java.awt
Class Scrollbar

java.lang.Object
  |
  +--java.awt.Component
        |
        +--java.awt.Scrollbar
All Implemented Interfaces:
Accessible, Adjustable, ImageObserver, MenuContainer, Serializable
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" 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 the platform is discouraged. The five types of adjustment event introduced with JDK 1.1 correspond to the five event types that are associated with scroll bars in previous platform versions. The following list gives the adjustment event type, and the corresponding JDK 1.0 event type it replaces.

  • 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

Since:
JDK1.0
See Also:
AdjustmentEvent, AdjustmentListener, Serialized Form

 

Nested Class Summary

protected  class Scrollbar.AccessibleAWTScrollBar
    This class implements accessibility support for the Scrollbar class.
 
Nested classes inherited from class java.awt.Component
Component.BltBufferStrategy, Component.FlipBufferStrategy
 

 

Field Summary

static int HORIZONTAL
    A constant that indicates a horizontal scroll bar.
static int VERTICAL
    A constant that indicates a vertical scroll bar.
 
Fields inherited from class java.awt.Component
BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT
 
Fields inherited from interface java.awt.Adjustable
NO_ORIENTATION
 
Fields inherited from interface java.awt.image.ImageObserver
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH
 

 

Constructor Summary

Scrollbar()
    Constructs a new vertical scroll bar.
Scrollbar(int orientation)
    Constructs a new scroll bar with the specified orientation.
Scrollbar(int orientation, int value, int visible, int minimum, int maximum)
    Constructs a new scroll bar with the specified orientation, initial value, visible amount, and minimum and maximum values.
 

 

Method Summary

 void addAdjustmentListener(AdjustmentListener l)
    Adds the specified adjustment listener to receive instances of AdjustmentEvent from this scroll bar.
 void addNotify()
    Creates the Scrollbar's peer.
 AccessibleContext getAccessibleContext()
    Gets the AccessibleContext associated with this Scrollbar.
 AdjustmentListener[] getAdjustmentListeners()
    Returns an array of all the adjustment listeners registered on this scrollbar.
 int getBlockIncrement()
    Gets the block increment of this scroll bar.
 int getLineIncrement()
    Deprecated. As of JDK version 1.1, replaced by getUnitIncrement().
 EventListener[] getListeners(Class listenerType)
    Returns an array of all the objects currently registered as FooListeners upon this Scrollbar.
 int getMaximum()
    Gets the maximum value of this scroll bar.
 int getMinimum()
    Gets the minimum value of this scroll bar.
 int getOrientation()
    Returns the orientation of this scroll bar.
 int getPageIncrement()
    Deprecated. As of JDK version 1.1, replaced by getBlockIncrement().
 int getUnitIncrement()
    Gets the unit increment for this scrollbar.
 int getValue()
    Gets the current value of this scroll bar.
 boolean getValueIsAdjusting()
    Returns true if the value is in the process of changing as a result of actions being taken by the user.
 int getVisible()
    Deprecated. As of JDK version 1.1, replaced by getVisibleAmount().
 int getVisibleAmount()
    Gets the visible amount of this scroll bar.
protected  String paramString()
    Returns a string representing the state of this Scrollbar.
protected  void processAdjustmentEvent(AdjustmentEvent e)
    Processes adjustment events occurring on this scrollbar by dispatching them to any registered AdjustmentListener objects.
protected  void processEvent(AWTEvent e)
    Processes events on this scroll bar.
 void removeAdjustmentListener(AdjustmentListener l)
    Removes the specified adjustment listener so that it no longer receives instances of AdjustmentEvent from this scroll bar.
 void setBlockIncrement(int v)
    Sets the block increment for this scroll bar.
 void setLineIncrement(int v)
    Deprecated. As of JDK version 1.1, replaced by setUnitIncrement(int).
 void setMaximum(int newMaximum)
    Sets the maximum value of this scroll bar.
 void setMinimum(int newMinimum)
    Sets the minimum value of this scroll bar.
 void setOrientation(int orientation)
    Sets the orientation for this scroll bar.
 void setPageIncrement(int v)
    Deprecated. As of JDK version 1.1, replaced by setBlockIncrement().
 void setUnitIncrement(int v)
    Sets the unit increment for this scroll bar.
 void setValue(int newValue)
    Sets the value of this scroll bar to the specified value.
 void setValueIsAdjusting(boolean b)
    Sets the valueIsAdjusting property.
 void setValues(int value, int visible, int minimum, int maximum)
    Sets the values of four properties for this scroll bar: value, visibleAmount, minimum, and maximum.
 void setVisibleAmount(int newAmount)
    Sets the visible amount of this scroll bar.
 
Methods inherited from class java.awt.Component
action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeys, getFocusTraversalKeysEnabled, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getMinimumSize, getMouseListeners, getMouseMotionListeners, getMouseWheelListeners, getName, getParent, getPeer, getPreferredSize, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, invalidate, isBackgroundSet, isCursorSet, isDisplayable, isDoubleBuffered, isEnabled, isFocusable, isFocusCycleRoot, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isOpaque, isShowing, isValid, isVisible, keyDown, keyUp, layout, list, list, list, list, list, locate, location, lostFocus, minimumSize, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paint, paintAll, postEvent, preferredSize, prepareImage, prepareImage, print, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, reshape,