用swing mysql 写了一个QQ登录界面,但是功能实现不了，不能注册用户和登录验证解决思路

package com.MyQQ.test;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

/**
 * @author 
 * 2012-4-4
 */
public class QQFrame    extends  JFrame {
    String  str1=null;  
    String  str2=null;
    
    JLabel  label1=new JLabel("用户名:");
    JLabel  label2=new JLabel("密     码:");
    JTextField  tf1=new JTextField(10);
    JTextField  tf2=new JTextField(10);

    JButton  bt1=new JButton("登陆");
    JButton  bt2=new JButton("取消");
    JButton  bt3=new JButton("注册");
    public QQFrame() {
        init();
        
    }
    
public void  init(){
    this.setTitle("QQVersion 0.1");

    this.setBounds(200, 200, DEFULAT_WIDTH,DEFULAT_HEIGHT);
    
    bt1.addActionListener(new ActionListener() {
        
        public void actionPerformed(ActionEvent e) {
            str1=tf1.getText();
            str2=tf2.getText();
            new QQDB().check(str1, str2);
            tf1.setText("");
            tf2.setText("");
        }
    });
    bt2.addActionListener(new ActionListener() {
        
        @Override
        public void actionPerformed(ActionEvent e) {
            System.exit(0);
        }
    });
    bt3.addActionListener(new  ActionListener() {
        
        @Override
        public void actionPerformed(ActionEvent e) {
            str1=tf1.getText();
            str2=tf2.getText();
            new  QQDB().addAccount(str1, str2);
            
            tf1.setText("");
            tf2.setText("");
        }
    });
    
    
    
    JPanel  p1=new JPanel();
    JPanel  p2=new JPanel();
    JPanel  p3=new JPanel();
    p1.add(label1);
    p1.add(tf1);
    p2.add(label2);
    p2.add(tf2);
    p3.add(bt1);
    p3.add(bt2);
    p3.add(bt3);
    
    
    
    this.setLayout(new  GridLayout(3,1));
    this.add(p1);
    this.add(p2);
    this.add(p3);
    
    this.pack();
    
}
    
    public static void main(String[] args) {
        
        EventQueue.invokeLater(new Runnable() {
            
            @Override
            public void run() {
                
            JFrame   frame=new  QQFrame();
            frame.setVisible(true);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            }
        });

    }
    private  static  final int DEFULAT_WIDTH=150;
    
    private  static  final  int DEFULAT_HEIGHT=80;

}









package com.MyQQ.test;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

/**
 * @author 
 *2012-4-4
 */
public class QQDB {
    Connection conn=null;
    PreparedStatement  ps=null;
    ResultSet   res=null;
    
    String  str1=null;
    String  str2=null;
    
    String   url="jdbc:mysql://localhost:3306/pwd?user=root&password=root";
    public  QQDB(){
        init();
    }
    public void init(){
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn=DriverManager.getConnection(url);
            System.out.println("连接成功");
            
        } catch (Exception e) {
           e.printStackTrace();
        }
    }
    //把从文本框里面取的值传进来和数据库里面的对比
    public void check(String  st1,String  st2){
        this.str1=st1; this.str2=st2;
        
        try {
            String  sql="select  userPwd  from  pwd  where userName=str1";
            ps=conn.prepareStatement(sql);
            ps.execute();
            res=ps.executeQuery();
            if (ps.execute()) {
                System.out.println("有此帐户 ");
                
                if(str2.equals(res.getString("userPwd"))){
                    System.out.println("密码正确");
                }else  {
                    System.out.println("密码不正确");
                }
            }
            conn.close();
            ps.close();
            res.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        
    }
    public  void  addAccount(String  st3,String  st4){
        try {
            String  sql2="insert into  pwd(userName,userPwd) values(st3,st4)";
            ps=conn.prepareStatement(sql2);
            ps.executeUpdate();
            System.out.println("注册成功");
            
        } catch (Exception e) {
             e.printStackTrace();
        }
    }

}