Java JMenu中的异常

我用Java开发了一个应用程序

出现的问题是，第一次单击后，如果用户再次单击菜单，则会出现以下异常

因为它显示源代码未知，所以我不可能调试它

有人能帮我吗

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at sun.font.FontDesignMetrics$MetricsKey.init(Unknown Source)
        at sun.font.FontDesignMetrics.getMetrics(Unknown Source)
        at sun.swing.SwingUtilities2.getFontMetrics(Unknown Source)
        at javax.swing.JComponent.getFontMetrics(Unknown Source)
        at sun.swing.SwingUtilities2.getFontMetrics(Unknown Source)
        at javax.swing.plaf.synth.SynthMenuItemUI.paint(Unknown Source)
        at javax.swing.plaf.synth.SynthMenuUI.paint(Unknown Source)
        at javax.swing.plaf.synth.SynthMenuUI.update(Unknown Source)
        at javax.swing.JComponent.paintComponent(Unknown Source)
        at javax.swing.JComponent.paint(Unknown Source)
        at javax.swing.JComponent.paintChildren(Unknown Source)
        at javax.swing.JComponent.paint(Unknown Source)
        at javax.swing.JComponent.paintChildren(Unknown Source)
        at javax.swing.JComponent.paint(Unknown Source)
        at javax.swing.JLayeredPane.paint(Unknown Source)
        at javax.swing.JComponent.paintChildren(Unknown Source)
        at javax.swing.JComponent.paint(Unknown Source)
        at javax.swing.JComponent.paintToOffscreen(Unknown Source)
        at javax.swing.BufferStrategyPaintManager.paint(Unknown Source)
        at javax.swing.RepaintManager.paint(Unknown Source)
        at javax.swing.JComponent._paintImmediately(Unknown Source)
        at javax.swing.JComponent.paintImmediately(Unknown Source)
        at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
        at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
        at javax.swing.RepaintManager.seqPaintDirtyRegions(Unknown Source)
        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknown Source)
        at java.awt.event.InvocationEvent.dispatch(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)

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我假设第一次单击显示菜单和菜单项。如果用户单击菜单项，您会得到一个异常，我敢打赌您没有完全实例化与菜单关联的一些菜单项组件

希望这有帮助

约翰·多纳

 at sun.font.FontDesignMetrics$MetricsKey.init(Unknown Source)

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检查字体的实例化。您需要在某个地方使用

新字体（名称，…）

。

您显示了零代码，但我可以告诉您，当您尝试遵从

null

的对象时，会发生错误。您的菜单ActionListener中的代码有问题。发布一个SSCCE（）来演示这个问题。单击菜单项上的代码调用JFileChooser并选择适当的文件名。。如果文件名不为null，则调用函数进行进一步处理。。甚至我也同意马特的观点。但我只是想弄清楚什么是空的。但是没有代码，我们只能说“好吧，祝你好运”。不。。第一次单击菜单项时，它会显示预期结果。。第二次，点击任何菜单选项抛出上述异常。。。