Java Reference
In-Depth Information
Glue
The
for
statement at lines 38-42 adds three
JButton
s to
horizontal2
. Before adding each
button, line 40 adds
horizontal glue
to the container with
static
Box
method
create-
HorizontalGlue
. Horizontal glue is an invisible GUI component that can be used be-
tween fixed-size GUI components to occupy additional space. Normally, extra space
appears to the right of the last horizontal GUI component or below the last vertical one in
a
BoxLayout
. Glue allows the extra space to be placed between GUI components. When
the container is resized, components separated by glue components remain the same size,
but the glue stretches or contracts to occupy the space between them. Class
Box
also de-
clares method
createVerticalGlue
for vertical
BoxLayout
s.
Rigid Areas
The
for
statement at lines 45-49 adds three
JButton
s to
vertical2
. Before each button
is added, line 47 adds a
rigid area
to the container with
static
Box
method
create-
RigidArea
. A rigid area is an invisible GUI component that always has a fixed pixel width
and height. The argument to method
createRigidArea
is a
Dimension
object that speci-
fies the area's width and height.
Setting a
BoxLayout
for a
Container
Lines 52-53 create a
JPanel
object and set its layout to a
BoxLayout
in the conventional
manner, using
Container
method
setLayout
. The
BoxLayout
constructor receives a ref-
erence to the container for which it controls the layout and a constant indicating whether
the layout is horizontal (
BoxLayout.X_AXIS
) or vertical (
BoxLayout.Y_AXIS
).
Adding
Glue
and
JButton
s
The
for
statement at lines 55-59 adds three
JButton
s to
panel
. Before adding each but-
ton, line 57 adds a glue component to the container with
static
Box
method
create-
Glue
. This component expands or contracts based on the size of the
Box
.
Creating the
JTabbedPane
Lines 62-63 create a
JTabbedPane
to display the five containers in this program. The ar-
gument
JTabbedPane.TOP
sent to the constructor indicates that the tabs should appear at
the top of the
JTabbedPane
. The argument
JTabbedPane.SCROLL_TAB_LAYOUT
specifies
that the tabs should wrap to a new line if there are too many to fit on one line.
Attaching the
Box
Containers and
JPanel
to the
JTabbedPane
The
Box
containers and the
JPanel
are attached to the
JTabbedPane
at lines 66-70. Try
executing the application. When the window appears, resize the window to see how the
glue components, strut components and rigid area affect the layout on each tab.
One of the most powerful predefined layout managers is
GridBagLayout
(in package
ja-
va.awt
). This layout is similar to
GridLayout
in that it arranges components in a grid, but
it's more flexible. The components can vary in size (i.e., they can occupy multiple rows
and columns) and can be added in any order.
The first step in using
GridBagLayout
is determining the appearance of the GUI. For
this step you need only a piece of paper. Draw the GUI, then draw a grid over it, dividing
