Java Reference
In-Depth Information
Window Panes
When you want to add GUI components or draw in a window displayed from a
JFrame
object, you
add the components to, or draw on, a
window pane
that is managed by the
JFrame
object. The same
goes for an applet. Broadly speaking, window panes are container objects that represent an area of a
window, and they come in several different types.
You will use a
window pane called
the
content pane
most of the time, but
there are others. The
relationship between
the
contentPane
object, other window
panes, and the
application window
itself is shown here.
JFrame Window
The area of the window below the title bar
corresponds to a JRootPane Object
LayeredPane object of type JLayeredPane
contentPane object of type JInternalPane
The contentPane is where you normally add components
other than a menubar to a window. A reference to
contentPane is returned by the getContentPane() member
of the JFrame object
As you see, the area below the title bar in a
JFrame
window corresponds to a
JRootPane
object. This
contains another pane, the
layeredPane
object in the illustration, which is of type
JLayeredPane
.
This pane corresponds to the whole of the area occupied by the
JRootPane
object in the window and
manages the menu bar if the window has one. The area in the
layeredPane
below the menu bar
corresponds to the
contentPane
object, and it's here that you typically add GUI components. You
also display text or do any drawing in the area covered by the content pane.
The
layeredPane
object has special properties for advanced applications that permit groups of
components to be managed in separate layers that overlay one another within the pane. With this
capability you can control how components are displayed relative to one another, because the layers are
displayed in a particular order from back to front. The components in a layer at the front will appear on
the screen in front of those in a layer that is towards the back.
There is also an additional pane not shown in the diagram. This is the
glassPane
object, and this also
corresponds to the complete
JRootPane
area. The contents of the
glassPane
object displays on top
of all the other panes, so this is used to display components that you always want to display on top of
anything else displayed in the window - such as pop-up menus. You can also use the
glassPane
to
display graphics that need to be updated relatively frequently - such as when you create an animation.
When part of what is displayed is to be animated, a static background can be displayed independently
via the
contentPane
. Since this doesn't need to be reprocessed each time the animated objects need
to be redrawn, the whole process can be much more efficient.
The
JFrame
class defines methods to provide you with a reference to any of the panes:
