Java Reference
In-Depth Information
generated the event each time
actionPerformed
is called. The
event source
is the compo-
nent with which the user interacted. When the user presses
Enter
while a text field or the
password field
has the focus
, the system creates a unique
ActionEvent
object that contains
information about the event that just occurred, such as the event source and the text in the
text field. The system passes this
ActionEvent
object to the event listener's
actionPer-
formed
method. Line 56 declares the
String
that will be displayed. The variable is initialized
with the
empty string
—a
String
containing no characters. The compiler requires the vari-
able to be initialized in case none of the branches of the nested
if
in lines 59-76 executes.
ActionEvent
method
getSource
(called in lines 59, 64, 69 and 74) returns a reference
to the event source. The condition in line 59 asks, “Is the event source
textField1
?” This
condition compares references with the
==
operator to determine if they refer to the same
object. If they
both
refer to
textField1
, the user pressed
Enter
in
textField1
. Then, lines
60-61 create a
String
containing the message that line 79 displays in a message dialog.
Line 61 uses
ActionEvent
method
getActionCommand
to obtain the text the user typed in
the text field that generated the event.
In this example, we display the text of the password in the
JPasswordField
when the
user presses
Enter
in that field. Sometimes it's necessary to programatically process the
characters in a password. Class
JPasswordField
method
getPassword
returns the pass-
word's characters as an array of type
char
.
Class
TextFieldTest
Class
TextFieldTest
(Fig. 12.10) contains the
main
method that executes this application
and displays an object of class
TextFieldFrame
. When you execute the application, even
the uneditable
JTextField
(
textField3
) can generate an
ActionEvent
. To test this, click
the text field to give it the focus, then press
Enter
. Also, the actual text of the password is
displayed when you press
Enter
in the
JPasswordField
. Of course, you would normally
not display the password!
1
// Fig. 12.10: TextFieldTest.java
2
// Testing TextFieldFrame.
3
import
javax.swing.JFrame;
4
5
public
class
TextFieldTest
6
{
7
public
static
void
main(String[] args)
8
{
9
TextFieldFrame textFieldFrame =
new
TextFieldFrame();
10
textFieldFrame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE
);
11
textFieldFrame.setSize(
350
,
100
);
12
textFieldFrame.setVisible(
true
);
13
}
14
}
// end class TextFieldTest
Fig. 12.10
|
Testing
TextFieldFrame
. (Part 1 of 2.)
