JScrollPane in a JFrame scrollbars visible but not functional no thumbtabs

Question

Here is the code that I compiled and run on J2SE v. 1.4.2 (runtime b28). I looked through the various related articles and nothing seems to help with this issue. The scrollbars appear along with the panel but the thumbtabs are not present. Any help would be appreciated.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Test {
  public static void main(String[] args){
    Test rce = new Test();
    JFrame frame = new JFrame("Test Scroll");
    JScrollPane scrollBar = new JScrollPane();
    scrollBar.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
    scrollBar.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
    Component  rcePage = rce.createComponents();
    scrollBar.getViewport().add(rcePage, null);
    frame.getContentPane().add(scrollBar, null);
    frame.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
    frame.pack();
    frame.setSize(400, 400);
    frame.setVisible(true);
  public Component createComponents() {
    JPanel pan = new JPanel();
    JLabel label = new JLabel("This is a Test!");
    pan.setBorder(BorderFactory.createEmptyBorder(
        0, //top
        0, //left
        0, //bottom
        0) //right
    pan.setLayout(null);
    label.setBounds(100, 100, 80, 20);
    pan.add(label);
    return pan;
}

Answer 1

This is a very common mistake. When you put a JPanel in a scrollpane, the scrollpane will use the panel's preferred size to determine if scrolling is needed or not. If the panel is using a LayoutManager this is generally done for you automatically. But in your case you set the layout to null, and then it is your responsibility to make sure that the getPreferredSize() method of the panel returns the correct size.
One way to fix this in the code you posted would be to override the getPreferredSize() of the panel, like so:
    public Component createComponents() {
        JPanel pan = new JPanel() {
            public Dimension getPreferredSize() {
                return getSize();
    }Then the scrollbars will appear if you make the frame smaller.
But what I really suggest is that you use a LayoutManager.