Class ScrollPane

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:

1. as needed: scrollbars created and shown only when needed by scrollpane
2. always: scrollbars created and always shown by the scrollpane
3. 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.

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.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

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 class Container

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 - if p is null

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 class Container

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 class Container

See Also:

Component.validate()

layout

@Deprecated
public void layout()

Deprecated. As of JDK version 1.1, replaced by doLayout().

Overrides:

layout in class Container

printComponents

public void printComponents(Graphics g)

Prints the component in this scroll pane.

Overrides:

printComponents in class Container

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 class Container

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 class Container

Returns:

the parameter string of this scroll pane

processMouseWheelEvent

protected void processMouseWheelEvent(MouseWheelEvent e)

Overrides:

processMouseWheelEvent in class Component

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 interface Accessible

Overrides:

getAccessibleContext in class Component

Returns:

an AccessibleAWTScrollPane that serves as the AccessibleContext of this ScrollPane

Since:

1.3