Re: handling resize events with JScrollPane

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;

public class test extends JPanel {
    final BufferedImage image;
    int imageW,imageH;

    public test() throws IOException {
        image = ImageIO.read(new File("kittens.jpg"));
        imageW = image.getWidth();
        imageH = image.getHeight();
        setPreferredSize(new Dimension(imageW,imageH));
    }

    public void paintComponent(Graphics g) {
        int x = Math.max(getWidth() - imageW,0) / 2;
        int y = Math.max(getHeight() - imageH,0) / 2;
        g.drawImage(image,x,y,imageW,imageH,null);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    final test t = new test();
                    final JFrame f = new JFrame();
                    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                    final JScrollPane sp = new JScrollPane(t);
                    f.add(sp,BorderLayout.CENTER);

                    JMenuBar mb = new JMenuBar();
                    f.setJMenuBar(mb);

                    JMenu m = new JMenu("Scale");
                    mb.add(m);

                    final JMenuItem oneX = new JMenuItem("1X");
                    final JMenuItem twoX = new JMenuItem("2X");

                    oneX.setEnabled(false);
                    oneX.addActionListener(new ActionListener() {
                        public void actionPerformed(ActionEvent ae) {
                            oneX.setEnabled(false);
                            twoX.setEnabled(true);
                            t.imageW /= 2;
                            t.imageH /= 2;
                            t.setPreferredSize(
                             new Dimension(t.imageW,t.imageH));
                            t.revalidate();
                            f.repaint();
                        }
                    });
                    m.add(oneX);

                    twoX.addActionListener(new ActionListener() {
                        public void actionPerformed(ActionEvent ae) {
                            twoX.setEnabled(false);
                            oneX.setEnabled(true);
                            t.imageW *= 2;
                            t.imageH *=2;
                            t.setPreferredSize(
                             new Dimension(t.imageW,t.imageH));
                            t.revalidate();
                            f.repaint();
                        }
                    });
                    m.add(twoX);

                    f.pack();
                    f.setVisible(true);
                } catch (IOException ioe) {
                    ioe.printStackTrace();
                }
            }
        });
    }
}