Class JLayeredPane

All Implemented Interfaces:
ImageObserver, MenuContainer, Serializable, Accessible
Direct Known Subclasses:
JDesktopPane

public class JLayeredPane
extends JComponent
implements Accessible

JLayeredPane adds depth to a JFC/Swing container, allowing components to overlap each other when needed. An Integer object specifies each component's depth in the container, where higher-numbered components sit "on top" of other components. For task-oriented documentation and examples of using layered panes see How to Use a Layered Pane, a section in The Java Tutorial.

The following text describes this image.

For convenience, JLayeredPane divides the depth-range into several different layers. Putting a component into one of those layers makes it easy to ensure that components overlap properly, without having to worry about specifying numbers for specific depths:
DEFAULT_LAYER
The standard layer, where most components go. This the bottommost layer.
PALETTE_LAYER
The palette layer sits over the default layer. Useful for floating toolbars and palettes, so they can be positioned above other components.
MODAL_LAYER
The layer used for modal dialogs. They will appear on top of any toolbars, palettes, or standard components in the container.
POPUP_LAYER
The popup layer displays above dialogs. That way, the popup windows associated with combo boxes, tooltips, and other help text will appear above the component, palette, or dialog that generated them.
DRAG_LAYER
When dragging a component, reassigning it to the drag layer ensures that it is positioned over every other component in the container. When finished dragging, it can be reassigned to its normal layer.
The JLayeredPane methods moveToFront(Component), moveToBack(Component) and setPosition can be used to reposition a component within its layer. The setLayer method can also be used to change the component's current layer.

Details

JLayeredPane manages its list of children like Container, but allows for the definition of a several layers within itself. Children in the same layer are managed exactly like the normal Container object, with the added feature that when children components overlap, children in higher layers display above the children in lower layers.

Each layer is a distinct integer number. The layer attribute can be set on a Component by passing an Integer object during the add call.
For example: 

layeredPane.add(child, JLayeredPane.DEFAULT_LAYER);
 or
     layeredPane.add(child, new Integer(10));
The layer attribute can also be set on a Component by calling
layeredPaneParent.setLayer(child, 10)
on the JLayeredPane that is the parent of component. The layer should be set before adding the child to the parent.

Higher number layers display above lower number layers. So, using numbers for the layers and letters for individual components, a representative list order would look like this:

5a, 5b, 5c, 2a, 2b, 2c, 1a
where the leftmost components are closest to the top of the display.

A component can be moved to the top or bottom position within its layer by calling moveToFront or moveToBack.

The position of a component within a layer can also be specified directly. Valid positions range from 0 up to one less than the number of components in that layer. A value of -1 indicates the bottommost position. A value of 0 indicates the topmost position. Unlike layer numbers, higher position values are lower in the display. 

Note: This sequence (defined by java.awt.Container) is the reverse of the layer numbering sequence. Usually though, you will use moveToFront, moveToBack, and setLayer.
Here are some examples using the method add(Component, layer, position): Calling add(5x, 5, -1) results in:
5a, 5b, 5c, 5x, 2a, 2b, 2c, 1a
Calling add(5z, 5, 2) results in:
5a, 5b, 5z, 5c, 5x, 2a, 2b, 2c, 1a
Calling add(3a, 3, 7) results in:
5a, 5b, 5z, 5c, 5x, 3a, 2a, 2b, 2c, 1a
Using normal paint/event mechanics results in 1a appearing at the bottom and 5a being above all other components.

Note: that these layers are simply a logical construct and LayoutManagers will affect all child components of this container without regard for layer settings.

Warning: Swing is not thread safe. For more information see Swing's Threading Policy.

Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

Nested Classes

Modifier and Type Class and Description
protected class  JLayeredPane.AccessibleJLayeredPane

This class implements accessibility support for the JLayeredPane class.

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

Fields

Modifier and Type Field and Description
static Integer DEFAULT_LAYER

Convenience object defining the Default layer.
static Integer DRAG_LAYER

Convenience object defining the Drag layer.
static Integer FRAME_CONTENT_LAYER

Convenience object defining the Frame Content layer.
static String LAYER_PROPERTY

Bound property
static Integer MODAL_LAYER

Convenience object defining the Modal layer.
static Integer PALETTE_LAYER

Convenience object defining the Palette layer.
static Integer POPUP_LAYER

Convenience object defining the Popup layer.

Fields inherited from class javax.swing.JComponent

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

accessibleContext, 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

Constructors

Constructor and Description
JLayeredPane()

Create a new JLayeredPane

Methods

Modifier and Type Method and Description
protected void addImpl(Component comp, Object constraints, int index)

Adds the specified component to this container at the specified index.
AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this JLayeredPane.
int getComponentCountInLayer(int layer)

Returns the number of children currently in the specified layer.
Component[] getComponentsInLayer(int layer)

Returns an array of the components in the specified layer.
protected Hashtable<Component,Integer> getComponentToLayer()

Returns the hashtable that maps components to layers.
int getIndexOf(Component c)

Returns the index of the specified Component.
int getLayer(Component c)

Returns the layer attribute for the specified Component.
static int getLayer(JComponent c)

Gets the layer property for a JComponent, it does not cause any side effects like setLayer().
static JLayeredPane getLayeredPaneAbove(Component c)

Convenience method that returns the first JLayeredPane which contains the specified component.
protected Integer getObjectForLayer(int layer)

Returns the Integer object associated with a specified layer.
int getPosition(Component c)

Get the relative position of the component within its layer.
int highestLayer()

Returns the highest layer value from all current children.
protected int insertIndexForLayer(int layer, int position)

Primitive method that determines the proper location to insert a new child based on layer and position requests.
boolean isOptimizedDrawingEnabled()

Returns false if components in the pane can overlap, which makes optimized drawing impossible.
int lowestLayer()

Returns the lowest layer value from all current children.
void moveToBack(Component c)

Moves the component to the bottom of the components in its current layer (position -1).
void moveToFront(Component c)

Moves the component to the top of the components in its current layer (position 0).
void paint(Graphics g)

Paints this JLayeredPane within the specified graphics context.
protected String paramString()

Returns a string representation of this JLayeredPane.
static void putLayer(JComponent c, int layer)

Sets the layer property on a JComponent.
void remove(int index)

Remove the indexed component from this pane.
void removeAll()

Removes all the components from this container.
void setLayer(Component c, int layer)

Sets the layer attribute on the specified component, making it the bottommost component in that layer.
void setLayer(Component c, int layer, int position)

Sets the layer attribute for the specified component and also sets its position within that layer.
void setPosition(Component c, int position)

Moves the component to position within its current layer, where 0 is the topmost position within the layer and -1 is the bottommost position.

Methods inherited from class javax.swing.JComponent

addAncestorListener, addNotify, 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, hide, isDoubleBuffered, isLightweightComponent, isManagingFocus, isOpaque, isPaintingForPrint, isPaintingOrigin, isPaintingTile, isRequestFocusEnabled, isValidateRoot, paintBorder, paintChildren, paintComponent, paintImmediately, paintImmediately, print, printAll, printBorder, printChildren, printComponent, processComponentKeyEvent, processKeyBinding, processKeyEvent, processMouseEvent, processMouseMotionEvent, putClientProperty, registerKeyboardAction, registerKeyboardAction, removeAncestorListener, removeNotify, removeVetoableChangeListener, repaint, repaint, requestDefaultFocus, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, resetKeyboardActions, reshape, revalidate, scrollRectToVisible, setActionMap, setAlignmentX, setAlignmentY, setAutoscrolls, setBackground, setBorder, setComponentPopupMenu, setDebugGraphicsOptions, setDefaultLocale, setDoubleBuffered, setEnabled, setFocusTraversalKeys, setFont, setForeground, setInheritsPopupMenu, setInputMap, setInputVerifier, setMaximumSize, setMinimumSize, setNextFocusableComponent, setOpaque, setPreferredSize, setRequestFocusEnabled, setToolTipText, setTransferHandler, setUI, setVerifyInputWhenFocusTarget, setVisible, unregisterKeyboardAction, update, updateUI

Methods inherited from class java.awt.Container

add, add, add, add, add, addContainerListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, countComponents, deliverEvent, doLayout, 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, setLayout, 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, 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

Fields

DEFAULT_LAYER

public static final Integer DEFAULT_LAYER

Convenience object defining the Default layer. Equivalent to new Integer(0).

PALETTE_LAYER

public static final Integer PALETTE_LAYER

Convenience object defining the Palette layer. Equivalent to new Integer(100).

public static final Integer MODAL_LAYER

Convenience object defining the Modal layer. Equivalent to new Integer(200).

public static final Integer POPUP_LAYER

Convenience object defining the Popup layer. Equivalent to new Integer(300).

DRAG_LAYER

public static final Integer DRAG_LAYER

Convenience object defining the Drag layer. Equivalent to new Integer(400).

FRAME_CONTENT_LAYER

public static final Integer FRAME_CONTENT_LAYER

Convenience object defining the Frame Content layer. This layer is normally only use to position the contentPane and menuBar components of JFrame. Equivalent to new Integer(-30000).

See Also:
JFrame

LAYER_PROPERTY

public static final String LAYER_PROPERTY

Bound property

See Also:
Constant Field Values

Constructors

JLayeredPane

public JLayeredPane()

Create a new JLayeredPane

Methods

addImpl

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

Description copied from class: Container

Adds the specified component to this container at the specified index. This method also notifies the layout manager to add the component to this container's layout using the specified constraints object via the addLayoutComponent method.

The constraints are defined by the particular layout manager being used. For example, the BorderLayout class defines five constraints: BorderLayout.NORTH, BorderLayout.SOUTH, BorderLayout.EAST, BorderLayout.WEST, and BorderLayout.CENTER.

The GridBagLayout class requires a GridBagConstraints object. Failure to pass the correct type of constraints object results in an IllegalArgumentException.

If the current layout manager implements LayoutManager2, then LayoutManager2.addLayoutComponent(Component,Object) is invoked on it. If the current layout manager does not implement LayoutManager2, and constraints is a String, then LayoutManager.addLayoutComponent(String,Component) is invoked on it.

If the component is not an ancestor of this container and has a non-null parent, it is removed from its current parent before it is added to this container.

This is the method to override if a program needs to track every add request to a container as all other add methods defer to this one. An overriding method should usually include a call to the superclass's version of the method: 

super.addImpl(comp, constraints, index)

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 display the added component.

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
See Also:
Container.add(Component), Container.add(Component, int), Container.add(Component, java.lang.Object), Container.invalidate(), LayoutManager, LayoutManager2

remove

public void remove(int index)

Remove the indexed component from this pane. This is the absolute index, ignoring layers.

Overrides:
remove in class Container
Parameters:
index - an int specifying the component to remove
See Also:
getIndexOf(java.awt.Component)

removeAll

public void removeAll()

Removes all the components from this container.

Overrides:
removeAll in class Container
Since:
1.5
See Also:
Container.add(java.awt.Component), Container.remove(int), Container.invalidate()

isOptimizedDrawingEnabled

public boolean isOptimizedDrawingEnabled()

Returns false if components in the pane can overlap, which makes optimized drawing impossible. Otherwise, returns true.

Overrides:
isOptimizedDrawingEnabled in class JComponent
Returns:
false if components can overlap, else true
See Also:
JComponent.isOptimizedDrawingEnabled()

putLayer

public static void putLayer(JComponent c,
                            int layer)

Sets the layer property on a JComponent. This method does not cause any side effects like setLayer() (painting, add/remove, etc). Normally you should use the instance method setLayer(), in order to get the desired side-effects (like repainting).

Parameters:
c - the JComponent to move
layer - an int specifying the layer to move it to
See Also:
setLayer(java.awt.Component, int)

getLayer

public static int getLayer(JComponent c)

Gets the layer property for a JComponent, it does not cause any side effects like setLayer(). (painting, add/remove, etc) Normally you should use the instance method getLayer().

Parameters:
c - the JComponent to check
Returns:
an int specifying the component's layer

getLayeredPaneAbove

public static JLayeredPane getLayeredPaneAbove(Component c)

Convenience method that returns the first JLayeredPane which contains the specified component. Note that all JFrames have a JLayeredPane at their root, so any component in a JFrame will have a JLayeredPane parent.

Parameters:
c - the Component to check
Returns:
the JLayeredPane that contains the component, or null if no JLayeredPane is found in the component hierarchy
See Also:
JFrame, JRootPane

setLayer

public void setLayer(Component c,
                     int layer)

Sets the layer attribute on the specified component, making it the bottommost component in that layer. Should be called before adding to parent.

Parameters:
c - the Component to set the layer for
layer - an int specifying the layer to set, where lower numbers are closer to the bottom

setLayer

public void setLayer(Component c,
                     int layer,
                     int position)

Sets the layer attribute for the specified component and also sets its position within that layer.

Parameters:
c - the Component to set the layer for
layer - an int specifying the layer to set, where lower numbers are closer to the bottom
position - an int specifying the position within the layer, where 0 is the topmost position and -1 is the bottommost position

getLayer

public int getLayer(Component c)

Returns the layer attribute for the specified Component.

Parameters:
c - the Component to check
Returns:
an int specifying the component's current layer

getIndexOf

public int getIndexOf(Component c)

Returns the index of the specified Component. This is the absolute index, ignoring layers. Index numbers, like position numbers, have the topmost component at index zero. Larger numbers are closer to the bottom.

Parameters:
c - the Component to check
Returns:
an int specifying the component's index

moveToFront

public void moveToFront(Component c)

Moves the component to the top of the components in its current layer (position 0).

Parameters:
c - the Component to move
See Also:
setPosition(Component, int)

moveToBack

public void moveToBack(Component c)

Moves the component to the bottom of the components in its current layer (position -1).

Parameters:
c - the Component to move
See Also:
setPosition(Component, int)

setPosition

public void setPosition(Component c,
                        int position)

Moves the component to position within its current layer, where 0 is the topmost position within the layer and -1 is the bottommost position.

Note: Position numbering is defined by java.awt.Container, and is the opposite of layer numbering. Lower position numbers are closer to the top (0 is topmost), and higher position numbers are closer to the bottom.

Parameters:
c - the Component to move
position - an int in the range -1..N-1, where N is the number of components in the component's current layer

getPosition

public int getPosition(Component c)

Get the relative position of the component within its layer.

Parameters:
c - the Component to check
Returns:
an int giving the component's position, where 0 is the topmost position and the highest index value = the count count of components at that layer, minus 1
See Also:
getComponentCountInLayer(int)

highestLayer

public int highestLayer()

Returns the highest layer value from all current children. Returns 0 if there are no children.

Returns:
an int indicating the layer of the topmost component in the pane, or zero if there are no children

lowestLayer

public int lowestLayer()

Returns the lowest layer value from all current children. Returns 0 if there are no children.

Returns:
an int indicating the layer of the bottommost component in the pane, or zero if there are no children

getComponentCountInLayer

public int getComponentCountInLayer(int layer)

Returns the number of children currently in the specified layer.

Parameters:
layer - an int specifying the layer to check
Returns:
an int specifying the number of components in that layer

getComponentsInLayer

public Component[] getComponentsInLayer(int layer)

Returns an array of the components in the specified layer.

Parameters:
layer - an int specifying the layer to check
Returns:
an array of Components contained in that layer

paint

public void paint(Graphics g)

Paints this JLayeredPane within the specified graphics context.

Overrides:
paint in class JComponent
Parameters:
g - the Graphics context within which to paint
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)

getComponentToLayer

protected Hashtable<Component,Integer> getComponentToLayer()

Returns the hashtable that maps components to layers.

Returns:
the Hashtable used to map components to their layers

getObjectForLayer

protected Integer getObjectForLayer(int layer)

Returns the Integer object associated with a specified layer.

Parameters:
layer - an int specifying the layer
Returns:
an Integer object for that layer

insertIndexForLayer

protected int insertIndexForLayer(int layer,
                                  int position)

Primitive method that determines the proper location to insert a new child based on layer and position requests.

Parameters:
layer - an int specifying the layer
position - an int specifying the position within the layer
Returns:
an int giving the (absolute) insertion-index
See Also:
getIndexOf(java.awt.Component)

paramString

protected String paramString()

Returns a string representation of this JLayeredPane. 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 JComponent
Returns:
a string representation of this JLayeredPane.

getAccessibleContext

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this JLayeredPane. For layered panes, the AccessibleContext takes the form of an AccessibleJLayeredPane. A new AccessibleJLayeredPane instance is created if necessary.

Specified by:
getAccessibleContext in interface Accessible
Overrides:
getAccessibleContext in class Component
Returns:
an AccessibleJLayeredPane that serves as the AccessibleContext of this JLayeredPane

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