Java 设置本机外观时的NullPointerExcetion

因此，我试图让我的Java GUI看起来更好，因为我发现常规的GUI非常乏味：

try {
    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception e) {
    e.printStackTrace();
}

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at sun.font.FontDesignMetrics$MetricsKey.init(FontDesignMetrics.java:217)
    at sun.font.FontDesignMetrics.getMetrics(FontDesignMetrics.java:286)
    at sun.swing.SwingUtilities2.getFontMetrics(SwingUtilities2.java:1012)
    at javax.swing.JComponent.getFontMetrics(JComponent.java:1624)
    at sun.swing.MenuItemLayoutHelper.reset(MenuItemLayoutHelper.java:126)
    at javax.swing.plaf.synth.SynthMenuItemLayoutHelper.<init>(SynthMenuItemLayoutHelper.java:119)
    at javax.swing.plaf.synth.SynthGraphicsUtils.paint(SynthGraphicsUtils.java:498)
    at javax.swing.plaf.synth.SynthMenuItemUI.paint(SynthMenuItemUI.java:283)
    at javax.swing.plaf.synth.SynthMenuItemUI.update(SynthMenuItemUI.java:247)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5219)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1529)
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1452)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1249)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5167)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4978)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:808)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at sun.font.FontDesignMetrics$MetricsKey.init(FontDesignMetrics.java:217)
    at sun.font.FontDesignMetrics.getMetrics(FontDesignMetrics.java:286)
    at sun.swing.SwingUtilities2.getFontMetrics(SwingUtilities2.java:1012)
    at javax.swing.JComponent.getFontMetrics(JComponent.java:1624)
    at sun.swing.MenuItemLayoutHelper.reset(MenuItemLayoutHelper.java:126)
    at javax.swing.plaf.synth.SynthMenuItemLayoutHelper.<init>(SynthMenuItemLayoutHelper.java:119)
    at javax.swing.plaf.synth.SynthGraphicsUtils.paint(SynthGraphicsUtils.java:498)
    at javax.swing.plaf.synth.SynthMenuItemUI.paint(SynthMenuItemUI.java:283)
    at javax.swing.plaf.synth.SynthMenuItemUI.update(SynthMenuItemUI.java:247)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5219)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1529)
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1452)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1249)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5167)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4978)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:808)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

但在我运行它的第二次，我得到了以下错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at sun.font.FontDesignMetrics$MetricsKey.init(FontDesignMetrics.java:217)
    at sun.font.FontDesignMetrics.getMetrics(FontDesignMetrics.java:286)
    at sun.swing.SwingUtilities2.getFontMetrics(SwingUtilities2.java:1012)
    at javax.swing.JComponent.getFontMetrics(JComponent.java:1624)
    at sun.swing.MenuItemLayoutHelper.reset(MenuItemLayoutHelper.java:126)
    at javax.swing.plaf.synth.SynthMenuItemLayoutHelper.<init>(SynthMenuItemLayoutHelper.java:119)
    at javax.swing.plaf.synth.SynthGraphicsUtils.paint(SynthGraphicsUtils.java:498)
    at javax.swing.plaf.synth.SynthMenuItemUI.paint(SynthMenuItemUI.java:283)
    at javax.swing.plaf.synth.SynthMenuItemUI.update(SynthMenuItemUI.java:247)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5219)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1529)
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1452)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1249)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5167)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4978)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:808)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at sun.font.FontDesignMetrics$MetricsKey.init(FontDesignMetrics.java:217)
    at sun.font.FontDesignMetrics.getMetrics(FontDesignMetrics.java:286)
    at sun.swing.SwingUtilities2.getFontMetrics(SwingUtilities2.java:1012)
    at javax.swing.JComponent.getFontMetrics(JComponent.java:1624)
    at sun.swing.MenuItemLayoutHelper.reset(MenuItemLayoutHelper.java:126)
    at javax.swing.plaf.synth.SynthMenuItemLayoutHelper.<init>(SynthMenuItemLayoutHelper.java:119)
    at javax.swing.plaf.synth.SynthGraphicsUtils.paint(SynthGraphicsUtils.java:498)
    at javax.swing.plaf.synth.SynthMenuItemUI.paint(SynthMenuItemUI.java:283)
    at javax.swing.plaf.synth.SynthMenuItemUI.update(SynthMenuItemUI.java:247)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5219)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1529)
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1452)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1249)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5167)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4978)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:808)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

线程“AWT-EventQueue-0”java.lang.NullPointerException中的异常 位于sun.font.FontDesignMetrics$MetricsKey.init（FontDesignMetrics.java:217） 位于sun.font.FontDesignMetrics.getMetrics（FontDesignMetrics.java:286） 位于sun.swing.SwingUtilities2.getFontMetrics（SwingUtilities2.java:1012） 位于javax.swing.JComponent.getFontMetrics（JComponent.java:1624） 位于sun.swing.MenuItemLayoutHelper.reset（MenuItemLayoutHelper.java:126） 位于javax.swing.plaf.synth.SynthMenuItemLayoutHelper。（SynthMenuItemLayoutHelper.java:119） 位于javax.swing.plaf.synth.SynthGraphicsUtils.paint（SynthGraphicsUtils.java:498） 位于javax.swing.plaf.synth.SynthMenuItemUI.paint（SynthMenuItemUI.java:283） 位于javax.swing.plaf.synth.SynthMenuItemUI.update（SynthMenuItemUI.java:247） 位于javax.swing.JComponent.paintComponent（JComponent.java:778） 位于javax.swing.JComponent.paint（JComponent.java:1054） 位于javax.swing.JComponent.paintChildren（JComponent.java:887） 位于javax.swing.JComponent.paint（JComponent.java:1063） 位于javax.swing.JComponent.paintooffscreen（JComponent.java:5219） 在javax.swing.repaitmanager$PaintManager.paintDoubleBuffered处（repaitmanager.java:1529） 在javax.swing.repaitmanager$PaintManager.paint（repaitmanager.java:1452） 位于javax.swing.repainmanager.paint（repainmanager.java:1249） javax.swing.JComponent.\u（JComponent.java:5167） 位于javax.swing.JComponent.paintInstance（JComponent.java:4978） 在javax.swing.repaitmanager$3.run（repaitmanager.java:808） 在javax.swing.repaitmanager$3.run（repaitmanager.java:796） 位于java.security.AccessController.doPrivileged（本机方法） 位于java.security.ProtectionDomain$1.doIntersectionPrivilege（ProtectionDomain.java:76） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:796） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:769） 位于javax.swing.RepaintManager.prePaintDirtyRegions（RepaintManager.java:718） 在javax.swing.repaitmanager.access$1100（repaitmanager.java:62） 在javax.swing.repaitmanager$ProcessingRunnable.run（repaitmanager.java:1677） 在java.awt.event.InvocationEvent.dispatch（InvocationEvent.java:251）中 位于java.awt.EventQueue.dispatchEventImpl（EventQueue.java:733） 在java.awt.EventQueue.access$200（EventQueue.java:103） 位于java.awt.EventQueue$3.run（EventQueue.java:694） 在java.awt.EventQueue$3.run（EventQueue.java:692） 位于java.security.AccessController.doPrivileged（本机方法） 位于java.security.ProtectionDomain$1.doIntersectionPrivilege（ProtectionDomain.java:76） 位于java.awt.EventQueue.dispatchEvent（EventQueue.java:703） 位于java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:242） 在java.awt.EventDispatchThread.PumpeEventsforFilter（EventDispatchThread.java:161） 位于java.awt.EventDispatchThread.PumpeEventsforHierarchy（EventDispatchThread.java:150） 位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:146） 位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:138） 在java.awt.EventDispatchThread.run（EventDispatchThread.java:91） 线程“AWT-EventQueue-0”java.lang.NullPointerException中出现异常 位于sun.font.FontDesignMetrics$MetricsKey.init（FontDesignMetrics.java:217） 位于sun.font.FontDesignMetrics.getMetrics（FontDesignMetrics.java:286） 位于sun.swing.SwingUtilities2.getFontMetrics（SwingUtilities2.java:1012） 位于javax.swing.JComponent.getFontMetrics（JComponent.java:1624） 位于sun.swing.MenuItemLayoutHelper.reset（MenuItemLayoutHelper.java:126） 位于javax.swing.plaf.synth.SynthMenuItemLayoutHelper。（SynthMenuItemLayoutHelper.java:119） 位于javax.swing.plaf.synth.SynthGraphicsUtils.paint（SynthGraphicsUtils.java:498） 位于javax.swing.plaf.synth.SynthMenuItemUI.paint（SynthMenuItemUI.java:283） 位于javax.swing.plaf.synth.SynthMenuItemUI.update（SynthMenuItemUI.java:247） 位于javax.swing.JComponent.paintComponent（JComponent.java:778） 位于javax.swing.JComponent.paint（JComponent.java:1054） 位于javax.swing.JComponent.paintChildren（JComponent.java:887） 位于javax.swing.JComponent.paint（JComponent.java:1063） 位于javax.swing.JComponent.paintooffscreen（JComponent.java:5219） 在javax.swing.repaitmanager$PaintManager.paintDoubleBuffered处（repaitmanager.java:1529） 在javax.swing.repaitmanager$PaintManager.paint（repaitmanager.java:1452） 位于javax.swing.repainmanager.paint（repainmanager.java:1249） javax.swing.JComponent.\u（JComponent.java:5167） 位于javax.swing.JComponent.paintInstance（JComponent.java:4978） 在javax.swing.repaitmanager$3.run（repaitmanager.java:808） 在javax.swing.repaitmanager$3.run（repaitmanager.java:796） 位于java.security.AccessController.doPrivileged（本机方法） 位于java.security.ProtectionDomain$1.doIntersectionPrivilege（ProtectionDomain.java:76） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:796） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:769） 位于javax.swing.RepaintManager.prePaintDirtyRegions（RepaintManager.java:718） 在javax.swing.repaitmanager.access$1100（repaitmanager.java:62） 在javax.swing.repaitmanager$ProcessingRunnable.run（repaitmanager.java:1677） 在java.awt.event.InvocationEvent.dispatch（InvocationEvent.java:251）中 位于java.awt.EventQueue.dispatchEventImpl（EventQueue.java:733） 在java.awt.EventQueue.access$200（EventQueue.java:103） 位于java.awt.EventQueue$3.run（EventQueue.java:694） 在java.awt.EventQueue$3.run（EventQueue.java:692） 位于java.security.AccessController.doPrivileged（本机方法） 位于java.security.ProtectionDomain$1.doIntersectionPrivilege（ProtectionDomain.java:76） 在java.awt.Event