Slow pack() problem; is there a workaround? (was 'Odd delay on first pack()

Question

I've run into a rather perplexing problem with pack(). When I pack() a visible frame after re-sizing a panel within it, pack takes over FIVE seconds, compared to one second to create the gui in the first place, including a pack(). Subsequent resize-repack calls are very fast. Here's a test program that illustrates the problem:
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class Test implements ActionListener {   
    boolean isOpen;
    Dimension prefD;
    JFrame f;
    JPanel pan1;
    long tm; /* All times in milliseconds. */
    public Test() {
        elapsedTime();
        f = new JFrame();      
            // The main panel
        JPanel pan = new JPanel();
        pan.setLayout(new BoxLayout(pan,BoxLayout.Y_AXIS));                       
        f.getContentPane().add(pan);               
            // Add the button in a panel
        JButton b = new JButton("b");
        b.addActionListener(this);
        pan.add(b);
            // Add a label in another panel
        pan1 = new JPanel();
        pan1.setLayout(new BoxLayout(pan1,BoxLayout.Y_AXIS));
        pan.add(pan1);
        pan1.add(new JLabel("This is pan 1"));
        isOpen = true;
        f.pack();
        prefD =  new Dimension(pan1.getPreferredSize()); // Save this size
        f.setVisible(true);
        System.out.println("Time elapsed in initially creating the gui: "
                           + elapsedTime());
    public void actionPerformed(ActionEvent e) {
        if ( isOpen ) {  // Hide the second panel       
            elapsedTime();
            pan1.setPreferredSize(new Dimension(prefD.width,0));          
            pan1.setSize(new Dimension(prefD.width,0));                      
            System.out.println("Time to resize the panel: " + elapsedTime());           
            f.pack();
            System.out.println("Time to pack(): " + elapsedTime()); 
            isOpen = false;
        else { // Show the lower panel
            elapsedTime();
            pan1.setSize(prefD);
            pan1.setPreferredSize(prefD);
            System.out.println("Time to resize the panel: " + elapsedTime());      
            f.pack();
            System.out.println("Time to pack(): " + elapsedTime()); 
            isOpen = true;
    long elapsedTime() {
        long cur = System.currentTimeMillis();
        long elapsed = cur - tm;
        tm = cur;
        return(elapsed);
    public static void main(String[] argv) {
        new Test();
}When I run this test, the times from hitting the button six times are:
Time elapsed in initially creating the gui: 1260
Time to resize the panel: 0
Time to pack(): 5004
Time to resize the panel: 0
Time to pack(): 3
Time to resize the panel: 1
Time to pack(): 3
Time to resize the panel: 0
Time to pack(): 3
Time to resize the panel: 0
Time to pack(): 3
Time to resize the panel: 0
Time to pack(): 3If I set the frame invisible before the pack and visible again after, the time delay disappears, but of course this is not an adequate solution.
I'd appreciate an suggestion for a workaround, or any ideas about what the problem is. I'm pretty much stuck.
Thanks,
bw

Answer 1

OS: Linux, SuSE 8.0, kernel 2.4.18-4GB
JDK: I've tried this with two versions of 1.4.1
java version "1.4.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1-b21)
Java HotSpot(TM) Client VM (build 1.4.1-b21, mixed mode)
and
java version "1.4.1"
Java(TM) 2 Runtime Environment, Standard Edition (build Blackdown-1.4.1-beta)
Java HotSpot(TM) Client VM (build Blackdown-1.4.1-beta, mixed mode)
moi@bearblue:/usr/local
These yield the same problem (of course they are closely related).
It turns out that the problem does NOT occur with an old 1.3.1 version:
java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1)
Classic VM (build 1.3.1, J2RE 1.3.1 IBM build cxia32131-20020410 (JIT enabled: jitc))