JScrollPane scroll bar trouble on rebuild

Question

I've been working on this for hours (about 4 hours now) without finding the right solution, so maybe someone can help. I searched through a few pages of the forum but didn't see this exact issue. And the tutorial online doesn't help much.
I have a JPanel in a JScrollPane in a JFrame. The JFrame has it's height reduced if its over a particular size (in the test case, it gets reduced). When it first loads, it's fine. However, if I rebuild the whole JFrame (some event causes the JPanel content to change, and refresh() is called again), the window remains the same size but the vertical scroll bar extends off the bottom of the frame. If I manually resize the frame with the mouse (even by 1 pixel), the scroll bar updates and looks correct again. What is the correct way to do this? Calling revalidate() on the JScrollPane after doing the setSize() doesn't do anything. And why does it work the first time when the JFrame is first built through the Constructor?
example code:
public class MyFrame extends JFrame {
    public MyFrame() {
        super();
        refresh();
    private void refresh() {
        JPanel jp = new JPanel();
        jp.setLayout(new SpringLayout());
        // add some stuff to jp
        JScrollPane scrollPane = new JScrollPane(
            JScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,
            JScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED
        scrollPane.getViewport().add(jp);
        setContentPane(scrollPane);
        pack();
        if (getHeight() > MAX_HEIGHT) {
            setSize(getWidth(),MAX_HEIGHT);
}

Answer 1

When you have changed the content, call getRootPane().validate(); instead of pack(), as in this slightly modified version of your sample program:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MyFrame extends JFrame implements ActionListener {
    private static final int MAX_HEIGHT = 100;
    public MyFrame() {
        super();
        refresh(true);
    public static void main(String[] args) {
        MyFrame myFrame = new MyFrame();
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        myFrame.setVisible(true);
    private void refresh(boolean pack) {
        JPanel jp = new JPanel();
        jp.setLayout(new BoxLayout(jp,BoxLayout.Y_AXIS));
        JButton refreshButton = new JButton("Refresh");
        refreshButton.setActionCommand("refresh");
        refreshButton.addActionListener(this);
        jp.add(refreshButton);
        jp.add(new JLabel("Hello"));
        jp.add(new JLabel("There"));
        jp.add(new JLabel("Why"));
        jp.add(new JLabel("Doesn't"));
        jp.add(new JLabel("Refresh"));
        jp.add(new JLabel("Work"));
        JScrollPane scrollPane = new JScrollPane(
            ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,
            ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED
        scrollPane.getViewport().add(jp);
        setContentPane(scrollPane);
        if (pack) {
            pack();
        else {
            getRootPane().validate();
        if (getHeight() > MAX_HEIGHT) {
            setSize(getWidth(),MAX_HEIGHT);
    public void actionPerformed(ActionEvent ae) {
        refresh(false);
}