The gridx and gridy fields specify the x
and y coordinates of the cell at the upper left of the
Component's display area. The upper-left-most cell has
coordinates (0, 0). The mnemonic constant
GridBagConstraints.RELATIVE specifies that the
Component is placed immediately to the right of
(gridx) or immediately below (gridy) the
previous Component added to this container.
The calculator's display starts at the upper left hand corner of
the applet. Thus its gridx and gridy members are set like this
displayConstraints.gridx = 0;
displayConstraints.gridy = 0;The zero key would have
zeroConstraints.gridx = 0;
zeroConstraints.gridy = 5;