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JavaTM 2 Platform Standard Edition |
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SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
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" 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:
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
AdjustmentEvent
,
AdjustmentListener
, Serialized FormField 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 |
HORIZONTAL,
VERTICAL |
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. |
int |
getBlockIncrement()
Gets the block increment of this scroll bar. |
int |
getLineIncrement()
Deprecated. As of JDK version 1.1, replaced by getUnitIncrement() . |
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.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()
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 |
public Scrollbar(int 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.orientation
argument is supplied.public Scrollbar(int orientation, int value, int visible, int minimum, int maximum)
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.
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 |
public void addNotify()
public int getOrientation()
Scrollbar.HORIZONTAL
or
Scrollbar.VERTICAL
.setOrientation(int)
public void setOrientation(int orientation)
the
- orientation of this scroll bar, either
Scrollbar.HORIZONTAL
or
Scrollbar.VERTICAL
.orientation
is not a
legal value.getOrientation()
public int getValue()
getMinimum()
,
getMaximum()
public void setValue(int newValue)
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.
newValue
- the new value of the scroll bar.setValues(int, int, int, int)
,
getValue()
,
getMinimum()
,
getMaximum()
public int getMinimum()
getValue()
,
getMaximum()
public void setMinimum(int newMinimum)
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.
newMinimum
- the new minimum value
for this scroll bar.setValues(int, int, int, int)
,
setMaximum(int)
public int getMaximum()
getValue()
,
getMinimum()
public void setMaximum(int newMaximum)
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.
newMaximum
- the new maximum value
for this scroll bar.java.awtScrollbar#setValues
,
java.awtScrollbar#setMinimum
public int getVisibleAmount()
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.
setVisibleAmount(int)
public int getVisible()
getVisibleAmount()
.
public void setVisibleAmount(int newAmount)
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.
newAmount
- the amount visible per page.getVisibleAmount()
,
setValues(int, int, int, int)
public void setUnitIncrement(int v)
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.
v
- the amount by which to increment or decrement
the scroll bar's value.getUnitIncrement()
public void setLineIncrement(int v)
setUnitIncrement(int)
.
public int getUnitIncrement()
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.
setUnitIncrement(int)
public int getLineIncrement()
getUnitIncrement()
.
public void setBlockIncrement(int v)
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.
v
- the amount by which to increment or decrement
the scroll bar's value.getBlockIncrement()
public void setPageIncrement(int v)
setBlockIncrement()
.
public int getBlockIncrement()
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.
setBlockIncrement(int)
public int getPageIncrement()
getBlockIncrement()
.
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 constraints that maximum cannot be less than minimum, and that value cannot be less than the minimum or greater than the maximum.
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.public void addAdjustmentListener(AdjustmentListener l)
AdjustmentEvent
from this scroll bar.
If l is null, no exception is thrown and no action is performed.l
- the adjustment listener.AdjustmentEvent
,
AdjustmentListener
,
removeAdjustmentListener(java.awt.event.AdjustmentListener)
public void removeAdjustmentListener(AdjustmentListener l)
AdjustmentEvent
from this scroll bar.
If l is null, no exception is thrown and no action is performed.l
- the adjustment listener.AdjustmentEvent
,
AdjustmentListener
,
addAdjustmentListener(java.awt.event.AdjustmentListener)
protected void processEvent(AWTEvent e)
AdjustmentEvent
, it invokes the
processAdjustmentEvent
method.
Otherwise, it invokes its superclass's
processEvent
method.e
- the event.AdjustmentEvent
,
processAdjustmentEvent(java.awt.event.AdjustmentEvent)
protected void processAdjustmentEvent(AdjustmentEvent e)
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
.
e
- the adjustment event.AdjustmentEvent
,
AdjustmentListener
,
addAdjustmentListener(java.awt.event.AdjustmentListener)
,
Component.enableEvents(long)
protected String paramString()
|
JavaTM 2 Platform Standard Edition |
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SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |