java - Applet : visually bugs out only in browser, 并从 Swing 抛出异常

Question

我们一直在办公室里苦苦挣扎，因为我们的一个(大型)小程序中存在一个看似无法解决的错误，这个小程序是 MS Word 的 Java 模拟，用于考试。这个异常似乎源于 Swing 本身，我不确定如何解决它。发生的情况如下:

小程序加载时会显示加载屏幕，直至 100%。此后，组件全部以损坏的方式显示，就好像它们的某些绘制方法没有被正确调用一样，将光标悬停在某些按钮等上确实会使它们闪烁/显示一段时间。大约每隔一秒就会有一个异常打印到控制台。 (见下文)此错误不会出现在 Eclipse 中，只会出现在浏览器中。

摘要:Applet 组件都是毫无异常(exception)地构建的，但是在某个组件的每次“绘制”调用中(我假设)，它会在视觉上出现错误，并且每秒都会打印以下内容:

Exception in thread "AWT-EventQueue-11" java.lang.ClassCastException: javax.swing.JLabel cannot be cast to javax.swing.text.JTextComponent
 at javax.swing.text.html.EditableView.paint(Unknown Source)
 at javax.swing.text.BoxView.paintChild(Unknown Source)
 at javax.swing.text.BoxView.paint(Unknown Source)
 at javax.swing.text.BoxView.paintChild(Unknown Source)
 at javax.swing.text.BoxView.paint(Unknown Source)
 at javax.swing.text.ParagraphView.paint(Unknown Source)
 at javax.swing.text.html.ParagraphView.paint(Unknown Source)
 at javax.swing.text.BoxView.paintChild(Unknown Source)
 at javax.swing.text.BoxView.paint(Unknown Source)
 at javax.swing.text.html.BlockView.paint(Unknown Source)
 at javax.swing.text.BoxView.paintChild(Unknown Source)
 at javax.swing.text.BoxView.paint(Unknown Source)
 at javax.swing.text.html.BlockView.paint(Unknown Source)
 at javax.swing.plaf.basic.BasicHTML$Renderer.paint(Unknown Source)
 at javax.swing.plaf.basic.BasicLabelUI.paint(Unknown Source)
 at javax.swing.plaf.ComponentUI.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.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.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$3.run(Unknown Source)
 at javax.swing.RepaintManager$3.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.access$1000(Unknown Source)
 at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
 at java.awt.event.InvocationEvent.dispatch(Unknown Source)
 at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
 at java.awt.EventQueue.access$200(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(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)

非常感谢您的帮助，因为这让我发疯，我似乎找不到触发此问题的原因，因为代码来自以前的开发人员，而且一团糟。我尝试过不同的JDK版本。

谢谢。

Answer 1

java.lang.ClassCastException: javax.swing.JLabel cannot be cast to javax.swing.text.JTextComponent

• 查看 JTextComponents 的组件树，没有 JLabel，JLabel 不是 JTextComponents 的成员

• 最安全的可能是在任何转换之前测试 if (Xxx instanceof JTextComponent)