Module java.desktop
Package javax.swing

Class JLayeredPane

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

@JavaBean(defaultProperty="accessibleContext")
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.

Example:

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, Integer.valueOf.valueOf(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.

Since:
1.2
  • Field Details

    • DEFAULT_LAYER

      public static final Integer DEFAULT_LAYER
      Convenience object defining the Default layer. Equivalent to Integer.valueOf(0).
    • PALETTE_LAYER

      public static final Integer PALETTE_LAYER
      Convenience object defining the Palette layer. Equivalent to Integer.valueOf(100).
    • DRAG_LAYER

      public static final Integer DRAG_LAYER
      Convenience object defining the Drag layer. Equivalent to Integer.valueOf(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 Integer.valueOf(-30000).
      See Also:
      JFrame
    • LAYER_PROPERTY

      public static final String LAYER_PROPERTY
      Bound property
      See Also:
      Constant Field Values
  • Constructor Details

    • JLayeredPane

      public JLayeredPane()
      Create a new JLayeredPane
  • Method Details

    • 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

      @BeanProperty(bound=false) 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

      @BeanProperty(bound=false) 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