Swing I - Java - page 929

in which they are added. The following code, taken from the constructor in Display
17.14, creates a new JMenu object named colorMenu and then adds a JMenuItem
labeled "Red" . Other menu items are added in a similar way.

JMenu colorMenu = new JMenu("Add Colors");

JMenuItem greenChoice = new JMenuItem("Green");
greenChoice.addActionListener( this );
colorMenu.add(greenChoice);

Note that, just as we did for buttons in Display 17.11, in Display 17.14 we have
registered the this parameter as an action listener for each menu item. Defining
action listeners and registering listeners for menu items are done in the exact same way
as for buttons. In fact, the syntax is even the same. If you compare Display 17.14 and
Display 17.11, you will see that the definition of the method actionPerformed is the
same in both classes.
You add a JMenuItem to an object of the class JMenu using the method add in
exactly the same way that you add a component, such as a button, to a container
object. Moreover, if you look at the preceding code, you will see that you specify a
string for a JMenuItem in the same way that you specify a string to appear on a button.
A menu bar is a container for menus, typically placed near the top of a window-
ing interface. You add a menu to a menu bar using the method add in the same way
that you add menu items to a menu. The following code from the constructor in
Display 17.14 creates a new menu bar named bar and then adds the menu named
colorMenu to this menu bar:

listeners

menu bar

JMenuBar bar = new JMenuBar();
bar.add(colorMenu);

There are two different ways to add a menu bar to a JFrame . You can use the
method setJMenuBar , as shown in the following code from the constructor in Dis-
play 17.14:

setJMenuBar(bar);

This sets an instance variable of type JMenuBar so that it names the menu bar named
bar . Saying it less formally, this adds the menu bar named bar to the JFrame and
places the menu bar at the top of the JFrame .
Alternatively, you can use the add method to add a menu bar to a JFrame (or to any
other container). You do so in the same way that you add any other component, such as
a label or a button. An example of using add to add a JMenuBar to a JFrame is given in
the file MenuAdd.java on the accompanying CD.

extra code
on CD