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.revalidate() 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....