Scrollbar
Class Scrollbar
- java.lang.Object
-
- java.awt.Component
-
- java.awt.Scrollbar
- All Implemented Interfaces:
- Adjustable, ImageObserver, MenuContainer, Serializable, Accessible
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" (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
replacesEvent.SCROLL_ABSOLUTE
-
AdjustmentEvent.UNIT_INCREMENT
replacesEvent.SCROLL_LINE_UP
-
AdjustmentEvent.UNIT_DECREMENT
replacesEvent.SCROLL_LINE_DOWN
-
AdjustmentEvent.BLOCK_INCREMENT
replacesEvent.SCROLL_PAGE_UP
-
AdjustmentEvent.BLOCK_DECREMENT
replacesEvent.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.
- Since:
- JDK1.0
- See Also:
-
AdjustmentEvent
,AdjustmentListener
, Serialized Form
Nested Classes
Modifier and Type | Class and Description |
---|---|
protected class |
Scrollbar.AccessibleAWTScrollBar This class implements accessibility support for the |
Nested classes/interfaces inherited from class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy
Fields
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.
Constructors
Scrollbar
public Scrollbar() throws HeadlessException
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 |
- Throws:
-
HeadlessException
- if GraphicsEnvironment.isHeadless() returns true. - See Also:
GraphicsEnvironment.isHeadless()
Scrollbar
public Scrollbar(int orientation) throws HeadlessException
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 theorientation
argument is supplied -
HeadlessException
- if GraphicsEnvironment.isHeadless() returns true. - See Also:
GraphicsEnvironment.isHeadless()
Scrollbar
public Scrollbar(int orientation, int value, int visible, int minimum, int maximum) throws HeadlessException
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)
.
- Parameters:
-
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 - Throws:
-
IllegalArgumentException
- when an illegal value for theorientation
argument is supplied -
HeadlessException
- if GraphicsEnvironment.isHeadless() returns true. - See Also:
-
setValues(int, int, int, int)
,GraphicsEnvironment.isHeadless()
Methods
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 classComponent
- See Also:
-
Component.isDisplayable()
,Component.removeNotify()
,Component.invalidate()
getOrientation
public int getOrientation()
Returns the orientation of this scroll bar.
- Specified by:
-
getOrientation
in interfaceAdjustable
- Returns:
- the orientation of this scroll bar, either
Scrollbar.HORIZONTAL
orScrollbar.VERTICAL
- See Also:
setOrientation(int)
setOrientation
public void setOrientation(int orientation)
Sets the orientation for this scroll bar.
- Parameters:
-
orientation
- the orientation of this scroll bar, eitherScrollbar.HORIZONTAL
orScrollbar.VERTICAL
- Throws:
-
IllegalArgumentException
- if the value supplied fororientation
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 interfaceAdjustable
- 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 - 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
.
- Specified by:
-
setValue
in interfaceAdjustable
- 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 interfaceAdjustable
- 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.
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
.
- Specified by:
-
setMinimum
in interfaceAdjustable
- 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 interfaceAdjustable
- 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.
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
.
- Specified by:
-
setMaximum
in interfaceAdjustable
- 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.
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. Note that depending on platform, the value of the visible amount property may not be visually indicated by the size of the bubble.
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
.
- Specified by:
-
getVisibleAmount
in interfaceAdjustable
- Returns:
- the visible amount of this scroll bar
- Since:
- JDK1.1
- See Also:
setVisibleAmount(int)
getVisible
@Deprecated 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.
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. Note that depending on platform, the value of the visible amount property may not be visually indicated by the size of the bubble.
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.
- Specified by:
-
setVisibleAmount
in interfaceAdjustable
- Parameters:
-
newAmount
- the new visible amount - 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 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.
In some operating systems, this property can be ignored by the underlying controls.
- Specified by:
-
setUnitIncrement
in interfaceAdjustable
- Parameters:
-
v
- the amount by which to increment or decrement the scroll bar's value - Since:
- JDK1.1
- See Also:
getUnitIncrement()
setLineIncrement
@Deprecated 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 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.
In some operating systems, this property can be ignored by the underlying controls.
- Specified by:
-
getUnitIncrement
in interfaceAdjustable
- Returns:
- the unit increment of this scroll bar
- Since:
- JDK1.1
- See Also:
setUnitIncrement(int)
getLineIncrement
@Deprecated 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 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.
- Specified by:
-
setBlockIncrement
in interfaceAdjustable
- Parameters:
-
v
- the amount by which to increment or decrement the scroll bar's value - Since:
- JDK1.1
- See Also:
getBlockIncrement()
setPageIncrement
@Deprecated 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 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.
- Specified by:
-
getBlockIncrement
in interfaceAdjustable
- Returns:
- the block increment of this scroll bar
- Since:
- JDK1.1
- See Also:
setBlockIncrement(int)
getPageIncrement
@Deprecated 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: 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
.
- Parameters:
-
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 - See Also:
-
setMinimum(int)
,setMaximum(int)
,setVisibleAmount(int)
,setValue(int)
getValueIsAdjusting
public boolean getValueIsAdjusting()
Returns true if the value is in the process of changing as a result of actions being taken by the user.
- Returns:
- the value of the
valueIsAdjusting
property - Since:
- 1.4
- See Also:
setValueIsAdjusting(boolean)
setValueIsAdjusting
public void setValueIsAdjusting(boolean b)
Sets the valueIsAdjusting
property.
- Parameters:
-
b
- new adjustment-in-progress status - Since:
- 1.4
- See Also:
getValueIsAdjusting()
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.
Refer to AWT Threading Issues for details on AWT's threading model.
- Specified by:
-
addAdjustmentListener
in interfaceAdjustable
- Parameters:
-
l
- the adjustment listener - Since:
- JDK1.1
- See Also:
-
removeAdjustmentListener(java.awt.event.AdjustmentListener)
,getAdjustmentListeners()
,AdjustmentEvent
,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.
Refer to AWT Threading Issues for details on AWT's threading model.
- Specified by:
-
removeAdjustmentListener
in interfaceAdjustable
- Parameters:
-
l
- the adjustment listener - Since:
- JDK1.1
- See Also:
-
addAdjustmentListener(java.awt.event.AdjustmentListener)
,getAdjustmentListeners()
,AdjustmentEvent
,AdjustmentListener
getAdjustmentListeners
public AdjustmentListener[] getAdjustmentListeners()
Returns an array of all the adjustment listeners registered on this scrollbar.
- Returns:
- all of this scrollbar's
AdjustmentListener
s or an empty array if no adjustment listeners are currently registered - Since:
- 1.4
- See Also:
-
addAdjustmentListener(java.awt.event.AdjustmentListener)
,removeAdjustmentListener(java.awt.event.AdjustmentListener)
,AdjustmentEvent
,AdjustmentListener
getListeners
public <T extends EventListener> T[] getListeners(Class<T> listenerType)
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.
- Overrides:
-
getListeners
in classComponent
- Parameters:
-
listenerType
- the type of listeners requested; this parameter should specify an interface that descends fromjava.util.EventListener
- Returns:
- an array of all objects registered as
FooListener
s on this component, or an empty array if no such listeners have been added - Throws:
-
ClassCastException
- iflistenerType
doesn't specify a class or interface that implementsjava.util.EventListener
- Since:
- 1.3
- See Also:
-
Component.getComponentListeners()
,Component.getFocusListeners()
,Component.getHierarchyListeners()
,Component.getHierarchyBoundsListeners()
,Component.getKeyListeners()
,Component.getMouseListeners()
,Component.getMouseMotionListeners()
,Component.getMouseWheelListeners()
,Component.getInputMethodListeners()
,Component.getPropertyChangeListeners()
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.
Note that if the event parameter is null
the behavior is unspecified and may result in an exception.
- Overrides:
-
processEvent
in classComponent
- 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 viaaddAdjustmentListener
. - Adjustment events are enabled via
enableEvents
.
Note that if the event parameter is null
the behavior is unspecified and may result in an exception.
- 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 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
.
- Overrides:
-
paramString
in classComponent
- 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 interfaceAccessible
- Overrides:
-
getAccessibleContext
in classComponent
- Returns:
- an
AccessibleAWTScrollBar
that serves as theAccessibleContext
of thisScrollBar
- Since:
- 1.3
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