我建造了一张桌子。我想从活动窗口添加数据。但是a.getTabNum（）和其他返回的vatiables的值为 null 这是我的代码：
JButton add = new JButton();
add.setText("+");
add.setHorizontalAlignment(SwingConstants.TRAILING);
panel.add(add);
//When user clicks he can add new employee
add.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
AddEmp a = new AddEmp();
a.setSize(400,140);
a.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
a.setVisible(true);
String post = a.getPost();
String nameSurname = a.getNameSurname();
String tabNum= a.getTabNum();
Connection connect = null;
PreparedStatement statement1 = null;
try {
connect = DriverManager
.getConnection("jdbc:mysql://localhost/tabel?user=root&password=4499669");
statement1 = connect
.prepareStatement("insert into employee(tab_num, name_surname, position, id_dept) values(?, ?, ?, ?)");
int a1= Integer.parseInt(tabNum);
statement1.setInt(1, a1);
statement1.setString(2,nameSurname);
statement1.setString(3, post);
statement1.setInt(4, num);
statement1.executeUpdate();
// / List of departments
// ////////////////////////////////////////////////////////////////
} catch (Exception ex) {
ex.printStackTrace();
} finally {
try {
connect.close();
} catch (SQLException e1) {
e1.printStackTrace();
}
}
}
});
这里是ma AddEmp类：`public class AddEmp extends JFrame { private static final long serialVersionUID = 1L; JTextField a = new JTextField（30）; JTextField b = new JTextField（27）; JTextField c = new JTextField（23）; AddEmp self = this; JLabel a1 =新JLabel（“Ф.И.О”）; JLabel b1 =新JLabel（“Должность”）; JLabel c1 =新JLabel（“Табельныйномер”）; JButton o = new JButton（“OK”）;
public AddEmp(){
super("Добавление сотрудника");
setResizable(false);
JPanel p = new JPanel();
p.add(a1);
p.add(a);
p.add(b1);
p.add(b);
p.add(c1);
p.add(c);
o.setHorizontalAlignment(SwingConstants.RIGHT);
p.add(o);
getContentPane().add(p, BorderLayout.CENTER);
o.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
try{
JOptionPane.showMessageDialog(null, "Сотрудник добавлен");
self.setVisible(false);
self.dispose();
}catch(Exception e){
e.printStackTrace();
}
}
});
}
public String getPost() {
return b.getText();
}
public String getNameSurname() {
return a.getText();
}
public String getTabNum() {
return c.getText();
}
}`