java.lang.Object | ||
↳ | java.awt.Component | |
↳ | java.awt.Scrollbar |
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" (also called the "thumb" or "scroll box") can be used to 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 in this example is the visible amount. 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 amount
.
In the previous example, because the maximum
is
300 and the visible amount
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 five types of adjustment events 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
Note: We recommend using a Scrollbar
for value selection only. If you want to implement
a scrollable component inside a container, we recommend you use
a ScrollPane
. If you use a
Scrollbar
for this purpose, you are likely to
encounter issues with painting, key handling, sizing and
positioning.
Nested Classes | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Scrollbar.AccessibleAWTScrollBar | This class implements accessibility support for the
Scrollbar class. |
Constants | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
int | HORIZONTAL | A constant that indicates a horizontal scroll bar. | |||||||||
int | VERTICAL | A constant that indicates a vertical scroll bar. |
[Expand]
Inherited Constants | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.awt.Component
| |||||||||||
From interface
java.awt.Adjustable
| |||||||||||
From interface
java.awt.image.ImageObserver
|
Public Constructors | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Constructs a new vertical scroll bar.
| |||||||||||
Constructs a new scroll bar with the specified orientation.
| |||||||||||
Constructs a new scroll bar with the specified orientation,
initial value, visible amount, and minimum and maximum values.
|
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Adds the specified adjustment listener to receive instances of
AdjustmentEvent from this scroll bar. | |||||||||||
Creates the
Scrollbar 's peer. | |||||||||||
Gets the
AccessibleContext associated with this
Scrollbar . | |||||||||||
Returns an array of all the adjustment listeners
registered on this scrollbar.
| |||||||||||
Gets the block increment of this scroll bar.
| |||||||||||
This method is deprecated.
As of JDK version 1.1,
replaced by
getUnitIncrement() .
| |||||||||||
Returns an array of all the objects currently registered
as
FooListener s
upon this Scrollbar . | |||||||||||
Gets the maximum value of this scroll bar.
| |||||||||||
Gets the minimum value of this scroll bar.
| |||||||||||
Returns the orientation of this scroll bar.
| |||||||||||
This method is deprecated.
As of JDK version 1.1,
replaced by
getBlockIncrement() .
| |||||||||||
Gets the unit increment for this scrollbar.
| |||||||||||
Gets the current value of this scroll bar.
| |||||||||||
Returns true if the value is in the process of changing as a
result of actions being taken by the user.
| |||||||||||
This method is deprecated.
As of JDK version 1.1,
replaced by
getVisibleAmount() .
| |||||||||||
Gets the visible amount of this scroll bar.
| |||||||||||
Removes the specified adjustment listener so that it no longer
receives instances of
AdjustmentEvent from this scroll bar. | |||||||||||
Sets the block increment for this scroll bar.
| |||||||||||
This method is deprecated.
As of JDK version 1.1,
replaced by
setUnitIncrement(int) .
| |||||||||||
Sets the maximum value of this scroll bar.
| |||||||||||
Sets the minimum value of this scroll bar.
| |||||||||||
Sets the orientation for this scroll bar.
| |||||||||||
This method is deprecated.
As of JDK version 1.1,
replaced by
setBlockIncrement() .
| |||||||||||
Sets the unit increment for this scroll bar.
| |||||||||||
Sets the value of this scroll bar to the specified value.
| |||||||||||
Sets the
valueIsAdjusting property. | |||||||||||
Sets the values of four properties for this scroll bar:
value , visibleAmount ,
minimum , and maximum . | |||||||||||
Sets the visible amount of this scroll bar.
|
Protected Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Returns a string representing the state of this
Scrollbar . | |||||||||||
Processes adjustment events occurring on this
scrollbar by dispatching them to any registered
AdjustmentListener objects. | |||||||||||
Processes events on this scroll bar.
|
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
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
|
A constant that indicates a horizontal scroll bar.
A constant that indicates a vertical scroll bar.
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 whether the scroll bar is vertical
or horizontal |
Scrollbar.VERTICAL |
value | value which controls the location
of the scroll bar's bubble |
0 |
visible amount | visible amount of the scroll bar's range,
typically represented by the size of the scroll bar's bubble |
10 |
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 |
HeadlessException | if GraphicsEnvironment.isHeadless() returns true. |
---|
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.
orientation | indicates the orientation of the scroll bar |
---|
IllegalArgumentException | when an illegal value for
the orientation argument is supplied |
---|---|
HeadlessException | if GraphicsEnvironment.isHeadless() returns true. |
Constructs a new scroll bar with the specified orientation, initial value, visible amount, 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.
The parameters supplied to this constructor are subject to the
constraints described in setValues(int, int, int, int)
.
orientation | indicates the orientation of the scroll bar. |
---|---|
value | the initial value of the scroll bar |
visible | the visible amount of the scroll bar, typically represented by the size of the bubble |
minimum | the minimum value of the scroll bar |
maximum | the maximum value of the scroll bar |
IllegalArgumentException | when an illegal value for
the orientation argument is supplied |
---|---|
HeadlessException | if GraphicsEnvironment.isHeadless() returns true. |
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.
Refer to AWT Threading Issues for details on AWT's threading model.
l | the adjustment listener |
---|
Creates the Scrollbar
's peer. The peer allows you to modify
the appearance of the Scrollbar
without changing any of its
functionality.
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.
AccessibleAWTScrollBar
that serves as the
AccessibleContext
of this ScrollBar
Returns an array of all the adjustment listeners registered on this scrollbar.
AdjustmentListener
s
or an empty array if no adjustment
listeners are currently registeredGets the block increment of this scroll bar.
The block increment is the value that is added or 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. The block increment must be greater than zero.
This method is deprecated.
As of JDK version 1.1,
replaced by getUnitIncrement()
.
Returns an array of all the objects currently registered
as FooListener
s
upon this Scrollbar
.
FooListener
s are registered using the
addFooListener
method.
You can specify the listenerType
argument
with a class literal, such as
FooListener.class
.
For example, you can query a
Scrollbar
c
for its mouse listeners with the following code:
MouseListener[] mls = (MouseListener[])(c.getListeners(MouseListener.class));If no such listeners exist, this method returns an empty array.
listenerType | the type of listeners requested; this parameter
should specify an interface that descends from
java.util.EventListener |
---|
FooListener
s on this component,
or an empty array if no such listeners have been addedClassCastException | if listenerType
doesn't specify a class or interface that implements
java.util.EventListener |
---|
Gets the maximum value of this scroll bar.
Gets the minimum value of this scroll bar.
Returns the orientation of this scroll bar.
Scrollbar.HORIZONTAL
or
Scrollbar.VERTICAL
This method is deprecated.
As of JDK version 1.1,
replaced by getBlockIncrement()
.
Gets the unit increment for this scrollbar.
The unit increment is the value that is added or 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. The unit increment must be greater than zero.
Gets the current value of this scroll bar.
Returns true if the value is in the process of changing as a result of actions being taken by the user.
valueIsAdjusting
property
This method is deprecated.
As of JDK version 1.1,
replaced by getVisibleAmount()
.
Gets the visible amount of this scroll bar.
When a scroll bar is used to select a range of values, the visible amount is used to represent the range of values that are currently visible. The size of the scroll bar's bubble (also called a thumb or scroll box), usually gives a visual representation of the relationship of the visible amount to the range of the scroll bar.
The scroll bar's bubble may not be displayed when it is not
moveable (e.g. when it takes up the entire length of the
scroll bar's track, or when the scroll bar is disabled).
Whether the bubble is displayed or not will not affect
the value returned by getVisibleAmount
.
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.
Refer to AWT Threading Issues for details on AWT's threading model.
l | the adjustment listener |
---|
Sets the block increment for this scroll bar.
The block increment is the value that is added or 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. The block increment must be greater than zero. Attepts to set the block increment to a value lower than 1 will result in a value of 1 being set.
v | the amount by which to increment or decrement the scroll bar's value |
---|
This method is deprecated.
As of JDK version 1.1,
replaced by setUnitIncrement(int)
.
Sets the maximum value of this scroll bar.
When setMaximum
is called, the maximum value
is changed, and other values (including the minimum, the
visible amount, and the current scroll bar value)
are changed to be consistent with the new maximum.
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.
Note that setting the maximum value to Integer.MIN_VALUE
will result in the new maximum value being set to
Integer.MIN_VALUE + 1
.
newMaximum | the new maximum value for this scroll bar |
---|
Sets the minimum value of this scroll bar.
When setMinimum
is called, the minimum value
is changed, and other values (including the maximum, the
visible amount, and the current scroll bar value)
are changed to be consistent with the new minimum.
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.
Note that setting the minimum value to Integer.MAX_VALUE
will result in the new minimum value being set to
Integer.MAX_VALUE - 1
.
newMinimum | the new minimum value for this scroll bar |
---|
Sets the orientation for this scroll bar.
orientation | the orientation of this scroll bar, either
Scrollbar.HORIZONTAL or
Scrollbar.VERTICAL |
---|
IllegalArgumentException | if the value supplied
for orientation is not a
legal value |
---|
This method is deprecated.
As of JDK version 1.1,
replaced by setBlockIncrement()
.
Sets the unit increment for this scroll bar.
The unit increment is the value that is added or 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. The unit increment must be greater than zero. Attepts to set the unit increment to a value lower than 1 will result in a value of 1 being set.
v | the amount by which to increment or decrement the scroll bar's value |
---|
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 - visibleAmount
,
then either minimum
or maximum - visibleAmount
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.
Calling this method does not fire an
AdjustmentEvent
.
newValue | the new value of the scroll bar |
---|
Sets the valueIsAdjusting
property.
b | new adjustment-in-progress status |
---|
Sets the values of four properties for this scroll bar:
value
, visibleAmount
,
minimum
, and maximum
.
If the values supplied for these properties are inconsistent
or incorrect, they will be changed to ensure consistency.
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
following constraints:
maximum
must be greater than minimum
,
maximum - minimum
must not be greater
than Integer.MAX_VALUE
,
visibleAmount
must be greater than zero.
visibleAmount
must not be greater than
maximum - minimum
,
value
must not be less than minimum
,
and value
must not be greater than
maximum - visibleAmount
Calling this method does not fire an
AdjustmentEvent
.
value | is the position in the current window |
---|---|
visible | is the visible amount of the scroll bar |
minimum | is the minimum value of the scroll bar |
maximum | is the maximum value of the scroll bar |
Sets the visible amount of this scroll bar.
When a scroll bar is used to select a range of values, the visible amount is used to represent the range of values that are currently visible. The size of the scroll bar's bubble (also called a thumb or scroll box), usually gives a visual representation of the relationship of the visible amount to the range of the scroll bar.
The scroll bar's bubble may not be displayed when it is not
moveable (e.g. when it takes up the entire length of the
scroll bar's track, or when the scroll bar is disabled).
Whether the bubble is displayed or not will not affect
the value returned by getVisibleAmount
.
If the visible amount supplied is less than one
or greater than the current maximum - minimum
,
then either one
or maximum - minimum
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.
newAmount | the new visible amount |
---|
Returns a string representing the state of this Scrollbar
.
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
.
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:
AdjustmentListener
object is registered
via addAdjustmentListener
.
enableEvents
.
Note that if the event parameter is null
the behavior is unspecified and may result in an
exception.
e | the adjustment event |
---|
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.
Note that if the event parameter is null
the behavior is unspecified and may result in an
exception.
e | the event |
---|