GridBagConstraints also defines several static fields that contain standard constraint
values, such as GridBagConstraints.CENTER and GridBagConstraints.VERTICAL.
When a component is smaller than its cell, you can use the anchor field to specify where
within the cell the component's top-left corner will be located. There are three types of values
that you can give to anchor. The first are absolute:
GridBagConstraints.CENTER
GridBagConstraints.SOUTH
GridBagConstraints.EAST
GridBagConstraints.SOUTHEAST
GridBagConstraints.NORTH
GridBagConstraints.SOUTHWEST
GridBagConstraints.NORTHEAST
GridBagConstraints.WEST
GridBagConstraints.NORTHWEST
As their names imply, these values cause the component to be placed at the specific locations.
The second type of values that can be given to anchor is relative, which means the
values are relative to the container 's orientation, which might differ for non-Western
languages. The relative values are shown here:
GridBagConstraints.FIRST_LINE_END
GridBagConstraints.LINE_END
GridBagConstraints.FIRST_LINE_START
GridBagConstraints.LINE_START
GridBagConstraints.LAST_LINE_END
GridBagConstraints.PAGE_END
GridBagConstraints.LAST_LINE_START
GridBagConstraints.PAGE_START
Their names describe the placement.
The third type of values that can be given to anchor were added by Java SE 6. They
allow you to position components vertically relative to the baseline of the row. They are
shown here:
GridBagConstraints.BASELINE
GridBagConstraints.BASELINE_LEADING
GridBagConstraints.BASELINE_TRAILING
GridBagConstraints.ABOVE_BASELINE
GridBagConstraints.ABOVE_BASELINE_LEADING GridBagConstraints.ABOVE_BASELINE_TRAILING
GridBagConstraints.BELOW_BASELINE
GridBagConstraints.BELOW_BASELINE_LEADING
GridBagConstraints. BELOW_BASELINE_TRAILING
The horizontal position can be either centered, against the leading edge (LEADING), or
against the trailing edge (TRAILING).
The weightx and weighty fields are both quite important and quite confusing at first
glance. In general, their values determine how much of the extra space within a container
is allocated to each row and column. By default, both these values are zero. When all values
within a row or a column are zero, extra space is distributed evenly between the edges of
the window. By increasing the weight, you increase that row or column's allocation of space
proportional to the other rows or columns. The best way to understand how these values
work is to experiment with them a bit.
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