GridBagLayout 不起作用

public CheckCertificate() {
contentPanel = new JPanel();
label01 = new JLabel(Constant.CHECK_CERTIFICATE_WIN_LABEL_01);
label02 = new JLabel(Constant.CHECK_CERTIFICATE_WIN_LABEL_02);
textField01 = new JTextField();
textField02 = new JTextField();
button01 = new JButton(Constant.CHECK_CERTIFICATE_WIN_BUTTON_01);
button02 = new JButton(Constant.CHECK_CERTIFICATE_WIN_BUTTON_02);
//窗口默认大小
     this.setSize(WIDTH,HEIGHT);    
     //获取屏幕大小
        Dimension screenSize =Toolkit.getDefaultToolkit().getScreenSize();
        //窗口居中显示
        this.setLocation(screenSize.width/2 - this.WIDTH/2, screenSize.height/2 - this.HEIGHT/2);
    //窗口关闭时后台程序关闭
    this.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
    //窗口标题
    this.setTitle("核对证件");
    
    GridBagLayout gbl = new GridBagLayout();  
    GridBagConstraints gbs = new GridBagConstraints();  
    contentPanel.setLayout(gbl);
    contentPanel.add(button01);contentPanel.add(button02);     
    
gbs.fill=GridBagConstraints.BOTH;gbs.gridwidth=4;gbs.gridheight=1;  
gbs.insets = new Insets(5, 5, 5, 5);
gbs.weightx=0;gbs.weighty=0;  
    gbs.gridx=0;gbs.gridy=0;  
    gbl.setConstraints(button01, gbs);
    
    gbs.fill=GridBagConstraints.BOTH;gbs.gridwidth=1;gbs.gridheight=1;  
    gbs.weightx=0;gbs.weighty=0;  
    gbs.gridx=4;gbs.gridy=0;
    gbl.setConstraints(button02, gbs);
    
    
    this.setContentPane(contentPanel);     
    this.setVisible(true);
}