JFrame f = new JFrame("Vertical BoxLayout-managed container");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container pane = new BoxPanel();
f.setContentPane(pane);
pane.setLayout(new BoxLayout(pane, BoxLayout.Y_AXIS));
for (float align = 0.0f; align <= 1.0f; align += 0.25f) {
JButton button = new JButton("X Alignment = " + align);
button.setAlignmentX(align);
pane.add(button);
pane.add(Box.createVerticalGlue());
}
f.setSize(400, 300);
f.setVisible(true);
}
}
Executing this code produces results like those shown below, where the extra vertical space is distributed
evenly to each of the glue components:
As mentioned earlier, extra vertical space is distributed by a vertical BoxLayout based on the difference
between a component's maximum vertical size and its preferred vertical size. As you might guess, glue
components are simply "dummy" components with a large maximum size and a minimum size of 0, so in
many cases, all extra space will be assigned to them. However, as we saw earlier with JTextField
instances, it's possible for other components with large maximum sizes to accidentally be made
inappropriately large by a BoxLayout, and this can occur even when glue components are used.
Struts
One definition of the word "strut" in Webster's New World dictionary is, "a brace fitted into a framework to
resist pressure in the direction of its length", and unlike glue components, struts are appropriately named.
Struts are similar to rigid areas, but with an important difference: instead of specifying both the width and
height of the component, you only specify a strut's size in one dimension.
Specifically, you specify the width when you call createHorizontalStrut() and the height when
calling createVerticalStrut(). The strut uses the value you specify for its minimum, preferred, and
maximum size in that dimension, and uses 0 for the other dimension when setting its minimum and preferred
size. However, when setting the maximum size, Box uses a very large value for the remaining dimension
(width for a vertical box, height for a horizontal box), and this can cause undesirable results. Specifically, the
presence of a very large strut component in the BoxLayout can result in its container being assigned a size
that's larger than what was intended.
Since rigid areas can provide the same functionality and because there is a potential problem associated with
the use of struts, you should avoid struts and use rigid areas instead.
Stop by in one week for the next installment!
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