Relevance of jseparator.revalidate() statement

[anurag275125]

Hello Bytes.com members.....

I write a swing program that automatically re-size the separator. But I didn't understand the significance of jseparator.reva lidate() line in the code.
here is the code..........

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/* <applet
code=resize_separator.class
width=600
height=600
>
</applet> */
public class resize_separator extends JApplet implements ComponentListener
{
	JSeparator js=new JSeparator(JSeparator.VERTICAL);
	Dimension d=js.getPreferredSize();
	public void init()
	{
		Container c=getContentPane();
		c.setLayout(new FlowLayout());
		c.add(new JTextField("Hello from swing!",30));
		c.add(js);
		c.add(new JTextField("Hello from swing!",30));
		addComponentListener(this);
	}
	public void componentShown(ComponentEvent e)
	{
		js.setPreferredSize(new Dimension(d.width,getSize().height));
		js.revalidate();       // please explain the line
	}
	public void componentResized(ComponentEvent e)
	{
		js.setPreferredSize(new Dimension(d.width,getSize().height));
		js.revalidate();
	}
	public void componentMoved(ComponentEvent e){}
	public void componentHidden(ComponentEvent e){}
}

can you please explain the statement??

thanks....