添加选项卡替换选项卡（Java）

我是Java的新手，需要一点帮助。话虽这么说，我肯定我的代码是草率的。我将NetBeans用于GUI生成器，并且正在学习此过程中的技巧。我在这里有一个SSCC，但是因为即时通讯使用NetBeans相当长。

public class tabtest extends javax.swing.JFrame {

public tabtest() {
    initComponents();
}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    addTabDialog = new javax.swing.JDialog();
    titleTextBox = new javax.swing.JTextField();
    jLabel1 = new javax.swing.JLabel();
    addTabConfirmButton = new javax.swing.JButton();
    jLabel2 = new javax.swing.JLabel();
    tabPane = new javax.swing.JTabbedPane();
    addTabButton = new javax.swing.JButton();

    addTabDialog.setBounds(new java.awt.Rectangle(0, 0, 400, 400));

    titleTextBox.setText("New Tab");

    jLabel1.setText("Tab Title");

    addTabConfirmButton.setText("Confirm");
    addTabConfirmButton.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            addTabConfirmButtonActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout addTabDialogLayout = new javax.swing.GroupLayout(addTabDialog.getContentPane());
    addTabDialog.getContentPane().setLayout(addTabDialogLayout);
    addTabDialogLayout.setHorizontalGroup(
        addTabDialogLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(addTabDialogLayout.createSequentialGroup()
            .addGap(23, 23, 23)
            .addComponent(jLabel1)
            .addGap(18, 18, 18)
            .addGroup(addTabDialogLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(addTabConfirmButton)
                .addComponent(titleTextBox, javax.swing.GroupLayout.PREFERRED_SIZE, 96, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addContainerGap(211, Short.MAX_VALUE))
    );
    addTabDialogLayout.setVerticalGroup(
        addTabDialogLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(addTabDialogLayout.createSequentialGroup()
            .addGap(77, 77, 77)
            .addGroup(addTabDialogLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(titleTextBox, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(jLabel1))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 196, Short.MAX_VALUE)
            .addComponent(addTabConfirmButton)
            .addGap(84, 84, 84))
    );

    jLabel2.setText("This is a new Tab");

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    addTabButton.setText("add new tab");
    addTabButton.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            addTabButtonActionPerformed(evt);
        }
    });
    tabPane.addTab("+", addTabButton);

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(40, 40, 40)
            .addComponent(tabPane, javax.swing.GroupLayout.PREFERRED_SIZE, 326, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(34, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(89, 89, 89)
            .addComponent(tabPane, javax.swing.GroupLayout.PREFERRED_SIZE, 178, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(33, Short.MAX_VALUE))
    );

    pack();
}// </editor-fold>                        

private void addTabButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
    addTabDialog.setLocationRelativeTo(null);
    addTabDialog.setVisible(true);
}                                            

private void addTabConfirmButtonActionPerformed(java.awt.event.ActionEvent evt) {                                                    

    tabPane.addTab(titleTextBox.getText(),jLabel2);
    tabPane.setSelectedIndex(tabPane.getTabCount()-1);
    addTabDialog.setVisible(false);

}                                                   

public static void main(String args[]) {
   java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new tabtest().setVisible(true);
        }
    });
}
// Variables declaration - do not modify                     
private javax.swing.JButton addTabButton;
private javax.swing.JButton addTabConfirmButton;
private javax.swing.JDialog addTabDialog;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JTabbedPane tabPane;
private javax.swing.JTextField titleTextBox;
// End of variables declaration                   

我需要帮助的主要部分是这一部分，其余的只是构建GUI

private void addTabButtonActionPerformed(java.awt.event.ActionEvent evt){                                             
    addTabDialog.setLocationRelativeTo(null);
    addTabDialog.setVisible(true);
}                                            

private void addTabConfirmButtonActionPerformed(java.awt.event.ActionEvent evt){                                                    

    tabPane.addTab(titleTextBox.getText(),jLabel2);
    tabPane.setSelectedIndex(tabPane.getTabCount()-1);
    addTabDialog.setVisible(false);

}

抱歉，代码难免...无论如何，如果运行此代码，您将看到在尝试添加2个选项卡后，第二个选项卡将替换您尝试添加的第一个选项卡。我究竟做错了什么？我敢肯定它很简单，但是任何帮助将不胜感激！谢谢你！