组布局一次只能与一个容器一起使用

不知道为什么会出现此错误。我正在使用GroupLayout，因为我希望它为我做间距，并将来会向框架添加更多面板。下面是堆栈跟踪。

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)

代码如下：

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;
        }
    }
}