请教一个关于向数据库添加数据的问题


import java.sql.*;
import javax.swing.*;
import java.awt.event.*;/**
 *
 * @author FC
 */
public class Applicant extends JFrame{
    JPanel panel=new JPanel();
    JLabel label1=new JLabel("ID");
    JLabel label2=new JLabel("Name");
    JLabel label3=new JLabel("Address");
    JLabel label4=new JLabel("Position");
    private JTextField textID=new JTextField(8);
    private JTextField textName=new JTextField(8);
    private JTextField textAddress=new JTextField(30); 
    String position[]={"市场部经理","市场咨询人员","会计"};
    JComboBox box=new JComboBox(position);
    private JButton buttonSubmit=new JButton("提交");
    private JButton buttonReset=new JButton("重置");
    String driver="sun.jdbc.odbc.JdbcOdbcDriver";
    String url="jdbc:odbc:con_java";
    String user="sa";
    String password="hanjian";
    String recid=this.textID.getText();
    String recname=this.textName.getText();
    String recaddress=this.textAddress.getText();
    String recposition=(String)box.getSelectedItem();
    /** Creates a new instance of Applicant */
    public Applicant() {
        this.getContentPane().add(panel);
        panel.add(label1);
panel.add(textID);
panel.add(label2);
panel.add(textName);
panel.add(label3);
panel.add(textAddress);
panel.add(label4);
panel.add(box);
panel.add(buttonReset);
panel.add(buttonSubmit);
        ActionListener a=new MyAction();
        buttonSubmit.addActionListener(a);
        buttonReset.addActionListener(new MyAction());
        setSize(400, 400);
        setVisible(true);
        setDefaultCloseOperation(3);
    }
    class MyAction implements ActionListener{
        public void actionPerformed(ActionEvent e){
            Object obj=e.getSource();
            if(obj==buttonSubmit){
                if(textID.getText().length()==0){
                        JOptionPane.showMessageDialog(null,"ID不能为空");
                }
                else if (textName.getText().length()==0){
                        JOptionPane.showMessageDialog(null ,"姓名不能为空");
                }
                 else if (textAddress.getText().length()==0){
                        JOptionPane.showMessageDialog(null,"地址不能为空");
                 }
               
                try{
                    Class.forName(driver);
                    Connection conn=DriverManager.getConnection(url,user,password);
                    String sql="insert into Applicant values(?,?,?,?)";
                    PreparedStatement ps=conn.prepareStatement(sql,ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);
                    String recid=textID.getText();
                    String recname=textName.getText();
                    String recaddress=textAddress.getText();
                    String recposition=(String)box.getSelectedItem();
                    ps.setString(1, recid);
                    ps.setString(2, recname);
                    ps.setString(3, recaddress);
                    ps.setString(4,recposition);
为什么这段注释代码必须放在ps.setString()之前呢，若放在setString()后面就没法往数据库中添加数据了，请问这是怎么回事？多谢       
                 /* String recid=textID.getText();
                    String recname=textName.getText();
                    String recaddress=textAddress.getText();
                    String recposition=(String)box.getSelectedItem();*/
                   
                    
                    ps.executeUpdate();
      
        
                    
                    JOptionPane.showMessageDialog(null ,"信息添加成功");
                }
                catch(Exception a){
                    System.out.println("error"+a);
                }
            }   
            if(obj==buttonReset){
                textID.setText("");
                textAddress.setText("");
                textName.setText("");
            }           
            
        
        }
        
    }
    public static void main(String args[]){
        new Applicant();
    }
    
}