java button控制数据更新database 问题, 急~~

wyewh

小弟在写一个类似pos system 的java 小程式
可是遇到一个很怪的问题，尝试了很久还是无法解决
问题是这样的，当我要按个button 来把输入的数据update 进 mysql database 时，就会出现exception
其中一小段 ：jdbc, connection的一些code 在其他地方写了
private void jButton31ActionPerformed(ActionEvent evt) {
        System.out.println("jButton31.actionPerformed, event=" + evt);

         jComboBox1.addItem(jTextField1.getText());        
            try {
                jTextField1.setText(null);
                stmt = con.createStatement();
                stmt.executeUpdate(sql1);
                stmt.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        
            System.out.println(" rows were inserted ";
        }
    }
结果出现 ：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at As.Menu.jButton31ActionPerformed(Menu.java:314)
    at As.Menu.access$5(Menu.java:301)
    at As.Menu$6.actionPerformed(Menu.java:270)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.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.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(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)

问题只有当存在这个eventperform 里面，如果我把     stmt = con.createStatement(); 和相关的几行去掉就没有问题。。。可是也就不能update 我的数据

我在网上找到一个跟我极相识的问题 http://www.experts-exchange.com/ ... ava/Q_21746419.html
各位高手如果知道问题所在请帮忙，因为真的很急
万分感谢~~！！！！

[ 本帖最后由 wyewh 于 17-3-2009 08:03 AM 编辑 ]

extremeJ

你的 nullpointerexception 是在这里的 code  的第几行?