Java Reference
In-Depth Information
16.9
If class
A
is an inner class in class
B
, what is the .class file for
A
? If class B contains
two anonymous inner classes, what are the .class file names for these two classes?
✓
✓
Check
Point
16.10
What is wrong in the following code?
import
java.swing.*;
import
java.awt.*;
import
java.awt.event.*;
import
javax.swing.*;
public class
Test
extends
JFrame {
public
Test() {
JButton jbtOK =
new
JButton(
"OK"
);
add(jbtOK);
public class
Test
extends
JFrame {
public
Test() {
JButton jbtOK =
new
JButton(
"OK"
);
add(jbtOK);
jbtOK.addActionListener(
new
ActionListener() {
public void
actionPerformed
(ActionEvent e) {
System.out.println
(jbtOK.getActionCommand());
}
private class
Listener
implements
ActionListener {
public void
actionPerform
(ActionEvent e) {
System.out.println
(jbtOK.getActionCommand());
}
}
// Something missing here
}
}
}
/** Main method omitted */
/** Main method omitted */
}
}
(a)
(b)
16.11
What is the difference between the
setSize(width, height)
method and the
pack()
method in
JFrame
?
Using an inner class or an anonymous inner class is preferred for defining listener
classes.
Key
Point
There are many other ways to define the listener classes. For example, you can rewrite Listing
16.4 by creating just one listener, register the listener with the buttons, and let the listener
detect the event source—that is, which button fires the event—as shown in Listing 16.5.
L
ISTING
16.5
DetectSourceDemo.java
1
import
javax.swing.*;
2
import
java.awt.event.*;
3
4
public class
DetectSourceDemo
extends
JFrame {
5
// Create four buttons
6
private
JButton jbtNew =
new
JButton(
"New"
);
7
private
JButton jbtOpen =
new
JButton(
"Open"
);
8
private
JButton jbtSave =
new
JButton(
"Save"
);
9
private
JButton jbtPrint =
new
JButton(
"Print"
);
10
11
public
DetectSourceDemo() {
12
// Create a panel to hold buttons
13 JPanel panel =
new
JPanel();
14 panel.add(jbtNew);
15 panel.add(jbtOpen);
16 panel.add(jbtSave);
17 panel.add(jbtPrint);
18
