有没有人知道我如何在Java Swing中开始调试这个错误?
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.BoxLayout.preferredLayoutSize(BoxLayout.java:282)
at java.awt.Container.preferredSize(Container.java:1599)
at java.awt.Container.getPreferredSize(Container.java:1584)
at javax.swing.JComponent.getPreferredSize(JComponent.java:1636)
at java.awt.BorderLayout.layoutContainer(BorderLayout.java:804)
at java.awt.Container.layout(Container.java:1421)
at java.awt.Container.doLayout(Container.java:1410)
at java.awt.Container.validateTree(Container.java:1507)
at java.awt.Container.validateTree(Container.java:1513)
at java.awt.Container.validate(Container.java:1480)
at javax.swing.plaf.basic.BasicTabbedPaneUI.ensureCurrentLayout(BasicTabbedPaneUI.java:1429)
at javax.swing.plaf.basic.BasicTabbedPaneUI.getTabBounds(BasicTabbedPaneUI.java:1449)
at javax.swing.plaf.synth.SynthTabbedPaneUI.setRolloverTab(SynthTabbedPaneUI.java:491)
at javax.swing.plaf.basic.BasicTabbedPaneUI$TabbedPaneLayout.layoutContainer(BasicTabbedPaneUI.java:2384)
at java.awt.Container.layout(Container.java:1421)
at java.awt.Container.doLayout(Container.java:1410)
at java.awt.Container.validateTree(Container.java:1507)
at java.awt.Container.validate(Container.java:1480)
at javax.swing.plaf.basic.BasicTabbedPaneUI.ensureCurrentLayout(BasicTabbedPaneUI.java:1429)
at javax.swing.plaf.basic.BasicTabbedPaneUI.getTabBounds(BasicTabbedPaneUI.java:1449)
at javax.swing.plaf.synth.SynthTabbedPaneUI.setRolloverTab(SynthTabbedPaneUI.java:498)
at javax.swing.plaf.basic.BasicTabbedPaneUI.setRolloverTab(BasicTabbedPaneUI.java:558)
at javax.swing.plaf.basic.BasicTabbedPaneUI.access$2000(BasicTabbedPaneUI.java:37)
at javax.swing.plaf.basic.BasicTabbedPaneUI$Handler.mouseMoved(BasicTabbedPaneUI.java:3645)
at java.awt.Component.processMouseMotionEvent(Component.java:6333)
at javax.swing.JComponent.processMouseMotionEvent(JComponent.java:3285)
at java.awt.Component.processEvent(Component.java:6057)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4651)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4251)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:643)
at java.awt.EventQueue.access$000(EventQueue.java:84)
at java.awt.EventQueue$1.run(EventQueue.java:602)
at java.awt.EventQueue$1.run(EventQueue.java:600)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:616)
at java.awt.EventQueue$2.run(EventQueue.java:614)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:613)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
在BoxLayout (size = ...行)中从该方法抛出
public Dimension preferredLayoutSize(Container target) {
Dimension size;
synchronized(this) {
checkContainer(target);
checkRequests();
size = new Dimension(xTotal.preferred, yTotal.preferred);
}
扩展布局管理器来提供同步是不太可能有效的。验证所有 GUI组件都是在事件分派线程上构造的。同样，使用invokeLater()或SwingWorker，验证所有数据模型是否在事件调度线程上更新。由于失败可能是模糊的，@mKorbel提出的这个问题探讨了以编程方式发现EDT违规的方法。
如果您能到达那一行，那么很可能xTotal。preferred为null或yTotal。
从我看到的代码量来看，我猜您正在尝试使用swing组件而不使用事件调度线程。
这会导致像上面那样难看的异常。我在一个项目中遇到了这个问题，我意识到已经太晚了，无法修复它，所以我只是把所有东西都放在try cat中，没有打印整个堆栈跟踪…
如果这确实是问题，你可以捕获并忽略空指针异常。
最好的方法是使用事件分派线程
因为错误发生在Swing"内部"(堆栈跟踪中只有java*类)，所以我将非常仔细地检查我的代码，以确保所有Swing调用都发生在EDT上。