Core JFC Java Foundation Classes 2nd edition - Read

456 Chapter 5 Keyboard Handling, Actions, and Scrolling
Listing 5-1 Automatic focus handling (continued)
public static void main(String[] args) {
FocusExamplel f = new FocusExamplel();
f .packO ;
f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent evt) {
System.exit(0);
}
});
f.setVisible(true);
}
private JButton b; // The button
private JTextField t; // The text field
Run this program using the command
j ava JFCBook.Chapters.FocusExamplel
and try it without using the mouse. You will find that the text area is ready to
receive input straight away, because the initial focus has been assigned to this
component automatically. Now type something and press the return key and
your text will appear on the caption bar. So far, so good. Now type some more
into the text area. Suppose that you wanted to use the Clear button to discard
the text you have just typed. With the mouse, you simply move the
pointer over the button and click, but if you can't use the mouse, how can you
get to the button?
The focus can be moved between components by using Tab to go forward
and Shift-Tab to move backward. In this case, since there are only two
components, you can use either key to move to the button. When you get the
focus onto the button, notice that it highlights itself—this is typical visual
feedback when a component has the focus. Now that you're over the button,
how do you "click" it? The JButton class is keyboard-aware: if you press the
space bar, it acts as if you had clicked it with the mouse. Do this now and
your text will disappear. To type some more text, just tab back to the text area
and notice that the button loses its highlighting.
Using the requestFocus Method
What you have just seen was free functionality: the correct component got
the focus when the application started and both components reacted prop-