This section provides a tutorial example on how to create a text field with an event handler implemented as both the ActionListener listener and the DocumentListener listenser.
As you can see from the previous section, a text field can trigger action events directly.
It can also trigger document events indirectly through its associated document.
Here is a sample program to show you how and when those events are triggered:
/**
* JTextFieldTest.java
* Copyright (c) 2002 by Dr. Herong Yang, http://www.herongyang.com/
*/
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class JTextFieldTest {
public static void main(String[] a) {
JFrame f = new JFrame("Text Field Test");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MyTextField t = new MyTextField(16);
f.getContentPane().add(t,BorderLayout.CENTER);
f.pack();
f.setVisible(true);
}
private static class MyTextField extends JTextField
implements ActionListener, DocumentListener {
static int count = 0;
public MyTextField(int l) {
super(l);
addActionListener(this);
Document doc = this.getDocument();
System.out.println("The document object: "+doc);
doc.addDocumentListener(this);
}
public void actionPerformed(ActionEvent e) {
count++;
System.out.println(count+": Action performed - "+getText());
}
public void insertUpdate(DocumentEvent e) {
count++;
System.out.println(count+": Insert update - "+getText());
}
public void removeUpdate(DocumentEvent e) {
count++;
System.out.println(count+": Remove update - "+getText());
}
public void changedUpdate(DocumentEvent e) {
count++;
System.out.println(count+": Change update - "+getText());
}
}
}
Run this program and do the following in the text field:
Type "h".
Type "i".
Press the backspace key to remove "i".
Type "e".
Press the enter key.
The text field should look like this:
And you should get the following output in the console window:
The document object: javax.swing.text.PlainDocument@4e79f1
1: Insert update - h
2: Insert update - hi
3: Remove update - h
4: Insert update - he
5: Action performed - he
The output confirms that:
TextField class is using PlainDocument as the default document type.
ActionListener is called when the enter key is pressed.
changeUpdate() is not called.
Sample programs listed in this section have been tested with JDK 1.3.1, 1.4.1, 1.5.0, and 1.6.0.
