Java连接mysql

继上一帖子的纠正：运行结果是 SCUI Exception in thread "main" ，又是怎么回事 菜鸟谢了~
import java.sql.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.BorderLayout;
import java.awt.Rectangle;//DBCConnection.java
public   DBConnection{
Connection conn=null;
Statement stmt=null;
ResultSet rs=null;
String sql="select * from stu";
public DBConnection(){
try{
//加载驱动
Class.forName("com.mysql.jbdc.Driver").newInstance();
conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/student","root","1");//连接数据库
stmt=conn.createStatement();//创建Statement对象
}catch(Exception ex){
ex.printStackTrace();
}
}
ResultSet executeQuery(String sql){
//执行查询调用executeQuert 方法
try {
rs=stmt.executeQuery(sql);
}catch(Exception e){
}
return rs;
}
void executeUpdate(String sql){//执行其他操作调用executeUpdate 方法
try{
stmt.executeUpdate(sql);

}
catch(SQLException e){}
}
void close(){//关闭
try{
stmt.close();
conn.close();
}catch(SQLException e){}
}
}

public class SCUI extends JFrame implements ActionListener{
BorderLayout borderLayout1=new BorderLayout();
JButton jbquery=new JButton();
JButton jbinsert=new JButton();
JPanel jPanel2=new JPanel();
JLabel jLabel1=new JLabel();
JLabel jLabel2=new JLabel();
JLabel  jLabel3=new JLabel();
JTextField id=new JTextField();
JTextField name=new JTextField();
JTextField score=new JTextField();
JLabel jLabel4=new JLabel();
JLabel jLabel5=new JLabel();
JTextField sid=new JTextField();
JButton jbdelete=new JButton();
JButton jbupdate=new JButton();
JButton jbok=new JButton();
ResultSet rs=null;
JLabel ts=new JLabel();
public SCUI(){
try{
jbInit();
}catch (Exception exception){
exception.printStackTrace();
}
}
private void jbInit() throws Exception{
getContentPane().setLayout(borderLayout1);
this.setTitle("一个简单的成绩管理系统");
jPanel2.setLayout(null);
jPanel2.setBackground(Color.white);
jLabel1.setText("学号:");
jLabel1.setBounds(new Rectangle(8,103,71,30));

jLabel2.setText("成绩:");
jLabel1.setBounds(new Rectangle(6,175,42,15));
jLabel3.setText("姓名:");
jLabel3.setBounds(new Rectangle(6,144,42,15));
id.setEditable(false);
id.setBounds(new Rectangle(48,109,124,22));
name.setEditable(false);
name.setBounds(new Rectangle(48,143,124,22));
score.setEditable(false);
score.setBounds(new Rectangle(47,174,125,23));
jLabel4.setText("查询条件:");
jLabel4.setBounds(new Rectangle(4,27,86,22));
jLabel5.setText("学号:");
jLabel5.setBounds(new Rectangle(42,52,73,24));
sid.setBounds(new Rectangle (82,55,110,20));
ts.setBounds(new Rectangle(9,281,237,34));
jbinsert.setEnabled(false);
jbupdate.setEnabled(false);
jbdelete.setEnabled(false);
jbdelete.setDoubleBuffered(true);
this.getContentPane().add(jPanel2,java.awt,BorderLayout.CENTER);
jbquery.setBounds(new Rectangle(216,53,79,23));
jbinsert.setBounds(new Rectangle(20,229,72,23));
jbquery.setText("查询:");
jbquery.addActionListener(this);
    jbinsert.setText("添加::");
    jbinsert.addActionListener(this);
    jbupdate.setBounds(new Rectangle(133,230,76,23));
jbupdate.setText("修改::");
jbupdate.addActionListener(this);
jbok.setBounds(new Rectangle(217,173,79,23));
jbok.setText("编辑:");
jbok.addActionListener(this);
jbdelete.setBounds(new Rectangle(245,231,74,23));
jbdelete.setText("删除:");
jbdelete.addActionListener(this);
jPanel2.add(jLabel1);
jPanel2.add(id);
jPanel2.add(name);
jPanel2.add(score);
jPanel2.add(jLabel5);
jPanel2.add(sid);
jPanel2.add(jLabel4);
jPanel2.add(jbquery);
jPanel2.add(jbinsert);
jPanel2.add(jbok);
jPanel2.add(jLabel3);
jPanel2.add(jLabel2);
jPanel2.add(jbdelete);
jPanel2.add(jbupdate);
jPanel2.add(ts);
this.setSize(500,400);
this.setVisible(true);

}
public static void main(String args[]){
SCUI scui=new SCUI();

}
public void actionPerformed(ActionEvent e){
ts.setText("");
if(e.getSource()==jbquery){//查询
String s=sid.getText().trim();
String sql="select * from score where id'"+s+"'";
DBConnection db=new DBConnection();
rs=db.executeQuery(sql);
try{
while(rs.next()){
id.setText(rs.getString(1));
name.setText(rs.getString(2));
score.setText(rs.getString(3));
}
rs.close();
if(!id.getText().equals(""))
ts.setText("操作成功！");

}
catch(SQLException ex)
{
}
}
else if(e.getSource()==jbok){//编辑
id.setEditable(true);
name.setEditable(true);
score.setEditable(true);
jbinsert.setEnabled(true);
jbupdate.setEnabled(true);
jbdelete.setEnabled(true);


}
else if(e.getSource()==jbinsert){//添加
String s1=id.getText();
String s2=name.getText();
int s3=Integer.parseInt(score.getText());
String sql="insert into score values('"+s1+"', '"+s2+"',"+s3+")";
System.out.println(sql);
DBConnection db=DBConnection();
db.executeUpdate(sql);
ts.setText("操作成功！");

}
else if(e.getSource()==jbinsert){//修改
String s1=id.getText();
String s2=name.getText();
int s3=Integer.parseInt(score.getText());
String sql="update score set name='"+s2+"',score='"+s3+"',where id='"+s1+"'";
DBConnection db=DBConnection();
db.executeUpdate(sql);
ts.setText("操作成功！");

}
else if(e.getSource()==jbinsert){//删除
String s1=id.getText();
String s2=name.getText();
int s3=Integer.parseInt(score.getText());
String sql="delete score  where id='"+s1+"'and name='"+s2+"'and score='"+s3+"'";
DBConnection db=DBConnection();
db.executeUpdate(sql);
id.setText("");
name.setText("");
score.setText("");
id.setEditable(false);
name.setEditable(false);
score.setEditable(false);
ts.setText("操作成功！");

}

}
}