are enabled via enableEvents.

Parameters:

e - the adjustment event.

Since:

JDK1.1

See Also:

AdjustmentEvent, AdjustmentListener, addAdjustmentListener(java.awt.event.AdjustmentListener), Component.enableEvents(long)

paramString

protected String paramString()

Returns the parameter string representing the state of this scroll bar. This string is useful for debugging.

Overrides:

paramString in class Component

Returns:

the parameter string of this scroll bar.

getAccessibleContext

public AccessibleContext getAccessibleContext()

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

Specified by:

getAccessibleContext in interface Accessible

Overrides:

getAccessibleContext in class Component

Returns:

an AccessibleAWTScrollBar that serves as the AccessibleContext of this ScrollBar