Module java.desktop
Package java.awt

Class 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:

Image shows 3 vertical sliders,
 side-by-side.

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:

Image shows horizontal slider with starting range of 0 and ending range
 of 300. The slider thumb is labeled 60.

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.

Since:
1.0
See Also:
AdjustmentEvent, AdjustmentListener, Serialized Form
  • Field Details

    • 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
  • Constructor Details

    • Scrollbar

      public Scrollbar() throws HeadlessException
      Constructs a new vertical scroll bar. The default properties of the scroll bar are listed in the following table:
      Scrollbar default properties
      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 the orientation 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 the orientation argument is supplied
      HeadlessException - if GraphicsEnvironment.isHeadless() returns true.
      See Also:
      setValues(int, int, int, int), GraphicsEnvironment.isHeadless()
  • Method Details

    • 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 class Component
      See Also:
      Component.isDisplayable(), Component.removeNotify(), Component.invalidate()
    • getOrientation

      public int getOrientation()
      Returns the orientation of this scroll bar.
      Specified by:
      getOrientation in interface Adjustable
      Returns:
      the orientation of this scroll bar, either Scrollbar.HORIZONTAL or Scrollbar.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, either Scrollbar.HORIZONTAL or Scrollbar.VERTICAL
      Throws:
      IllegalArgumentException - if the value supplied for orientation is not a legal value
      Since:
      1.1
      See Also:
      getOrientation()
    • getValue

      public int getValue()
      Gets the current value of this scroll bar.
      Specified by:
      getValue in interface Adjustable
      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 interface Adjustable
      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 interface Adjustable
      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 interface Adjustable
      Parameters:
      newMinimum - the new minimum value for this scroll bar
      Since:
      1.1
      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 interface Adjustable
      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 interface Adjustable
      Parameters:
      newMaximum - the new maximum value for this scroll bar
      Since:
      1.1
      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 interface Adjustable
      Returns:
      the visible amount of this scroll bar
      Since:
      1.1
      See Also:
      setVisibleAmount(int)
    • getVisible

      @Deprecated public int getVisible()
      Deprecated.
      As of JDK version 1.1, replaced by getVisibleAmount().
      Returns the visible amount of this scroll bar.
      Returns:
      the visible amount of this scroll bar
    • 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 interface Adjustable
      Parameters:
      newAmount - the new visible amount
      Since:
      1.1
      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. Attempts 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 interface Adjustable
      Parameters:
      v - the amount by which to increment or decrement the scroll bar's value
      Since:
      1.1
      See Also:
      getUnitIncrement()
    • setLineIncrement

      @Deprecated public void setLineIncrement​(int v)
      Deprecated.
      As of JDK version 1.1, replaced by setUnitIncrement(int).
      Sets the unit increment for this scroll bar.
      Parameters:
      v - the increment value
    • 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 interface Adjustable
      Returns:
      the unit increment of this scroll bar
      Since:
      1.1
      See Also:
      setUnitIncrement(int)
    • getLineIncrement

      @Deprecated public int getLineIncrement()
      Deprecated.
      As of JDK version 1.1, replaced by getUnitIncrement().
      Returns the unit increment for this scrollbar.
      Returns:
      the unit increment for this scrollbar
    • 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. Attempts to set the block increment to a value lower than 1 will result in a value of 1 being set.

      Specified by:
      setBlockIncrement in interface Adjustable
      Parameters:
      v - the amount by which to increment or decrement the scroll bar's value
      Since:
      1.1
      See Also:
      getBlockIncrement()
    • setPageIncrement

      @Deprecated public void setPageIncrement​(int v)
      Deprecated.
      As of JDK version 1.1, replaced by setBlockIncrement().
      Sets the block increment for this scroll bar.
      Parameters:
      v - the block increment
    • 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 interface Adjustable
      Returns:
      the block increment of this scroll bar
      Since:
      1.1
      See Also:
      setBlockIncrement(int)
    • getPageIncrement

      @Deprecated public int getPageIncrement()
      Deprecated.
      As of JDK version 1.1, replaced by getBlockIncrement().
      Returns the block increment of this scroll bar.
      Returns:
      the block increment of this scroll bar
    • 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 interface Adjustable
      Parameters:
      l - the adjustment listener
      Since:
      1.1
      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 interface Adjustable
      Parameters:
      l - the adjustment listener
      Since:
      1.1
      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<T> listenerType)
      Returns an array of all the objects currently registered as FooListeners upon this Scrollbar. FooListeners 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 class Component
      Type Parameters:
      T - the type of the listeners
      Parameters:
      listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener
      Returns:
      an array of all objects registered as FooListeners on this component, or an empty array if no such listeners have been added
      Throws:
      ClassCastException - if listenerType doesn't specify a class or interface that implements java.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 class Component
      Parameters:
      e - the event
      Since:
      1.1
      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 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:
      1.1
      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 class Component
      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 interface Accessible
      Overrides:
      getAccessibleContext in class Component
      Returns:
      an AccessibleAWTScrollBar that serves as the AccessibleContext of this ScrollBar
      Since:
      1.3