Adding a Listener to a JTextComponent

(This slide covered time permitting.)

• In keeping with the Model-View-Controller architecture, we don't exactly add a listener to the JTextComponent itself, we add it to its model.  With text components, this is called a Document interface.
• So, we need to get the Document object from the JTextField object, and add the DocumentListener object to it.  Assume we have a document listener called listener.  We can then add it like so:

txtAddress.getDocument().addDocumentListener(listener);
• The DocumentListener interface has three methods we can use:
• void insertUpdate(DocumentEvent e) is called when the text in the field is updated.  You can put validation logic here.
• void removeUpdate(DocumentEvent e) is called when the text is removed.  You could restore a default value here, or inform the user that the field is required.
• void changeUpdate(DocumentEvent e) is called when other changes occur.  This does not apply to a JTextField.
 More about JTextAreas and JPasswordFields
 

Created by:  Brandan Jones January 4, 2002