java.awt.Component
java.awt.Scrollbar
is new.
java.lang.Object
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
or
"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.
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 amount.
visible.
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:
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
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.
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 Class Summary | |
|---|---|
| protected class |
Scrollbar.AccessibleAWTScrollBar
This class implements accessibility support for the Scrollbar class. |
| Nested classes inherited from class java.awt. Component |
|---|
| Component.AccessibleAWTComponent , Component.BltBufferStrategy , Component.FlipBufferStrategy |
| 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. Adjustable |
|---|
| NO_ORIENTATION |
| 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, visible amount, 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. |
| AdjustmentListener [] |
getAdjustmentListeners
() Returns an array of all the adjustment listeners registered on 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) Returns an array of all the objects currently registered as FooListeners upon this Scrollbar. |
| int |
getMaximum
() Gets the maximum value of this scroll bar. |
| int |
getMinimum
() Gets the minimum value of this scroll bar. |
| int |
getOrientation
() Returns 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. |
| boolean |
getValueIsAdjusting
() Returns true if the value is in the process of changing as a result of actions being taken by the user. |
| 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 a string representing the state of this Scrollbar. |
| 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 |
setValueIsAdjusting
(boolean b) Sets the valueIsAdjusting property. |
| 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. |
| void |
setVisibleAmount
(int newAmount) Sets the visible amount of this scroll bar. |
| Methods inherited from class java.lang. Object |
|---|
| clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
| Field Detail |
|---|
public static final int HORIZONTAL
public static final int VERTICAL
| Constructor Detail |
|---|
public Scrollbar()
throws HeadlessException
| Property | Description | Default Value |
|---|---|---|
| orientation |
indicates
whether
or horizontal |
Scrollbar.VERTICAL |
| value |
value which controls the location of the scroll
bar's
|
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 |
public Scrollbar(int orientation)
throws HeadlessException
The orientation argument must take one of the two values Scrollbar.HORIZONTAL, or Scrollbar.VERTICAL, indicating a horizontal or vertical scroll bar, respectively.
public Scrollbar(int orientation,
int value,
int visible,
int minimum,
int maximum)
throws HeadlessException
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) .
visible - the visible amount of the scroll bar, typically represented by the size of the bubble
| Method Detail |
|---|
public void addNotify()
public int getOrientation()
public void setOrientation(int orientation)
public int getValue()
public void setValue(int newValue)
If the value supplied is less than the current minimum or greater than the current maximum - visibleAmount, then
either minimum or maximum - visibleAmount
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.
Calling this method does not fire an AdjustmentEvent.
public int getMinimum()
public void setMinimum(int newMinimum)
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.
When setMinimum is called, the limiting argument takes precedence over the existing scrollbar value.
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
Integer.MIN_VALUE
will result in the new minimum value
being
to be
set to
Integer.MAX_VALUE
Integer.MIN_VALUE
- 1.
public int getMaximum()
public void setMaximum(int newMaximum)
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.
When setMaximum is called, the limiting argument takes precedence over the existing scrollbar value.
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.
public int getVisibleAmount()
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 visible amount of a scroll bar is the range of values represented by the width of the scroll bar's 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.
public int getVisible()
public void setVisibleAmount(int newAmount)
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.
The visible amount of a scroll bar is the range of values represented by the width of the scroll bar's bubble.
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.
new
amount
public void setUnitIncrement(int v)
The unit increment is the value that is added
or subtracted
(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.
public void setLineIncrement(int v)
public int getUnitIncrement()
The unit increment is the value that is added
or subtracted
(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.
public int getLineIncrement()
public void setBlockIncrement(int v)
The block increment is the value that is added
or subtracted
(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.
public void setPageIncrement(int v)
public int getBlockIncrement()
The block increment is the value that is added
or subtracted
(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.
public int getPageIncrement()
public void setValues(int value,
int visible,
int minimum,
int maximum)
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.
positive,
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.
amount of the scroll bar
public boolean getValueIsAdjusting()
public void setValueIsAdjusting(boolean b)
public void addAdjustmentListener(AdjustmentListener l)
public void removeAdjustmentListener(AdjustmentListener l)
public AdjustmentListener[] getAdjustmentListeners()
public EventListener[] getListeners(Class listenerType)
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.
protected void processEvent(AWTEvent e)
Note that if the event parameter is null the behavior is unspecified and may result in an exception.
protected void processAdjustmentEvent(AdjustmentEvent e)
This method is not called unless adjustment events are enabled for this component. Adjustment events are enabled when one of the following occurs:
Note that if the event parameter is null the behavior is unspecified and may result in an exception.
protected String paramString()
public AccessibleContext getAccessibleContext()