import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JOptionPane;
 
public class PaintExample extends java.awt.Frame {
 
    public PaintExample() {
        initComponents();
    }
 
    private void doSomething() {
        JOptionPane.showMessageDialog(this, "done");
    }
 
    private void formKeyPressed(java.awt.event.KeyEvent evt) {
        repaint();
    }
 
    @Override
    public void paint(Graphics g) {
        // arbitrary long paint process
        int w = getWidth();
        int h = getHeight();
        int reps = 500000;
        g.setColor(Color.BLACK);
        for (int i = 0; i < reps; i++) {
            int y = (int)(i / (float)reps * h);
            g.drawLine(0, y, w, y);
        }
    }
 
    @Override
    public void update(Graphics g) {
        super.update(g);
        doSomething();
    }
 
    private void initComponents() {
        setTitle("PaintExample");
        setMinimumSize(new java.awt.Dimension(400, 400));
        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosing(java.awt.event.WindowEvent evt) {
                exitForm(evt);
            }
        });
        addKeyListener(new java.awt.event.KeyAdapter() {
            public void keyPressed(java.awt.event.KeyEvent evt) {
                formKeyPressed(evt);
            }
        });
 
        pack();
    }
 
    private void exitForm(java.awt.event.WindowEvent evt) {                          
        System.exit(0);
    }                         
 
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new PaintExample().setVisible(true);
            }
        });
    }
 
}