import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Myframe extends JFrame
{
   public Myframe()
   {
    super("Find");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //String laf = UIManager.getCrossPlatformLookAndFeelClassName();
    String laf = UIManager.getSystemLookAndFeelClassName();
    try {
         UIManager.setLookAndFeel(laf);
    } catch (UnsupportedLookAndFeelException exc) {
     System.err.println("Warning: UnsupportedLookAndFeel: " + laf);
    } catch (Exception exc) {
     System.err.println("Error loading " + laf + ": " + exc);
    }
  
   JLabel label1 = new JLabel("用户名");
   JLabel label2 = new JLabel("密码");
   JTextField textField1 = new JTextField();
   JTextField textField2 = new JTextField();
   JCheckBox teacherCheckBox = new JCheckBox("教师");
   JCheckBox studentCheckBox = new JCheckBox("学生");
   JButton dengluButton = new JButton("登录");
   JButton cancelButton = new JButton("退出");
   
   
   Container c = getContentPane();
   GroupLayout layout = new GroupLayout(c);
   c.setLayout(layout);
   
   //自动设定组件、组之间的间隙
   layout.setAutoCreateGaps(true);
   layout.setAutoCreateContainerGaps(true);
   //LEADING -- 左对齐    BASELINE -- 底部对齐 CENTER -- 中心对齐
   GroupLayout.ParallelGroup hpg1 = layout.createParallelGroup(GroupLayout.Alignment.LEADING);
   hpg1.addComponent(label1);
   hpg1.addComponent(label2);
   
   GroupLayout.ParallelGroup hpg2 = layout.createParallelGroup(GroupLayout.Alignment.LEADING);
   hpg2.addComponent(textField1);
   hpg2.addComponent(textField2);
   
   GroupLayout.ParallelGroup hpg3 = layout.createParallelGroup(GroupLayout.Alignment.LEADING);
   hpg3.addComponent(teacherCheckBox);
   hpg3.addComponent(dengluButton);
   
   GroupLayout.ParallelGroup hpg4 = layout.createParallelGroup(GroupLayout.Alignment.LEADING);
   hpg4.addComponent(studentCheckBox);
   hpg4.addComponent(cancelButton);
   
   GroupLayout.SequentialGroup hpg5 = layout.createSequentialGroup();
   hpg5.addGroup(hpg3).addGroup(hpg4);
   
   GroupLayout.ParallelGroup hpg6 = layout.createParallelGroup(GroupLayout.Alignment.LEADING);
   hpg6.addGroup(hpg2);
   hpg6.addGroup(hpg5);
   
   //水平
   layout.setHorizontalGroup(layout.createSequentialGroup()
            .addGroup(hpg1).addGroup(hpg6));   
   
 //设定两个Button在水平方向一样宽
   layout.linkSize(SwingConstants.HORIZONTAL,new Component[] { dengluButton, cancelButton });
   //layout.linkSize(SwingConstants.HORIZONTAL,new Component[] {teacherCheckBox,studentCheckBox });
   
   GroupLayout.ParallelGroup vpg1 = layout.createParallelGroup(GroupLayout.Alignment.BASELINE);
   vpg1.addGroup(hpg1);
   vpg1.addGroup(hpg2);
   
 //垂直
   layout.setVerticalGroup(layout.createSequentialGroup()
        .addGroup(vpg1).addGroup(hpg5));
   
   setLocation(200,200);
   pack();
   setVisible(true);

   }
   public static void main(String[] args)
   {
      new Myframe();
   }
}
错误提示：
Exception in thread "main" java.lang.IllegalStateException: javax.swing.JTextField[,0,0,0x0,invalid,layout=javax.swing.plaf.basic.BasicTextUI$UpdateHandler,alignmentX=0.0,alignmentY=0.0,border=com.sun.java.swing.plaf.windows.XPStyle$XPFillBorder@16ee3ec,flags=296,maximumSize=,minimumSize=,preferredSize=,caretColor=javax.swing.plaf.ColorUIResource[r=0,g=0,b=0],disabledTextColor=javax.swing.plaf.ColorUIResource[r=172,g=168,b=153],editable=true,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],selectedTextColor=javax.swing.plaf.ColorUIResource[r=255,g=255,b=255],selectionColor=javax.swing.plaf.ColorUIResource[r=49,g=106,b=197],columns=0,columnWidth=0,command=,horizontalAlignment=LEADING] is not attached to a vertical group
    at javax.swing.GroupLayout.checkComponents(Unknown Source)
    at javax.swing.GroupLayout.prepare(Unknown Source)
    at javax.swing.GroupLayout.preferredLayoutSize(Unknown Source)
    at java.awt.Container.preferredSize(Unknown Source)
    at java.awt.Container.getPreferredSize(Unknown Source)
    at javax.swing.JComponent.getPreferredSize(Unknown Source)
    at javax.swing.JRootPane$RootLayout.preferredLayoutSize(Unknown Source)
    at java.awt.Container.preferredSize(Unknown Source)
    at java.awt.Container.getPreferredSize(Unknown Source)
    at javax.swing.JComponent.getPreferredSize(Unknown Source)
    at java.awt.BorderLayout.preferredLayoutSize(Unknown Source)
    at java.awt.Container.preferredSize(Unknown Source)
    at java.awt.Container.getPreferredSize(Unknown Source)
    at java.awt.Window.pack(Unknown Source)
    at Myframe.<init>(Myframe.java:79)
    at Myframe.main(Myframe.java:85)