JScrollPane Doesn't Respond To Client Changes

When a JTextArea is created in a JScrollPane and the contents of the JTextArea change, the JScrollPane's preferred size doesn't change.

In the following code, I create a JScrollPane and a JTextArea as a client. I then, add contents to the JTextArea and call revalidate() on it to let the JScrollPane re-update itself. However, it keeps reporting the same preferred size.
 
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
class c
{
static JScrollPane sp;
static JTextArea ta;
public static void main (String...args)

[Code] ....