JavaTM 2 Platform
Std. Ed. v1.3.1

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:

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.

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:

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

JavaTM 2 Platform
Std. Ed. v1.3.1

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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