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# Class java.awt.Scrollbar

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

public class Scrollbar
extends Component
implements Adjustable

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, 64, 0, 255);
>      add(ranger);

Note that the maximum value above, 255, is the maximum value for the scroll bar's bubble. The actual width of the scroll bar's track is 255 + 64. When the scroll bar is set to its maximum value, the left side of the bubble is at 255, and the right side is at 255 + 64.

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 JDK 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 JDK 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`

See Also:
  AdjustmentEvent, AdjustmentListener

##

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

##

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

##

addAdjustmentListener(AdjustmentListener)
  Adds the specified adjustment listener to receive instances of `AdjustmentEvent` from this scroll bar.
addNotify()
  Creates the Scrollbar's peer.
getBlockIncrement()
  Gets the block increment of this scroll bar.
getLineIncrement()
  Deprecated.
getMaximum()
  Gets the maximum value of this scroll bar.
getMinimum()
  Gets the minimum value of this scroll bar.
getOrientation()
  Determines the orientation of this scroll bar.
getPageIncrement()
  Deprecated.
getUnitIncrement()
  Gets the unit increment for this scrollbar.
getValue()
  Gets the current value of this scroll bar.
getVisible()
  Deprecated.
getVisibleAmount()
  Gets the visible amount of this scroll bar.
paramString()
  Returns the parameter string representing the state of this scroll bar.
processAdjustmentEvent(AdjustmentEvent)
  Processes adjustment events occurring on this scrollbar by dispatching them to any registered `AdjustmentListener` objects.
processEvent(AWTEvent)
  Processes events on this scroll bar.
removeAdjustmentListener(AdjustmentListener)
  Removes the specified adjustment listener so that it no longer receives instances of `AdjustmentEvent` from this scroll bar.
setBlockIncrement(int)
  Sets the block increment for this scroll bar.
setLineIncrement(int)
  Deprecated.
setMaximum(int)
  Sets the maximum value of this scroll bar.
setMinimum(int)
  Sets the minimum value of this scroll bar.
setOrientation(int)
  Sets the orientation for this scroll bar.
setPageIncrement(int)
  Deprecated.
setUnitIncrement(int)
  Sets the unit increment for this scroll bar.
setValue(int)
  Sets the value of this scroll bar to the specified value.
setValues(int, int, int, int)
  Sets the values of four properties for this scroll bar.
setVisibleAmount(int)
  Sets the visible amount of this scroll bar.

##

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.

##

Scrollbar

     public Scrollbar()

  Constructs a new vertical scroll bar.

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.

##

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

getOrientation

     public int getOrientation()

  Determines the orientation of this scroll bar.

  Returns:
    the orientation of this scroll bar, either `Scrollbar.HORIZONTAL` or `Scrollbar.VERTICAL`.
  See Also:
    setOrientation

setOrientation

     public synchronized 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.
  See Also:
    getOrientation

getValue

     public int getValue()

  Gets the current value of this scroll bar.

  Returns:
    the current value of this scroll bar.
  See Also:
    getMinimum, getMaximum

setValue

     public synchronized 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.

  Parameters:
    newValue - the new value of the scroll bar.
  See Also:
    setValues, getValue, getMinimum, getMaximum

getMinimum

     public int getMinimum()

  Gets the minimum value of this scroll bar.

  Returns:
    the minimum value of this scroll bar.
  See Also:
    getValue, getMaximum

setMinimum

     public synchronized 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.

  Parameters:
    newMinimum - the new minimum value for this scroll bar.
  See Also:
    setValues, setMaximum

getMaximum

     public int getMaximum()

  Gets the maximum value of this scroll bar.

  Returns:
    the maximum value of this scroll bar.
  See Also:
    getValue, getMinimum

setMaximum

     public synchronized 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.

  Parameters:
    newMaximum - the new maximum value for this scroll bar.
  See Also:
    setValues, setMinimum

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.

  Returns:
    the visible amount of this scroll bar.
  See Also:
    setVisibleAmount

getVisible

     public int getVisible()

  Note: getVisible() is deprecated. As of JDK version 1.1, replaced by `getVisibleAmount()`.

setVisibleAmount

     public synchronized 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.

  Parameters:
    newAmount - the amount visible per page.
  See Also:
    getVisibleAmount, setValues

setUnitIncrement

     public synchronized 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.

  Parameters:
    v - the amount by which to increment or decrement the scroll bar's value.
  See Also:
    getUnitIncrement

setLineIncrement

     public void setLineIncrement(int v)

  Note: setLineIncrement() is 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.

  Returns:
    the unit increment of this scroll bar.
  See Also:
    setUnitIncrement

getLineIncrement

     public int getLineIncrement()

  Note: getLineIncrement() is deprecated. As of JDK version 1.1, replaced by `getUnitIncrement()`.

setBlockIncrement

     public synchronized 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.

  Parameters:
    v - the amount by which to increment or decrement the scroll bar's value.
  See Also:
    getBlockIncrement

setPageIncrement

     public void setPageIncrement(int v)

  Note: setPageIncrement() is 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.

  Returns:
    the block increment of this scroll bar.
  See Also:
    setBlockIncrement

getPageIncrement

     public int getPageIncrement()

  Note: getPageIncrement() is deprecated. As of JDK version 1.1, replaced by `getBlockIncrement()`.

setValues

     public synchronized 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 synchronized void addAdjustmentListener(AdjustmentListener l)

  Adds the specified adjustment listener to receive instances of `AdjustmentEvent` from this scroll bar.

  Parameters:
    l - the adjustment listener.
  See Also:
    AdjustmentEvent, AdjustmentListener, removeAdjustmentListener

removeAdjustmentListener

     public synchronized void removeAdjustmentListener(AdjustmentListener l)

  Removes the specified adjustment listener so that it no longer receives instances of `AdjustmentEvent` from this scroll bar.

  Parameters:
    l - the adjustment listener.
  See Also:
    AdjustmentEvent, AdjustmentListener, addAdjustmentListener

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.

  Parameters:
    e - the event.
  Overrides:
    processEvent in class Component
  See Also:
    AdjustmentEvent, processAdjustmentEvent

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.
  See Also:
    AdjustmentEvent, AdjustmentListener, addAdjustmentListener, enableEvents

paramString

     protected String paramString()

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

  Returns:
    the parameter string of this scroll bar.
  Overrides:
    paramString in class Component

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