SpringLayout completely wrong

Question

I've built several SpringLayout GUI apps over the years, but suddenly I can't get the simplest configuration to work. I must be missing something basic, but whatever it is escapes me. For my test case, I just want to have two JPanels, each of them the full width of the contentPane. The bottom one should be a fixed height (100), anchored to the bottom of the contentPane, and the top one should be anchored to the top of the contentPane for its top edge and the top of the bottom panel for its bottom edge.
My code is given below. The panels are white and gray, so you can see where they end up. Nothing is as specified. The widths are wrong, the placement is wrong, and at least the height of the top panel is wrong. Can someone pelase tell me what I'm missing?
package net.midnightjava.test;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import javax.swing.JDialog;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Spring;
import javax.swing.SpringLayout;
import javax.swing.SwingUtilities;
public class SpringLayoutTest extends JDialog{
     public static void main(String[] args){
          new SpringLayoutTest();
     public SpringLayoutTest(){
          SwingUtilities.invokeLater(new Runnable(){
               public void run(){
                    createAndShowGUI();
     private void createAndShowGUI(){
          int width = 600;
          int height =500;
          Container mainPane = getContentPane();
          SpringLayout sl = new SpringLayout();
          SpringLayout.Constraints cons;
          JPanel topPanel = new JPanel();
          topPanel.setBackground(Color.WHITE);
          JLabel topLabel = new JLabel("This is the top panel");
          topPanel.add(topLabel);
          JPanel bottomPanel = new JPanel();
          bottomPanel.setBackground(Color.GRAY);
          JLabel bottomLabel = new JLabel("This is the bottom label");
          bottomPanel.add(bottomLabel);
          mainPane.setSize(new Dimension(width, height));
          mainPane.setLayout(sl);
          mainPane.add(topPanel);
          mainPane.add(bottomPanel);
          cons = new SpringLayout.Constraints();
          cons.setY(Spring.constant(5));
          sl.putConstraint(SpringLayout.EAST, topPanel, -5, SpringLayout.EAST,
                    mainPane);
          sl.putConstraint(SpringLayout.WEST, topPanel, 5, SpringLayout.WEST,
                    mainPane);
          sl.putConstraint(SpringLayout.SOUTH, topPanel, -5, SpringLayout.NORTH,
                    bottomPanel);
          sl.addLayoutComponent(topPanel, cons);
          cons = new SpringLayout.Constraints();
          sl.putConstraint(SpringLayout.EAST, bottomPanel, -5, SpringLayout.EAST,
                    mainPane);
          sl.putConstraint(SpringLayout.WEST, bottomPanel, 5, SpringLayout.WEST,
                    mainPane);
          sl.putConstraint(SpringLayout.SOUTH, bottomPanel, -5, SpringLayout.SOUTH,
                    mainPane);
          cons.setHeight(Spring.constant(100));
          sl.addLayoutComponent(bottomPanel, cons);
          setSize(new Dimension(width, height));
          setLocationRelativeTo(null);
          setVisible(true);
}

Answer 1

You mentioned the brittleness of my constructor, but I think you forgot to apply your solution.Huh? The code I posted doesn't even have an explicit constructor. From main, construction is completed before createAndShowGUI is called. And setVisible is in createAndShowGUI.
About order of sequencing setConstraints calls, I really don't know, but logically it shouldn't be a criterion. Before today, I hadn't even taken a look at the SpringLayout API. I'm not a developer, just a hobby programmer, and dive into questions that interest me. Yours did.
As far as your layout is concerned, I would rather handle it by setting the sizes of the bottom panel, but that's just me. Also, since the class doesn't add any functionality to JDialog, I would use aggregation rather than inheritance, and that's not just me, it's acceptedly better, as the class can then expose only required functionality and not unnecessarily expose the complexity of a JDialog.import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import javax.swing.JDialog;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SpringLayout;
import javax.swing.SwingUtilities;
public class SpringLayoutTest2 {
   JDialog dialog;
   private void createAndShowGUI(){
      int width = 600;
      int height =500;
      JPanel topPanel = new JPanel();
      topPanel.setBackground(Color.WHITE);
      JLabel topLabel = new JLabel("This is the top panel");
      topPanel.add(topLabel);
      System.out.println(topPanel.getPreferredSize());
      JPanel bottomPanel = new JPanel();
      bottomPanel.setBackground(Color.GRAY);
      // freeze the height
      Dimension size = new Dimension(Integer.MAX_VALUE, 100);
      bottomPanel.setMaximumSize(size);
      bottomPanel.setPreferredSize(size);
      bottomPanel.setMinimumSize(size);
      JLabel bottomLabel = new JLabel("This is the bottom label");
      bottomPanel.add(bottomLabel);
      dialog = new JDialog();
      Container contentPane = dialog.getContentPane();
      SpringLayout layout = new SpringLayout();
      contentPane.setLayout(layout);
      contentPane.add(topPanel);
      contentPane.add(bottomPanel);
      // layout for topPanel
      layout.putConstraint(SpringLayout.WEST, topPanel,
            5, SpringLayout.WEST, contentPane);
      layout.putConstraint(SpringLayout.NORTH, topPanel,
            5, SpringLayout.NORTH, contentPane);
      layout.putConstraint(SpringLayout.EAST, contentPane,
            5, SpringLayout.EAST, topPanel);
      // layout for bottomPanel
      layout.putConstraint(SpringLayout.WEST, bottomPanel,
            0, SpringLayout.WEST, topPanel);
      layout.putConstraint(SpringLayout.NORTH, bottomPanel,
            5, SpringLayout.SOUTH, topPanel);
      layout.putConstraint(SpringLayout.EAST, topPanel,
            0, SpringLayout.EAST, bottomPanel);
      layout.putConstraint(SpringLayout.SOUTH, contentPane,
            5, SpringLayout.SOUTH, bottomPanel);
      dialog.setSize(new Dimension(width, height));
      dialog.setLocationRelativeTo(null);
      dialog.setModal(true);
      dialog.setVisible(true);
      System.exit(0);
   public static void main(String[] args){
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            new SpringLayoutTest2().createAndShowGUI();
}db