Building graphical user interfaces - Objects First with Java: A Practical Introduction Using BlueJ - page 403

So far, our frame uses a BorderLayout , where the WEST area is empty. We can use this
area to add our toolbar buttons. There is one small problem, though. The WEST area of a
BorderLayout can hold only one component, but we have two buttons.

The solution is simple. We add a JPanel to the frame's WEST area (as we know, a JPanel
is a container), and then stick the two buttons into the JPanel . Code 11.14 shows the code to
do this.

Code 11.14
Adding a toolbar panel
with two buttons

// Create the toolbar with the buttons
JPanel toolbar = new JPanel();

smallerButton = new JButton( "Smaller" );
toolbar.add(smallerButton);

largerButton = new JButton( "Larger" );
toolbar.add(largerButton);

contentPane.add(toolbar, BorderLayout.WEST);

Exercise 11.45 Add two buttons labeled Larger and Smaller to your latest version of the
project, using code similar to the one above. Test it. What do you observe?

When we try this out, we see that it works partially but does not look as expected. The reason
is that a JPanel uses, by default, a FlowLayout , and a FlowLayout arranges its components
horizontally. We would like them arranged vertically.

We can achieve this by using another layout manager. A GridLayout does what we want. When
creating a GridLayout , constructor parameters determine how many rows and columns we
wish to have. A value of zero has a special meaning here, standing for “as many as necessary.”

Thus, we can create a single column GridLayout by using 0 as the number of rows and 1 as
the number of columns. We can then use this GridLayout for our JPanel by using the panel's
setLayout method immediately after creating it:

JPanel toolbar = new JPanel();
toolbar.setLayout(new GridLayout(0, 1));

Alternatively, the layout manager can also be specified as a constructor parameter of the
container:

JPanel toolbar = new JPanel(new GridLayout(0, 1));

Exercise 11.46 Change your code so that your toolbar panel uses a GridLayout , as
discussed above. Test. What do you observe?