The gridwidth and gridheight fields
specify the number of cells in a row (gridwidth) or
column (gridheight) in the Component's
display area. The mnemonic constant
GridBagConstraints.REMAINDER specifies that the
Component should use all remaining cells in its row (for
gridwidth) or column (for gridheight).
The mnemonic constant GridBagConstraints.RELATIVE
specifies that the Component should fill all but the
last cell in its row (gridwidth) or column
(gridheight).
The calculator's display is four cells wide and one cell high so it's set like this
displayConstraints.gridwidth = 4;
displayConstraints.gridheight = 1;The equals key is two cells high and one wide so it's set like this
equalsConstraints.gridwidth = 1;
equalsConstraints.gridheight = 2;