Java连接数据库的奇怪问题！急！！

拿Access建个表，点确定时，不显示数据，但是拖动一下滚动条或点击表格时，数据才显示，这是什么原因呢？
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
class ResultWin extends JFrame implements ActionListener{
  Object a[][];
  Object columnName[]={"学号","姓名","出生日期","数学","物理","英语"};
  JTable table;
  JButton btn;
  Container cont;
  int number1,maths1,phy1,english1;
  Date brith1;
  String name1;
  Connection conn=null;
  Statement  stmt=null;
  ResultSet rs=null;
  JProgressBar p_bar;
  
  public ResultWin(){
    super("数据查询");
    a=new Object[30][6];
    table=new JTable(a,columnName);
    setSize(300,300);
    setVisible(true);
    btn=new JButton("确定");
    
    addWindowListener(new WindowAdapter(){
      public void windowClosing(WindowEvent e){
       System.exit(0);
      }
    });
    
    btn.addActionListener(this);
    
    p_bar=new JProgressBar(JProgressBar.VERTICAL,0,50);
    p_bar.setStringPainted(true);
    
    cont=getContentPane();
    cont.add(btn,BorderLayout.SOUTH);
    cont.add(new JScrollPane(table),BorderLayout.CENTER);
    cont.add(p_bar,BorderLayout.WEST);    
  }
  public void actionPerformed(ActionEvent e){
    if(e.getSource()==btn){
     int i=0;
     try
     {
     Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
     }
     catch(ClassNotFoundException ee){
 }
     try{
       conn=DriverManager.getConnection("jdbc:odbc:ttt","","");
       stmt=conn.createStatement();
       rs=stmt.executeQuery("select * from chengjibiao");
       while(rs.next()){
        number1=rs.getInt(1);
        name1=rs.getString(2);
        brith1=rs.getDate(3);
        maths1=rs.getInt(4);
        phy1=rs.getInt(5);
        english1=rs.getInt(6);
        a[i][0]=String.valueOf(number1);
        a[i][1]=name1;
        a[i][2]=brith1;
        a[i][3]=String.valueOf(maths1);
        a[i][4]=String.valueOf(phy1);
        a[i][5]=String.valueOf(english1);
        i++;       
        p_bar.setValue(10*i);
        p_bar.setString("查询了"+i+"条记录");       
        }
        conn.close();
     }
     catch(SQLException e1){
 }
    }
  }  
}
public class JTableSQLExam{
  public static void main(String args[]){
    ResultWin win=new ResultWin();
    win.pack();
  }
}