IT. Expert System.

Java Standard Edition (SE)

Scrollbar


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:
    JDK1.0
    See Also:
    AdjustmentEvent, AdjustmentListener, Serialized Form
    • Field Detail

      • 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 Detail

      • 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 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 Detail

      • 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:
        JDK1.1
        See Also:
        getOrientation()
      • 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:
        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 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:
        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 interface Adjustable
        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 interface Adjustable
        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 interface Adjustable
        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 interface Adjustable
        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 interface Adjustable
        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 interface Adjustable
        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()
      • 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:
        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 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 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


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