TextArea and TextField can install
a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the component changes. This is more or less
every time the user hits a key in the component.
The java.awt.event.TextListener interface defines a single method, textValueChanged():
public abstract void textValueChanged(TextEvent te)
You register a TextListener with a TextComponent by calling the component's addTextListener() method. For example,
TextArea password = new TextArea(24)
password.addTextListener(new PasswordChecker());
However, most of the time it's sufficient to just get and set
the text as you need it. It's really quite rare that you need to
process it character by character.
A TextListener can be removed by calling removeTextListener().
public void removeTextListener(TextListener tl)