用线程刷新  树 的时候(调用这个方法)jtree.updateUi   会抛出一个异常  

整体代码应该没有错   
如果没使用UImanager  设置成其他ui  使用系统默认的 ui  不会报错
使用了之后 虽然会报错 但是不影响程序的运行 只是  每次刷新的时候会抛出一次 这个异常

刷新  的方法是在一个 线程中调用的

异常代码是这样：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javax.swing.plaf.synth.SynthLookAndFeel.paintRegion(SynthLookAndFeel.java:371)
        at javax.swing.plaf.synth.SynthLookAndFeel.update(SynthLookAndFeel.java:335)
        at javax.swing.plaf.synth.SynthTreeUI.update(SynthTreeUI.java:268)
        at javax.swing.JComponent.paintComponent(JComponent.java:778)
        at javax.swing.JComponent.paint(JComponent.java:1054)
        at javax.swing.JComponent.paintToOffscreen(JComponent.java:5219)
        at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
        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)

  看不懂
                  线程还没有学！