所以我尝试使我的Java GUI看起来更好，因为我发现常规的这个非常沉闷：
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception e) {
e.printStackTrace();
}
但是第二次我运行它我得到了这些错误：
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)
但如果我删除LAF代码一切正常。有什么问题？我是一个使用GUI的新手，因为我更像是一个编程爱好者，而不是一个设计。