The following image shows the relationships between the classes that use root panes.
The "heavyweight" components (those that delegate to a peer, or native component on the host system) are shown with a darker, heavier box. The four heavyweight JFC/Swing containers (JFrame
, JDialog
, JWindow
, and JApplet
) are shown in relation to the AWT classes they extend. These four components are the only heavyweight containers in the Swing library. The lightweight container JInternalFrame
is also shown. All five of these JFC/Swing containers implement the RootPaneContainer
interface, and they all delegate their operations to a JRootPane
(shown with a little "handle" on top). Note: TheJComponent
methodgetRootPane
can be used to obtain theJRootPane
that contains a given component.
JRootPane
. A JRootpane
is made up of a glassPane
, an optional menuBar
, and a contentPane
. (The JLayeredPane
manages the menuBar
and the contentPane
.) The glassPane
sits over the top of everything, where it is in a position to intercept mouse movements. Since the glassPane
(like the contentPane
) can be an arbitrary component, it is also possible to set up the glassPane
for drawing. Lines and images on the glassPane
can then range over the frames underneath without being limited by their boundaries. Although the menuBar
component is optional, the layeredPane
, contentPane
, and glassPane
always exist. Attempting to set them to null
generates an exception.
To add components to the JRootPane
(other than the optional menu bar), you add the object to the contentPane
of the JRootPane
, like this:
rootPane.getContentPane().add(child);The same principle holds true for setting layout managers, removing components, listing children, etc. All these methods are invoked on the
contentPane
instead of on the JRootPane
. Note: The default layout manager for theIf acontentPane
is aBorderLayout
manager. However, theJRootPane
uses a customLayoutManager
. So, when you want to change the layout manager for the components you added to aJRootPane
, be sure to use code like this:rootPane.getContentPane().setLayout(new BoxLayout());
JMenuBar
component is set on the JRootPane
, it is positioned along the upper edge of the frame. The contentPane
is adjusted in location and size to fill the remaining area. (The JMenuBar
and the contentPane
are added to the layeredPane
component at the JLayeredPane.FRAME_CONTENT_LAYER
layer.) The layeredPane
is the parent of all children in the JRootPane
-- both as the direct parent of the menu and the grandparent of all components added to the contentPane
. It is an instance of JLayeredPane
, which provides the ability to add components at several layers. This capability is very useful when working with menu popups, dialog boxes, and dragging -- situations in which you need to place a component on top of all other components in the pane.
The glassPane
sits on top of all other components in the JRootPane
. That provides a convenient place to draw above all other components, and makes it possible to intercept mouse events, which is useful both for dragging and for drawing. Developers can use setVisible
on the glassPane
to control when the glassPane
displays over the other children. By default the glassPane
is not visible.
The custom LayoutManager
used by JRootPane
ensures that:
glassPane
fills the entire viewable area of the JRootPane
(bounds - insets). layeredPane
fills the entire viewable area of the JRootPane
. (bounds - insets) menuBar
is positioned at the upper edge of the layeredPane
. contentPane
fills the entire viewable area, minus the menuBar
, if present. JRootPane
view hierarchy are ignored. If you replace the LayoutManager
of the JRootPane
, you are responsible for managing all of these views. So ordinarily you will want to be sure that you change the layout manager for the contentPane
rather than for the JRootPane
itself!
The painting architecture of Swing requires an opaque JComponent
to exist in the containment hierarchy above all other components. This is typically provided by way of the content pane. If you replace the content pane, it is recommended that you make the content pane opaque by way of setOpaque(true)
. Additionally, if the content pane overrides paintComponent
, it will need to completely fill in the background in an opaque color in paintComponent
.
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 {@link java.beans.XMLEncoder}.
@see JLayeredPane
@see JMenuBar
@see JWindow
@see JFrame
@see JDialog
@see JApplet
@see JInternalFrame
@see JComponent
@see BoxLayout
@see
Mixing Heavy and Light Components
@author David Kloba
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