In this exercise, you will add buttons to the remaining empty cells in the
grid.
Enlarge the layout window to approximately seven inches wide and seven
inches high.
You will be adding a button (approximately 1 inch long) in each cell.
Click the Text Button component in the GUI builder's AWT tab.
Hold down the Control key and click in all empty cells except the
rightmost cell in the last row.
Pressing the Control key allows you to continue adding the selected
component to the grid.
Select the button in the third column of the last row and drag it into the cell on the right.
The button now spans two cells.