Basic Text Components - The Definitive Guide to Java Swing - page 552

nameTextField.addKeyListener(keyListener);
cityTextField.addKeyListener(keyListener);
InputVerifier verifier = new InputVerifier() {
public boolean verify(JComponent input) {
final JTextComponent source = (JTextComponent)input;
String text = source.getText();
if ((text.length() != 0) && !(text.equals("Exit"))) {
JOptionPane.showMessageDialog (source, "Can't leave.",
"Error Dialog", JOptionPane.ERROR_MESSAGE);
return false;
} else {
return true;
}
}
};
nameTextField.setInputVerifier(verifier);
cityTextField.setInputVerifier(verifier);
DocumentListener documentListener = new DocumentListener() {
public void changedUpdate(DocumentEvent documentEvent) {
printIt(documentEvent);
}
public void insertUpdate(DocumentEvent documentEvent) {
printIt(documentEvent);
}
public void removeUpdate(DocumentEvent documentEvent) {
printIt(documentEvent);
}
private void printIt(DocumentEvent documentEvent) {
DocumentEvent.EventType type = documentEvent.getType();
String typeString = null;
if (type.equals(DocumentEvent.EventType.CHANGE)) {
typeString = "Change";
} else if (type.equals(DocumentEvent.EventType.INSERT)) {
typeString = "Insert";
} else if (type.equals(DocumentEvent.EventType.REMOVE)) {
typeString = "Remove";
}
System.out.print("Type : " + typeString + " / ");
Document source = documentEvent.getDocument();
int length = source.getLength();