为什么JCombox总是报错？

Question

                if(e.getSource()==list3)
{  
list1.removeAllItems();
name=(String)list3.getSelectedItem();  
String s2;
Statement sql;
                Connection con=null;
                String str2;
        ResultSet rs=null;   
      try 
                            {
                                  try
                                {  
                                 Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver").newInstance();
        }
       catch(IllegalAccessException e0){System.out.println("OK,成功连接到数据库");}
       catch(InstantiationException e2){System.out.println("no,成功连接到数据库");}
                               String url="jdbc:microsoft:sqlserver://QPSERVER:1433;DatabaseName=UFDATA_001_2007";
      String usern="sa";
      String passw="156078";
      con=DriverManager.getConnection(url,usern,passw); 
      System.out.println("OK,成功连接到数据库");
    }  catch(ClassNotFoundException classnotfound) {  System.out.println("OK"); }
       catch(SQLException s) { s.printStackTrace();}
          
           try
                {    
                      sql=con.createStatement();
                  str2="select name from sysobjects where type='u' ";
                  rs=sql.executeQuery(str2);
                              
                while(rs.next())
                            {  
                    s2=rs.getString(1);    
                    list1.addItem(s2);     
                             }
                            rs.close();
                            sql.close();
                            con.close();
                }
          catch(Exception ex)     {  ex.printStackTrace();  }
          
     
}
报错：
OK
java.lang.NullPointerException
at fram.itemStateChanged(fram.java:258)
at javax.swing.JComboBox.fireItemStateChanged(Unknown Source)
at javax.swing.JComboBox.selectedItemChanged(Unknown Source)
at javax.swing.JComboBox.contentsChanged(Unknown Source)
at javax.swing.AbstractListModel.fireContentsChanged(Unknown Source)
at javax.swing.DefaultComboBoxModel.setSelectedItem(Unknown Source)
at javax.swing.JComboBox.setSelectedItem(Unknown Source)
at javax.swing.JComboBox.setSelectedIndex(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup$Handler.mouseReleased(Unknown Source)
at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup$1.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)高人救我啊！

Answer 1

list1 是不是有加監聽噢 ？while(rs.next()) 
                            {  
                s2=rs.getString(1); 
                  list1.removeItemListener(你的listener);
                  list1.addItem(s2);
                  list1.addItemListener(你的listener);    
                            } 試試這樣呢？

Answer 2

list1有监听，但是item没有监听，我以前用桥连接好用的，改用数据库驱动做的话，就出问题了