JScrollPane visible part refresh rate problem

Question

I am writing an application that reads image and displays it in a JScrollPane via JPanel. It also has JSlider to set displayed image focus. The problem is that sometimes when big image is loaded and user changes seen part via scrollbars, the JScollPane refresh takes about 10 sec. The question is: How to make JScrollPane's content refresh/repaint only the part that is visible. The code is:
import java.awt.image.BufferedImage;
import java.io.*;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import javax.swing.event.*;
public class Main extends JFrame{
    private BufferedImage image;
    private JScrollPane sPane;
    private ImagePanel iPanel;
    private JSlider slider;
    private Container contentPane;
    public Main() {
        try {
            image = ImageIO.read(new File("c:\\pict\\img.JPG"));
        } catch (IOException ioe){
            ioe.printStackTrace();
            System.exit(1);
        slider = new JSlider(JSlider.HORIZONTAL,1,3,1);
        slider.setMinorTickSpacing(1);
        slider.setMajorTickSpacing(1);
        slider.setSnapToTicks(true);
        slider.addChangeListener(new ChangeListener() {
            public void stateChanged(ChangeEvent e) {
                iPanel.setImageFocus(slider.getValue());
                invalidate();
        iPanel = new ImagePanel(image);
        sPane = new JScrollPane(iPanel,
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
                JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        contentPane = this.getContentPane();
        contentPane.add(slider,BorderLayout.NORTH);
        contentPane.add(sPane,BorderLayout.CENTER);
        setExtendedState(JFrame.MAXIMIZED_BOTH);
        setDefaultCloseOperation(3);
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Main().setVisible(true);
class ImagePanel extends JPanel{
    private Image img;
    private Dimension imageSize;
    public ImagePanel(Image img){
        this.img = img;
        imageSize = new Dimension(img.getWidth(null),img.getHeight(null));
    public void setImage(Image img){
        this.img = img;
    public void setImageFocus(int focus){
        if (this!=null){
            getGraphics().clearRect(0,0,imageSize.width,imageSize.height);
        switch (focus){
            case 1:
                imageSize = new Dimension(img.getWidth(null),img.getHeight(null));
                break;
            case 2:
                imageSize = new Dimension(2*img.getWidth(null),2*img.getHeight(null));
                break;
            case 3:
                imageSize = new Dimension(3*img.getWidth(null),3*img.getHeight(null));
                break;
            default:
                imageSize = new Dimension(0,0);
        setSize(imageSize);
        setPreferredSize(imageSize);
        repaint();
        ((JScrollPane)getParent().getParent()).revalidate();
    public void paintComponent(Graphics g){
        JScrollPane sp = (JScrollPane)getParent().getParent();
        g.clearRect(sp.getX(),sp.getY(),sp.getWidth(),sp.getHeight());
        g.drawImage(img,0,0,imageSize.width,imageSize.height,null);
}Thanks,

Answer 1

Sure
DefaultTableModel dtm = new DefaultTableModel(vec, header);
          jt0 = new JTable(dtm);
          jt0.getTableHeader().setReorderingAllowed(false);
          jt0.setFont(new Font("Tahoma", Font.PLAIN, 12));
          jt0.getTableHeader().setFont(new java.awt.Font("Tahoma", java.awt.Font.BOLD, 12));
          jt0.setRowHeight(18);
        jt0.setPreferredScrollableViewportSize(new Dimension(500, jt0.getRowCount() * jt0.getRowHeight()));
        jt0.setFillsViewportHeight(false);
          jsp0 = new JScrollPane(jt0);
GridBagConstraints gbc = new GridBagConstraints(); 
        gbc.insets = new Insets(2,1,2,1); 
        gbc.weightx = 1.0; 
        gbc.weighty = 1.0; 
        JPanel p0 = new JPanel(new GridBagLayout()); 
        gbc.fill = gbc.HORIZONTAL;
        p0.add(jsp0, gbc);
          JButton jb1 = new JButton("add row");
          jb1.setSize(40, 18);
jb1.addActionListener(new java.awt.event.ActionListener() {
               public void actionPerformed(java.awt.event.ActionEvent e) {
                    dtm.addRow(new Object[]{....});
//                    jt0.scrollRectToVisible(jt0.getCellRect(jt0.getModel().getRowCount()-1, 1, false));
//                    jt0.setRowSelectionInterval(jt0.getModel().getRowCount()-1, jt0.getModel().getRowCount()-1);
    public class SizeX extends JScrollPane {
         public Dimension getPreferredSize() {
              Dimension size = super.getPreferredSize();
              size.height -= getViewport().getPreferredSize().height;
              Component view = getViewport().getView();
              if(view != null)
              size.height += view.getPreferredSize().height;
              return size;
    }