Can't show image in the center of the jscrollpane ,any one can help

Question

i write a program to show image in the jscrollpane
i create a class called ImageLabel (it extends jlabel) then i use
ImageLabel im=new ImageLabel(imageicon)
jscrollpane.setViewportView(im);
validate();
repaint();
but it show the image in the left and top corner of the jscrollpane ,not in the center of the jscrollpane
then i change the ImageLabel to JLabel ,:
JLabel im=new JLabel(imageicon);
jscrollpane.setViewportView(im);
validate();
repaint();
it shows the image in the center of the jscrollpane,
but i want to use ImageLabel not jlabel
whats the problem ,any one can help me ,thank you:)

Answer 1

the ZoomLabel is the imagelabel ,and my complete code as follows:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
class ZoomLabel extends JLabel
    private ImageIcon icImage;   
    private int ph,pw,picW,picH;    
    ZoomLabel(ImageIcon ic)   
        super(ic, JLabel.CENTER); 
        icImage = ic;
        pw = picW = ic.getIconWidth(); 
        ph = picH = ic.getIconHeight();
       setSize(pw,ph);
       setPreferredSize(new Dimension(pw,ph));
       repaint();
      validate();
       public void zoom(float scale)    
           ph = Math.round(picH * scale);         
           pw = Math.round(picW * scale);          
           setPreferredSize(new Dimension(pw,ph)); 
           repaint();
         public void paint(Graphics g)     
                 update(g);     
            public synchronized void update(Graphics g)     
            {             g.drawImage(icImage.getImage(),0,0,pw,ph,this); 
  public class ImageShow extends JFrame
              ImageShow()
             ImageIcon ii=new ImageIcon("e:/download/pic/me1.JPG");
               JScrollPane js=new JScrollPane();
               zl=new ZoomLabel(ii);
              js.setViewportView(zl);
              getContentPane().add(js,"Center");
                 js.repaint();
                              js.validate();
              pack();
              setVisible(true);     
         public  static void main(String[] args)
               new ImageShow();
         ZoomLabel zl;
    }