Scrollbar (Java 2 Platform SE 5.0) (original) (raw)

java.awt

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 themaximum 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 implementAdjustmentListener, an interface defined in the package java.awt.event. Listeners can be added and removed dynamically by calling the methods addAdjustmentListener andremoveAdjustmentListener.

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

HORIZONTAL

public static final int HORIZONTAL

A constant that indicates a horizontal scroll bar.

See Also:

Constant Field Values

VERTICAL

public static final int VERTICAL

A constant that indicates a vertical scroll bar.

See Also:

Constant Field Values

Scrollbar

public Scrollbar() throws HeadlessException

Constructs a new vertical scroll bar. The default properties of the scroll bar are listed in the following table:

Throws:

[HeadlessException](../../java/awt/HeadlessException.html "class in java.awt") - 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](../../java/lang/IllegalArgumentException.html "class in java.lang") - when an illegal value for the orientation argument is supplied

[HeadlessException](../../java/awt/HeadlessException.html "class in java.awt") - 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)](../../java/awt/Scrollbar.html#setValues%28int, int, int, int%29).

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](../../java/lang/IllegalArgumentException.html "class in java.lang") - when an illegal value for the orientation argument is supplied

[HeadlessException](../../java/awt/HeadlessException.html "class in java.awt") - if GraphicsEnvironment.isHeadless() returns true.

See Also:

[setValues(int, int, int, int)](../../java/awt/Scrollbar.html#setValues%28int, int, int, int%29), GraphicsEnvironment.isHeadless()

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](../../java/awt/Component.html#addNotify%28%29) in class [Component](../../java/awt/Component.html "class in java.awt")

See Also:

Component.isDisplayable(), Component.removeNotify()

getOrientation

public int getOrientation()

Returns the orientation of this scroll bar.

Specified by:

[getOrientation](../../java/awt/Adjustable.html#getOrientation%28%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

Returns:

the orientation of this scroll bar, eitherScrollbar.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](../../java/lang/IllegalArgumentException.html "class in java.lang") - if the value supplied for orientation 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](../../java/awt/Adjustable.html#getValue%28%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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 anAdjustmentEvent.

Specified by:

[setValue](../../java/awt/Adjustable.html#setValue%28int%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

Parameters:

newValue - the new value of the scroll bar

See Also:

[setValues(int, int, int, int)](../../java/awt/Scrollbar.html#setValues%28int, int, int, int%29), getValue(), getMinimum(), getMaximum()

getMinimum

public int getMinimum()

Gets the minimum value of this scroll bar.

Specified by:

[getMinimum](../../java/awt/Adjustable.html#getMinimum%28%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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](../../java/awt/Adjustable.html#setMinimum%28int%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

Parameters:

newMinimum - the new minimum value for this scroll bar

Since:

JDK1.1

See Also:

[setValues(int, int, int, int)](../../java/awt/Scrollbar.html#setValues%28int, int, int, int%29), setMaximum(int)

getMaximum

public int getMaximum()

Gets the maximum value of this scroll bar.

Specified by:

[getMaximum](../../java/awt/Adjustable.html#getMaximum%28%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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](../../java/awt/Adjustable.html#setMaximum%28int%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

Parameters:

newMaximum - the new maximum value for this scroll bar

Since:

JDK1.1

See Also:

[setValues(int, int, int, int)](../../java/awt/Scrollbar.html#setValues%28int, int, int, int%29), 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.

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](../../java/awt/Adjustable.html#getVisibleAmount%28%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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.

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](../../java/awt/Adjustable.html#setVisibleAmount%28int%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

Parameters:

newAmount - the new visible amount

Since:

JDK1.1

See Also:

getVisibleAmount(), [setValues(int, int, int, int)](../../java/awt/Scrollbar.html#setValues%28int, int, int, int%29)

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.

Specified by:

[setUnitIncrement](../../java/awt/Adjustable.html#setUnitIncrement%28int%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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.

Specified by:

[getUnitIncrement](../../java/awt/Adjustable.html#getUnitIncrement%28%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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](../../java/awt/Adjustable.html#setBlockIncrement%28int%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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](../../java/awt/Adjustable.html#getBlockIncrement%28%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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 anAdjustmentEvent.

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 ofAdjustmentEvent from this scroll bar. If l is null, no exception is thrown and no action is performed.

Specified by:

[addAdjustmentListener](../../java/awt/Adjustable.html#addAdjustmentListener%28java.awt.event.AdjustmentListener%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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.

Specified by:

[removeAdjustmentListener](../../java/awt/Adjustable.html#removeAdjustmentListener%28java.awt.event.AdjustmentListener%29) in interface [Adjustable](../../java/awt/Adjustable.html "interface in java.awt")

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 AdjustmentListeners 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 listenerType)

Returns an array of all the objects currently registered as _Foo_Listeners upon this Scrollbar._Foo_Listeners are registered using theadd_Foo_Listener method.

You can specify the listenerType argument with a class literal, such as_Foo_Listener.class. For example, you can query aScrollbar 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](../../java/awt/Component.html#getListeners%28java.lang.Class%29) in class [Component](../../java/awt/Component.html "class in java.awt")

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_Foo_Listeners on this component, or an empty array if no such listeners have been added

Throws:

[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang") - if listenerType 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 theprocessAdjustmentEvent method. Otherwise, it invokes its superclass'sprocessEvent method.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

Overrides:

[processEvent](../../java/awt/Component.html#processEvent%28java.awt.AWTEvent%29) in class [Component](../../java/awt/Component.html "class in java.awt")

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 registeredAdjustmentListener 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.

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](../../java/awt/Component.html#paramString%28%29) in class [Component](../../java/awt/Component.html "class in java.awt")

Returns:

the parameter string of this scroll bar

getAccessibleContext

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this Scrollbar. For scrollbars, theAccessibleContext takes the form of an AccessibleAWTScrollBar. A newAccessibleAWTScrollBar instance is created if necessary.

Specified by:

[getAccessibleContext](../../javax/accessibility/Accessible.html#getAccessibleContext%28%29) in interface [Accessible](../../javax/accessibility/Accessible.html "interface in javax.accessibility")

Overrides:

[getAccessibleContext](../../java/awt/Component.html#getAccessibleContext%28%29) in class [Component](../../java/awt/Component.html "class in java.awt")

Returns:

an AccessibleAWTScrollBar that serves as the AccessibleContext of this ScrollBar

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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