我是想写一个登录界面,如现有两个界面:UserLogin和MainPage
我要在UserLogin里单击一个按钮进入MainPage界面我的代码如下:
mainFrame.setVisible(true);//mainFrame是MainPage的引用
si.closeConnection();//关闭连接
this.dispose();//消除对像
在mainFrame.setVisible(true)这一行抛了异常:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at liu.model.UserLogin.actionPerformed(UserLogin.java:112)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242
)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonL
istener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6038)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
at java.awt.Component.processEvent(Component.java:5803)
at java.awt.Container.processEvent(Container.java:2058)
at java.awt.Component.dispatchEventImpl(Component.java:4410)
at java.awt.Container.dispatchEventImpl(Container.java:2116)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322
)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
at java.awt.Container.dispatchEventImpl(Container.java:2102)
at java.awt.Window.dispatchEventImpl(Window.java:2429)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:273)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:183)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:173)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160) at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
如果那位还其他的方法,将更加感谢.
排除错误真是累啊!一个通宵没睡都没解决.
我要在UserLogin里单击一个按钮进入MainPage界面我的代码如下:
mainFrame.setVisible(true);//mainFrame是MainPage的引用
si.closeConnection();//关闭连接
this.dispose();//消除对像
在mainFrame.setVisible(true)这一行抛了异常:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at liu.model.UserLogin.actionPerformed(UserLogin.java:112)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242
)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonL
istener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6038)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
at java.awt.Component.processEvent(Component.java:5803)
at java.awt.Container.processEvent(Container.java:2058)
at java.awt.Component.dispatchEventImpl(Component.java:4410)
at java.awt.Container.dispatchEventImpl(Container.java:2116)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322
)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
at java.awt.Container.dispatchEventImpl(Container.java:2102)
at java.awt.Window.dispatchEventImpl(Window.java:2429)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:273)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:183)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:173)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160) at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
如果那位还其他的方法,将更加感谢.
排除错误真是累啊!一个通宵没睡都没解决.
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2.查询写成executeupdate
当你进行的是查询操作,当然返回值为null,所以会抛异常,查询的时候应该用execute方法。
精神可佳啊!
at liu.model.UserLogin.actionPerformed(UserLogin.java:112) 这行所指的就是下面这行mainFrame.setVisible(true);//mainFrame是MainPage的引用,即另一个界面对像的引用.
System.out.println(mainFrame);//应该是nullmainFrame.setVisible(true);