title: GroupLayout can only be used with one container at a time
body: <p>Not sure why this error is coming up. I am using GroupLayout because I want it to do the spacing for me and will be adding more panels to the frame in the future. Below is the stack trace.</p>
  
  <pre><code>Exception in thread "main" java.lang.IllegalArgumentException: GroupLayout can only be used with one Container at a time
      at javax.swing.GroupLayout.checkParent(Unknown Source)
      at javax.swing.GroupLayout.invalidateLayout(Unknown Source)
      at java.awt.Container.invalidate(Unknown Source)
      at java.awt.Component.addNotify(Unknown Source)
      at java.awt.Container.addNotify(Unknown Source)
      at javax.swing.JComponent.addNotify(Unknown Source)
      at java.awt.Container.addNotify(Unknown Source)
      at javax.swing.JComponent.addNotify(Unknown Source)
      at java.awt.Container.addNotify(Unknown Source)
      at javax.swing.JComponent.addNotify(Unknown Source)
      at javax.swing.JRootPane.addNotify(Unknown Source)
      at java.awt.Container.addNotify(Unknown Source)
      at java.awt.Window.addNotify(Unknown Source)
      at java.awt.Frame.addNotify(Unknown Source)
      at java.awt.Window.pack(Unknown Source)
      at client.AlternateGUI.drawGui(AlternateGUI.java:54)
      at client.AlternateGUI.main(AlternateGUI.java:24)
  </code></pre>
  
  <p>Here is the code:</p>
  
  <pre><code>package client;
  
  import java.awt.Component;*
  
  public class AlternateGUI {
      private JList people;
      private DefaultListModel dlm;
      private JLabel l1, l2, l3;
      private JFrame alternateGUIFrame;
      private final static ImageIcon unavailableIcon = new ImageIcon("offline.png");
  
      public static void main(String[] args)
      {
          AlternateGUI ls = new AlternateGUI();
          ls.drawGui();
      }
  
      public AlternateGUI(){
          dlm = new DefaultListModel();
          people = new JList(dlm);
  
          alternateGUIFrame = new JFrame();
  
          JScrollPane peopleScroller = new JScrollPane(people, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
          people.setCellRenderer(new CellRenderer());
  
          GroupLayout alternateGUILayout = new GroupLayout(alternateGUIFrame);
          alternateGUIFrame.setLayout(alternateGUILayout);
  
          alternateGUILayout.setAutoCreateGaps(true);
          alternateGUILayout.setAutoCreateContainerGaps(true);
          alternateGUILayout.setHorizontalGroup(alternateGUILayout.createSequentialGroup()
                  .addComponent(peopleScroller));
          alternateGUILayout.setVerticalGroup(alternateGUILayout.createSequentialGroup()
                  .addComponent(peopleScroller));
          }
  
      public void drawGui() {
          l1 = new JLabel("Hi", unavailableIcon , JLabel.LEFT);
          l2 = new JLabel("Hello", unavailableIcon , JLabel.LEFT);
          l3 = new JLabel("Bye", unavailableIcon , JLabel.LEFT);
          dlm.addElement(l1);
          dlm.addElement(l2);
          dlm.addElement(l3);
  
          alternateGUIFrame.pack();
          alternateGUIFrame.setVisible(true);
      }
  
      class CellRenderer implements ListCellRenderer
      {
          public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus)
          {
              Component com = (Component)value;
              return com;
          }
      }
  }
  </code></pre>