ScrollPane
Class ScrollPane
- java.lang.Object
-
- java.awt.Component
-
- java.awt.Container
-
- java.awt.ScrollPane
- All Implemented Interfaces:
- ImageObserver, MenuContainer, Serializable, Accessible
public class ScrollPane extends Container implements Accessible
A container class which implements automatic horizontal and/or vertical scrolling for a single child component. The display policy for the scrollbars can be set to:
- as needed: scrollbars created and shown only when needed by scrollpane
- always: scrollbars created and always shown by the scrollpane
- never: scrollbars never created or shown by the scrollpane
The state of the horizontal and vertical scrollbars is represented by two ScrollPaneAdjustable
objects (one for each dimension) which implement the Adjustable
interface. The API provides methods to access those objects such that the attributes on the Adjustable object (such as unitIncrement, value, etc.) can be manipulated.
Certain adjustable properties (minimum, maximum, blockIncrement, and visibleAmount) are set internally by the scrollpane in accordance with the geometry of the scrollpane and its child and these should not be set by programs using the scrollpane.
If the scrollbar display policy is defined as "never", then the scrollpane can still be programmatically scrolled using the setScrollPosition() method and the scrollpane will move and clip the child's contents appropriately. This policy is useful if the program needs to create and manage its own adjustable controls.
The placement of the scrollbars is controlled by platform-specific properties set by the user outside of the program.
The initial size of this container is set to 100x100, but can be reset using setSize().
Scrolling with the wheel on a wheel-equipped mouse is enabled by default. This can be disabled using setWheelScrollingEnabled
. Wheel scrolling can be customized by setting the block and unit increment of the horizontal and vertical Adjustables. For information on how mouse wheel events are dispatched, see the class description for MouseWheelEvent
.
Insets are used to define any space used by scrollbars and any borders created by the scroll pane. getInsets() can be used to get the current value for the insets. If the value of scrollbarsAlwaysVisible is false, then the value of the insets will change dynamically depending on whether the scrollbars are currently visible or not.
Nested Classes
Modifier and Type | Class and Description |
---|---|
protected class |
ScrollPane.AccessibleAWTScrollPane This class implements accessibility support for the |
Nested classes/interfaces inherited from class java.awt.Container
Container.AccessibleAWTContainer
Nested classes/interfaces inherited from class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy
Fields
SCROLLBARS_AS_NEEDED
public static final int SCROLLBARS_AS_NEEDED
Specifies that horizontal/vertical scrollbar should be shown only when the size of the child exceeds the size of the scrollpane in the horizontal/vertical dimension.
SCROLLBARS_ALWAYS
public static final int SCROLLBARS_ALWAYS
Specifies that horizontal/vertical scrollbars should always be shown regardless of the respective sizes of the scrollpane and child.
SCROLLBARS_NEVER
public static final int SCROLLBARS_NEVER
Specifies that horizontal/vertical scrollbars should never be shown regardless of the respective sizes of the scrollpane and child.
Constructors
ScrollPane
public ScrollPane() throws HeadlessException
Create a new scrollpane container with a scrollbar display policy of "as needed".
- Throws:
-
HeadlessException
- if GraphicsEnvironment.isHeadless() returns true - See Also:
GraphicsEnvironment.isHeadless()
ScrollPane
@ConstructorProperties(value="scrollbarDisplayPolicy") public ScrollPane(int scrollbarDisplayPolicy) throws HeadlessException
Create a new scrollpane container.
- Parameters:
-
scrollbarDisplayPolicy
- policy for when scrollbars should be shown - Throws:
-
IllegalArgumentException
- if the specified scrollbar display policy is invalid -
HeadlessException
- if GraphicsEnvironment.isHeadless() returns true - See Also:
GraphicsEnvironment.isHeadless()
Methods
addImpl
protected final void addImpl(Component comp, Object constraints, int index)
Adds the specified component to this scroll pane container. If the scroll pane has an existing child component, that component is removed and the new one is added.
- Overrides:
-
addImpl
in classContainer
- Parameters:
-
comp
- the component to be added -
constraints
- not applicable -
index
- position of child component (must be <= 0) - See Also:
-
Container.add(Component)
,Container.add(Component, int)
,Container.add(Component, java.lang.Object)
,Container.invalidate()
,LayoutManager
,LayoutManager2
getScrollbarDisplayPolicy
public int getScrollbarDisplayPolicy()
Returns the display policy for the scrollbars.
- Returns:
- the display policy for the scrollbars
getViewportSize
public Dimension getViewportSize()
Returns the current size of the scroll pane's view port.
- Returns:
- the size of the view port in pixels
getHScrollbarHeight
public int getHScrollbarHeight()
Returns the height that would be occupied by a horizontal scrollbar, which is independent of whether it is currently displayed by the scroll pane or not.
- Returns:
- the height of a horizontal scrollbar in pixels
getVScrollbarWidth
public int getVScrollbarWidth()
Returns the width that would be occupied by a vertical scrollbar, which is independent of whether it is currently displayed by the scroll pane or not.
- Returns:
- the width of a vertical scrollbar in pixels
getVAdjustable
public Adjustable getVAdjustable()
Returns the ScrollPaneAdjustable
object which represents the state of the vertical scrollbar. The declared return type of this method is Adjustable
to maintain backward compatibility.
- See Also:
ScrollPaneAdjustable
getHAdjustable
public Adjustable getHAdjustable()
Returns the ScrollPaneAdjustable
object which represents the state of the horizontal scrollbar. The declared return type of this method is Adjustable
to maintain backward compatibility.
- See Also:
ScrollPaneAdjustable
setScrollPosition
public void setScrollPosition(int x, int y)
Scrolls to the specified position within the child component. A call to this method is only valid if the scroll pane contains a child. Specifying a position outside of the legal scrolling bounds of the child will scroll to the closest legal position. Legal bounds are defined to be the rectangle: x = 0, y = 0, width = (child width - view port width), height = (child height - view port height). This is a convenience method which interfaces with the Adjustable objects which represent the state of the scrollbars.
- Parameters:
-
x
- the x position to scroll to -
y
- the y position to scroll to - Throws:
-
NullPointerException
- if the scrollpane does not contain a child
setScrollPosition
public void setScrollPosition(Point p)
Scrolls to the specified position within the child component. A call to this method is only valid if the scroll pane contains a child and the specified position is within legal scrolling bounds of the child. Specifying a position outside of the legal scrolling bounds of the child will scroll to the closest legal position. Legal bounds are defined to be the rectangle: x = 0, y = 0, width = (child width - view port width), height = (child height - view port height). This is a convenience method which interfaces with the Adjustable objects which represent the state of the scrollbars.
- Parameters:
-
p
- the Point representing the position to scroll to - Throws:
-
NullPointerException
- ifp
isnull
getScrollPosition
public Point getScrollPosition()
Returns the current x,y position within the child which is displayed at the 0,0 location of the scrolled panel's view port. This is a convenience method which interfaces with the adjustable objects which represent the state of the scrollbars.
- Returns:
- the coordinate position for the current scroll position
- Throws:
-
NullPointerException
- if the scrollpane does not contain a child
setLayout
public final void setLayout(LayoutManager mgr)
Sets the layout manager for this container. This method is overridden to prevent the layout mgr from being set.
- Overrides:
-
setLayout
in classContainer
- Parameters:
-
mgr
- the specified layout manager - See Also:
-
Container.doLayout()
,Container.getLayout()
,Container.invalidate()
doLayout
public void doLayout()
Lays out this container by resizing its child to its preferred size. If the new preferred size of the child causes the current scroll position to be invalid, the scroll position is set to the closest valid position.
- Overrides:
-
doLayout
in classContainer
- See Also:
Component.validate()
layout
@Deprecated public void layout()
Deprecated. As of JDK version 1.1, replaced by doLayout()
.
printComponents
public void printComponents(Graphics g)
Prints the component in this scroll pane.
- Overrides:
-
printComponents
in classContainer
- Parameters:
-
g
- the specified Graphics window - See Also:
-
Component.print(java.awt.Graphics)
,Component.printAll(java.awt.Graphics)
addNotify
public void addNotify()
Creates the scroll pane's peer.
- Overrides:
-
addNotify
in classContainer
- See Also:
-
Component.isDisplayable()
,Container.removeNotify()
paramString
public String paramString()
Returns a string representing the state of this ScrollPane
. 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 classContainer
- Returns:
- the parameter string of this scroll pane
processMouseWheelEvent
protected void processMouseWheelEvent(MouseWheelEvent e)
Process mouse wheel events that are delivered to this ScrollPane
by scrolling an appropriate amount.
Note that if the event parameter is null
the behavior is unspecified and may result in an exception.
- Overrides:
-
processMouseWheelEvent
in classComponent
- Parameters:
-
e
- the mouse wheel event - Since:
- 1.4
- See Also:
-
MouseWheelEvent
,MouseWheelListener
,Component.addMouseWheelListener(java.awt.event.MouseWheelListener)
,Component.enableEvents(long)
eventTypeEnabled
protected boolean eventTypeEnabled(int type)
If wheel scrolling is enabled, we return true for MouseWheelEvents
- Since:
- 1.4
setWheelScrollingEnabled
public void setWheelScrollingEnabled(boolean handleWheel)
Enables/disables scrolling in response to movement of the mouse wheel. Wheel scrolling is enabled by default.
- Parameters:
-
handleWheel
-true
if scrolling should be done automatically for a MouseWheelEvent,false
otherwise. - Since:
- 1.4
- See Also:
-
isWheelScrollingEnabled()
,MouseWheelEvent
,MouseWheelListener
isWheelScrollingEnabled
public boolean isWheelScrollingEnabled()
Indicates whether or not scrolling will take place in response to the mouse wheel. Wheel scrolling is enabled by default.
- Since:
- 1.4
- See Also:
setWheelScrollingEnabled(boolean)
getAccessibleContext
public AccessibleContext getAccessibleContext()
Gets the AccessibleContext associated with this ScrollPane. For scroll panes, the AccessibleContext takes the form of an AccessibleAWTScrollPane. A new AccessibleAWTScrollPane instance is created if necessary.
- Specified by:
-
getAccessibleContext
in interfaceAccessible
- Overrides:
-
getAccessibleContext
in classComponent
- Returns:
- an AccessibleAWTScrollPane that serves as the AccessibleContext of this ScrollPane
- Since:
- 1.3
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