javax.swing

Class JLayer<V extends Component>

java.lang.Object

java.awt.Component

java.awt.Container

javax.swing.JComponent

javax.swing.JLayer<V>

Type Parameters:

V - the type of JLayer's view component

All Implemented Interfaces:

ImageObserver, MenuContainer, PropertyChangeListener, Serializable, EventListener, Accessible, Scrollable

public final class JLayer<V extends Component>
extends JComponent
implements Scrollable, PropertyChangeListener, Accessible

JLayer is a universal decorator for Swing components which enables you to implement various advanced painting effects as well as receive notifications of all AWTEvents generated within its borders.

JLayer delegates the handling of painting and input events to a LayerUI object, which performs the actual decoration.

The custom painting implemented in the LayerUI and events notification work for the JLayer itself and all its subcomponents. This combination enables you to enrich existing components by adding new advanced functionality such as temporary locking of a hierarchy, data tips for compound components, enhanced mouse scrolling etc and so on.

JLayer is a good solution if you only need to do custom painting over compound component or catch input events from its subcomponents.

 import javax.swing.*;
 import javax.swing.plaf.LayerUI;
 import java.awt.*;

 public class JLayerSample {

     private static JLayer<JComponent> createLayer() {
         // This custom layerUI will fill the layer with translucent green
         // and print out all mouseMotion events generated within its borders
         LayerUI<JComponent> layerUI = new LayerUI<JComponent>() {

             public void paint(Graphics g, JComponent c) {
                 // paint the layer as is
                 super.paint(g, c);
                 // fill it with the translucent green
                 g.setColor(new Color(0, 128, 0, 128));
                 g.fillRect(0, 0, c.getWidth(), c.getHeight());
             }

             public void installUI(JComponent c) {
                 super.installUI(c);
                 // enable mouse motion events for the layer's subcomponents
                 ((JLayer) c).setLayerEventMask(AWTEvent.MOUSE_MOTION_EVENT_MASK);
             }

             public void uninstallUI(JComponent c) {
                 super.uninstallUI(c);
                 // reset the layer event mask
                 ((JLayer) c).setLayerEventMask(0);
             }

             // overridden method which catches MouseMotion events
             public void eventDispatched(AWTEvent e, JLayer<? extends JComponent> l) {
                 System.out.println("AWTEvent detected: " + e);
             }
         };
         // create a component to be decorated with the layer
         JPanel panel = new JPanel();
         panel.add(new JButton("JButton"));

         // create the layer for the panel using our custom layerUI
         return new JLayer<JComponent>(panel, layerUI);
     }

     private static void createAndShowGUI() {
         final JFrame frame = new JFrame();
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

         // work with the layer as with any other Swing component
         frame.add(createLayer());

         frame.setSize(200, 200);
         frame.setLocationRelativeTo(null);
         frame.setVisible(true);
     }

     public static void main(String[] args) throws Exception {
         SwingUtilities.invokeAndWait(new Runnable() {
             public void run() {
                 createAndShowGUI();
             }
         });
     }
 }
 

Note: JLayer doesn't support the following methods:

• Container.add(java.awt.Component)
• Container.add(String, java.awt.Component)
• Container.add(java.awt.Component, int)
• Container.add(java.awt.Component, Object)
• Container.add(java.awt.Component, Object, int)

using any of of them will cause UnsupportedOperationException to be thrown, to add a component to JLayer use setView(Component) or setGlassPane(JPanel).

Since:

1.7

See Also:

JLayer(Component), setView(Component), getView(), LayerUI, JLayer(Component, LayerUI), setUI(javax.swing.plaf.LayerUI), getUI()

Nested Class Summary

Nested classes/interfaces inherited from class javax.swing.JComponent

JComponent.AccessibleJComponent

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

Field Summary

Fields inherited from class javax.swing.JComponent

accessibleContext, listenerList, TOOL_TIP_TEXT_KEY, ui, UNDEFINED_CONDITION, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, WHEN_FOCUSED, WHEN_IN_FOCUSED_WINDOW

Fields inherited from class java.awt.Component

BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

Fields inherited from interface java.awt.image.ImageObserver

ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH

Constructor Summary

Constructors

Constructor and Description
JLayer() Creates a new JLayer object with a null view component and default LayerUI.
JLayer(V view) Creates a new JLayer object with default LayerUI.
JLayer(V view, LayerUI<V> ui) Creates a new JLayer object with the specified view component and LayerUI object.

Method Summary

Methods

Modifier and Type	Method and Description
protected void	addImpl(Component comp, Object constraints, int index) This method is not supported by JLayer and always throws UnsupportedOperationException
void	addNotify() Notifies this component that it now has a parent component.
JPanel	createGlassPane() Called by the constructor methods to create a default glassPane.
void	doLayout() Delegates its functionality to the LayerUI.doLayout(JLayer) method, if LayerUI is set.
AccessibleContext	getAccessibleContext() Gets the AccessibleContext associated with this JLayer.
JPanel	getGlassPane() Returns the JLayer's glassPane component or null.
long	getLayerEventMask() Returns the bitmap of event mask to receive by this JLayer and its LayerUI.
Dimension	getPreferredScrollableViewportSize() Returns the preferred size of the viewport for a view component.
int	getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) Returns a scroll increment, which is required for components that display logical rows or columns in order to completely expose one block of rows or columns, depending on the value of orientation.
boolean	getScrollableTracksViewportHeight() Returns false to indicate that the height of the viewport does not determine the height of the layer, unless the preferred height of the layer is smaller than the height of the viewport.
boolean	getScrollableTracksViewportWidth() Returns false to indicate that the width of the viewport does not determine the width of the layer, unless the preferred width of the layer is smaller than the width of the viewport.
int	getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) Returns a scroll increment, which is required for components that display logical rows or columns in order to completely expose one new row or column, depending on the value of orientation.
LayerUI<? super V>	getUI() Returns the LayerUI for this JLayer.
V	getView() Returns the JLayer's view component or null.
boolean	isOptimizedDrawingEnabled() The JLayer overrides the default implementation of this method (in JComponent) to return false.
protected boolean	isPaintingOrigin() Always returns true to cause painting to originate from JLayer, or one of its ancestors.
void	paint(Graphics g) Delegates all painting to the LayerUI object.
protected void	paintComponent(Graphics g) This method is empty, because all painting is done by paint(Graphics) and ComponentUI.update(Graphics, JComponent) methods
void	paintImmediately(int x, int y, int w, int h) Delegates its functionality to the LayerUI.paintImmediately(int, int, int, int, JLayer) method, if LayerUI is set.
void	propertyChange(PropertyChangeEvent evt) This method gets called when a bound property is changed.
void	remove(Component comp) Removes the specified component from this container.
void	removeAll() Removes all the components from this container.
void	removeNotify() Notifies this component that it no longer has a parent component.
void	setBorder(Border border) A non-null border, or non-zero insets, isn't supported, to prevent the geometry of this component from becoming complex enough to inhibit subclassing of LayerUI class.
void	setGlassPane(JPanel glassPane) Sets the JLayer's glassPane component, which can be null.
void	setLayerEventMask(long layerEventMask) Enables the events from JLayer and all its descendants defined by the specified event mask parameter to be delivered to the LayerUI.eventDispatched(AWTEvent, JLayer) method.
void	setLayout(LayoutManager mgr) Sets the layout manager for this container.
void	setUI(LayerUI<? super V> ui) Sets the LayerUI which will perform painting and receive input events for this JLayer.
void	setView(V view) Sets the JLayer's view component, which can be null.
void	updateUI() Delegates its functionality to the LayerUI.updateUI(JLayer) method, if LayerUI is set.

Methods inherited from class javax.swing.JComponent

addAncestorListener, addVetoableChangeListener, computeVisibleRect, contains, createToolTip, disable, enable, firePropertyChange, firePropertyChange, firePropertyChange, fireVetoableChange, getActionForKeyStroke, getActionMap, getAlignmentX, getAlignmentY, getAncestorListeners, getAutoscrolls, getBaseline, getBaselineResizeBehavior, getBorder, getBounds, getClientProperty, getComponentGraphics, getComponentPopupMenu, getConditionForKeyStroke, getDebugGraphicsOptions, getDefaultLocale, getFontMetrics, getGraphics, getHeight, getInheritsPopupMenu, getInputMap, getInputMap, getInputVerifier, getInsets, getInsets, getListeners, getLocation, getMaximumSize, getMinimumSize, getNextFocusableComponent, getPopupLocation, getPreferredSize, getRegisteredKeyStrokes, getRootPane, getSize, getToolTipLocation, getToolTipText, getToolTipText, getTopLevelAncestor, getTransferHandler, getUIClassID, getVerifyInputWhenFocusTarget, getVetoableChangeListeners, getVisibleRect, getWidth, getX, getY, grabFocus, isDoubleBuffered, isLightweightComponent, isManagingFocus, isOpaque, isPaintingForPrint, isPaintingTile, isRequestFocusEnabled, isValidateRoot, paintBorder, paintChildren, paintImmediately, paramString, print, printAll, printBorder, printChildren, printComponent, processComponentKeyEvent, processKeyBinding, processKeyEvent, processMouseEvent, processMouseMotionEvent, putClientProperty, registerKeyboardAction, registerKeyboardAction, removeAncestorListener, removeVetoableChangeListener, repaint, repaint, requestDefaultFocus, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, resetKeyboardActions, reshape, revalidate, scrollRectToVisible, setActionMap, setAlignmentX, setAlignmentY, setAutoscrolls, setBackground, setComponentPopupMenu, setDebugGraphicsOptions, setDefaultLocale, setDoubleBuffered, setEnabled, setFocusTraversalKeys, setFont, setForeground, setInheritsPopupMenu, setInputMap, setInputVerifier, setMaximumSize, setMinimumSize, setNextFocusableComponent, setOpaque, setPreferredSize, setRequestFocusEnabled, setToolTipText, setTransferHandler, setUI, setVerifyInputWhenFocusTarget, setVisible, unregisterKeyboardAction, update

Methods inherited from class java.awt.Container

add, add, add, add, add, addContainerListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, countComponents, deliverEvent, findComponentAt, findComponentAt, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents, getComponentZOrder, getContainerListeners, getFocusTraversalKeys, getFocusTraversalPolicy, getLayout, getMousePosition, insets, invalidate, isAncestorOf, isFocusCycleRoot, isFocusCycleRoot, isFocusTraversalPolicyProvider, isFocusTraversalPolicySet, layout, list, list, locate, minimumSize, paintComponents, preferredSize, printComponents, processContainerEvent, processEvent, remove, removeContainerListener, setComponentZOrder, setFocusCycleRoot, setFocusTraversalPolicy, setFocusTraversalPolicyProvider, transferFocusDownCycle, validate, validateTree

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, bounds, checkImage, checkImage, coalesceEvents, contains, createImage, createImage, createVolatileImage, createVolatileImage, disableEvents, dispatchEvent, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getBackground, getBounds, getColorModel, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeysEnabled, getFont, getForeground, getGraphicsConfiguration, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocationOnScreen, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPeer, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getToolkit, getTreeLock, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, isBackgroundSet, isCursorSet, isDisplayable, isEnabled, isFocusable, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, resize, resize, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setFocusable, setFocusTraversalKeysEnabled, setIgnoreRepaint, setLocale, setLocation, setLocation, setName, setSize, setSize, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

JLayer

public JLayer()

Creates a new JLayer object with a null view component and default LayerUI.

See Also:

setView(V), setUI(javax.swing.plaf.LayerUI<? super V>)

JLayer

public JLayer(V view)

Creates a new JLayer object with default LayerUI.

Parameters:

view - the component to be decorated by this JLayer

See Also:

setUI(javax.swing.plaf.LayerUI<? super V>)

JLayer

public JLayer(V view,
      LayerUI<V> ui)

Creates a new JLayer object with the specified view component and LayerUI object.

Parameters:

view - the component to be decorated

ui - the LayerUI delegate to be used by this JLayer

Method Detail

getView

public V getView()

Returns the JLayer's view component or null.
This is a bound property.

Returns:

the JLayer's view component or null if none exists

See Also:

setView(Component)

setView

public void setView(V view)

Sets the JLayer's view component, which can be null.
This is a bound property.

Parameters:

view - the view component for this JLayer

See Also:

getView()

setUI

public void setUI(LayerUI<? super V> ui)

Sets the LayerUI which will perform painting and receive input events for this JLayer.

Parameters:

ui - the LayerUI for this JLayer

getUI

public LayerUI<? super V> getUI()

Returns the LayerUI for this JLayer.

Returns:

the LayerUI for this JLayer

getGlassPane

public JPanel getGlassPane()

Returns the JLayer's glassPane component or null.
This is a bound property.

Returns:

the JLayer's glassPane component or null if none exists

See Also:

setGlassPane(JPanel)

setGlassPane

public void setGlassPane(JPanel glassPane)

Sets the JLayer's glassPane component, which can be null.
This is a bound property.

Parameters:

glassPane - the glassPane component of this JLayer

See Also:

getGlassPane()

createGlassPane

public JPanel createGlassPane()

Called by the constructor methods to create a default glassPane. By default this method creates a new JPanel with visibility set to true and opacity set to false.

Returns:

the default glassPane

setLayout

public void setLayout(LayoutManager mgr)

Sets the layout manager for this container. This method is overridden to prevent the layout manager from being set.

Note: If mgr is non-null, this method will throw an exception as layout managers are not supported on a JLayer.

Overrides:

setLayout in class Container

Parameters:

mgr - the specified layout manager

Throws:

IllegalArgumentException - this method is not supported

See Also:

Container.doLayout(), Container.getLayout(), Container.invalidate()

setBorder

public void setBorder(Border border)

A non-null border, or non-zero insets, isn't supported, to prevent the geometry of this component from becoming complex enough to inhibit subclassing of LayerUI class. To create a JLayer with a border, add it to a JPanel that has a border.

Note: If border is non-null, this method will throw an exception as borders are not supported on a JLayer.

Overrides:

setBorder in class JComponent

Parameters:

border - the Border to set

Throws:

IllegalArgumentException - this method is not supported

See Also:

Border, CompoundBorder

addImpl

protected void addImpl(Component comp,
           Object constraints,
           int index)

This method is not supported by JLayer and always throws UnsupportedOperationException

Overrides:

addImpl in class Container

Parameters:

comp - the component to be added

constraints - an object expressing layout constraints for this component

index - the position in the container's list at which to insert the component, where -1 means append to the end

Throws:

UnsupportedOperationException - this method is not supported

See Also:

setView(Component), setGlassPane(JPanel)

remove

public void remove(Component comp)

Removes the specified component from this container. This method also notifies the layout manager to remove the component from this container's layout via the removeLayoutComponent method.

This method changes layout-related information, and therefore, invalidates the component hierarchy. If the container has already been displayed, the hierarchy must be validated thereafter in order to reflect the changes.

Overrides:

remove in class Container

Parameters:

comp - the component to be removed

See Also:

Container.add(java.awt.Component), Container.invalidate(), Container.validate(), Container.remove(int)

removeAll

public void removeAll()

Removes all the components from this container. This method also notifies the layout manager to remove the components from this container's layout via the removeLayoutComponent method.

This method changes layout-related information, and therefore, invalidates the component hierarchy. If the container has already been displayed, the hierarchy must be validated thereafter in order to reflect the changes.

Overrides:

removeAll in class Container

See Also:

Container.add(java.awt.Component), Container.remove(int), Container.invalidate()

isPaintingOrigin

protected boolean isPaintingOrigin()

Always returns true to cause painting to originate from JLayer, or one of its ancestors.

Overrides:

isPaintingOrigin in class JComponent

Returns:

true

See Also:

JComponent.isPaintingOrigin()

paintImmediately

public void paintImmediately(int x,
                    int y,
                    int w,
                    int h)

Delegates its functionality to the LayerUI.paintImmediately(int, int, int, int, JLayer) method, if LayerUI is set.

Overrides:

paintImmediately in class JComponent

Parameters:

x - the x value of the region to be painted

y - the y value of the region to be painted

w - the width of the region to be painted

h - the height of the region to be painted

See Also:

JComponent.repaint(long, int, int, int, int), JComponent.isPaintingOrigin()

paint

public void paint(Graphics g)

Delegates all painting to the LayerUI object.

Overrides:

paint in class JComponent

Parameters:

g - the Graphics to render to

See Also:

JComponent.paintComponent(java.awt.Graphics), JComponent.paintBorder(java.awt.Graphics), JComponent.paintChildren(java.awt.Graphics), JComponent.getComponentGraphics(java.awt.Graphics), JComponent.repaint(long, int, int, int, int)

paintComponent

protected void paintComponent(Graphics g)

This method is empty, because all painting is done by paint(Graphics) and ComponentUI.update(Graphics, JComponent) methods

Overrides:

paintComponent in class JComponent

Parameters:

g - the Graphics object to protect

See Also:

JComponent.paint(java.awt.Graphics), ComponentUI

isOptimizedDrawingEnabled

public boolean isOptimizedDrawingEnabled()

The JLayer overrides the default implementation of this method (in JComponent) to return false. This ensures that the drawing machinery will call the JLayer's paint implementation rather than messaging the JLayer's children directly.

Overrides:

isOptimizedDrawingEnabled in class JComponent

Returns:

false

propertyChange

public void propertyChange(PropertyChangeEvent evt)

This method gets called when a bound property is changed.

Specified by:

propertyChange in interface PropertyChangeListener

Parameters:

evt - A PropertyChangeEvent object describing the event source and the property that has changed.

setLayerEventMask

public void setLayerEventMask(long layerEventMask)

Enables the events from JLayer and all its descendants defined by the specified event mask parameter to be delivered to the LayerUI.eventDispatched(AWTEvent, JLayer) method.

Events are delivered provided that LayerUI is set for this JLayer and the JLayer is displayable.

The following example shows how to correctly use this method in the LayerUI implementations:

    public void installUI(JComponent c) {
       super.installUI(c);
       JLayer l = (JLayer) c;
       // this LayerUI will receive only key and focus events
       l.setLayerEventMask(AWTEvent.KEY_EVENT_MASK | AWTEvent.FOCUS_EVENT_MASK);
    }

    public void uninstallUI(JComponent c) {
       super.uninstallUI(c);
       JLayer l = (JLayer) c;
       // JLayer must be returned to its initial state
       l.setLayerEventMask(0);
    }
 

By default JLayer receives no events and its event mask is 0.

Parameters:

layerEventMask - the bitmask of event types to receive

See Also:

getLayerEventMask(), LayerUI.eventDispatched(AWTEvent, JLayer), Component.isDisplayable()

getLayerEventMask

public long getLayerEventMask()

Returns the bitmap of event mask to receive by this JLayer and its LayerUI.

It means that LayerUI.eventDispatched(AWTEvent, JLayer) method will only receive events that match the event mask.

By default JLayer receives no events.

Returns:

the bitmask of event types to receive for this JLayer

updateUI

public void updateUI()

Delegates its functionality to the LayerUI.updateUI(JLayer) method, if LayerUI is set.

Overrides:

updateUI in class JComponent

See Also:

JComponent.setUI(javax.swing.plaf.ComponentUI), UIManager.getLookAndFeel(), UIManager.getUI(javax.swing.JComponent)

getPreferredScrollableViewportSize

public Dimension getPreferredScrollableViewportSize()

Returns the preferred size of the viewport for a view component.

If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

Specified by:

getPreferredScrollableViewportSize in interface Scrollable

Returns:

the preferred size of the viewport for a view component

See Also:

Scrollable

getScrollableBlockIncrement

public int getScrollableBlockIncrement(Rectangle visibleRect,
                              int orientation,
                              int direction)

Returns a scroll increment, which is required for components that display logical rows or columns in order to completely expose one block of rows or columns, depending on the value of orientation.

If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

Specified by:

getScrollableBlockIncrement in interface Scrollable

Parameters:

visibleRect - The view area visible within the viewport

orientation - Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.

direction - Less than zero to scroll up/left, greater than zero for down/right.

Returns:

the "block" increment for scrolling in the specified direction

See Also:

Scrollable

getScrollableTracksViewportHeight

public boolean getScrollableTracksViewportHeight()

Returns false to indicate that the height of the viewport does not determine the height of the layer, unless the preferred height of the layer is smaller than the height of the viewport.

If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

Specified by:

getScrollableTracksViewportHeight in interface Scrollable

Returns:

whether the layer should track the height of the viewport

See Also:

Scrollable

getScrollableTracksViewportWidth

public boolean getScrollableTracksViewportWidth()

Returns false to indicate that the width of the viewport does not determine the width of the layer, unless the preferred width of the layer is smaller than the width of the viewport.

If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

Specified by:

getScrollableTracksViewportWidth in interface Scrollable

Returns:

whether the layer should track the width of the viewport

See Also:

Scrollable

getScrollableUnitIncrement

public int getScrollableUnitIncrement(Rectangle visibleRect,
                             int orientation,
                             int direction)

Returns a scroll increment, which is required for components that display logical rows or columns in order to completely expose one new row or column, depending on the value of orientation. Ideally, components should handle a partially exposed row or column by returning the distance required to completely expose the item.

Scrolling containers, like JScrollPane, will use this method each time the user requests a unit scroll.

If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

Specified by:

getScrollableUnitIncrement in interface Scrollable

Parameters:

visibleRect - The view area visible within the viewport

orientation - Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.

direction - Less than zero to scroll up/left, greater than zero for down/right.

Returns:

The "unit" increment for scrolling in the specified direction. This value should always be positive.

See Also:

Scrollable

addNotify

public void addNotify()

Notifies this component that it now has a parent component. When this method is invoked, the chain of parent components is set up with KeyboardAction event listeners. This method is called by the toolkit internally and should not be called directly by programs.

Overrides:

addNotify in class JComponent

See Also:

JComponent.registerKeyboardAction(java.awt.event.ActionListener, java.lang.String, javax.swing.KeyStroke, int)

removeNotify

public void removeNotify()

Notifies this component that it no longer has a parent component. When this method is invoked, any KeyboardActions set up in the the chain of parent components are removed. This method is called by the toolkit internally and should not be called directly by programs.

Overrides:

removeNotify in class JComponent

See Also:

JComponent.registerKeyboardAction(java.awt.event.ActionListener, java.lang.String, javax.swing.KeyStroke, int)

doLayout

public void doLayout()

Delegates its functionality to the LayerUI.doLayout(JLayer) method, if LayerUI is set.

Overrides:

doLayout in class Container

See Also:

LayoutManager.layoutContainer(java.awt.Container), Container.setLayout(java.awt.LayoutManager), Container.validate()

getAccessibleContext

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this JLayer.

Specified by:

getAccessibleContext in interface Accessible

Overrides:

getAccessibleContext in class JComponent

Returns:

the AccessibleContext associated with this JLayer.