Validate () tree throws NullPointerException when changing L & F?

Question

public class TabbedArea extends JTabbedPane { public void addArea(){ add(component); final JPanel panel = new JPanel(new BorderLayout()); panel.add(new JLabel(title), BorderLayout.LINE_START); JButton closeButton = new JButton(new CloseIcon()); closeButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { removeArea(subAreas.get(indexOfTabComponent(panel))); } }); panel.add(closeButton, BorderLayout.LINE_END); setTabComponentAt(getTabCount() - 1, panel); } } public class LnFManager { public void setTheme(PlasticTheme theme){ for (Window window : Window.getWindows()) { if (window.isDisplayable()) SwingUtilities.updateComponentTreeUI(window); } } } 

When setTheme () is called, it triggers a repeat of this event (presumably for each component):

 Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at javax.swing.plaf.basic.BasicTabbedPaneUI.scrollableTabLayoutEnabled(BasicTabbedPaneUI.java:263) at javax.swing.plaf.basic.BasicTabbedPaneUI.access$400(BasicTabbedPaneUI.java:54) at javax.swing.plaf.basic.BasicTabbedPaneUI$TabContainer.doLayout(BasicTabbedPaneUI.java:3850) at java.awt.Container.validateTree(Container.java:1568) at java.awt.Container.validateTree(Container.java:1575) at java.awt.Container.validateTree(Container.java:1575) at java.awt.Container.validateTree(Container.java:1575) at java.awt.Container.validateTree(Container.java:1575) at java.awt.Container.validate(Container.java:1540) at javax.swing.SwingUtilities.updateComponentTreeUI(SwingUtilities.java:1227) at flextrade.tca.ui.LnFManager.setTheme(LnFManager.java:113) at flextrade.tca.ui.ToolBar$15.actionPerformed(ToolBar.java:803) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2012) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2335) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:404) at javax.swing.JToggleButton$ToggleButtonModel.setPressed(JToggleButton.java:308) at javax.swing.AbstractButton.doClick(AbstractButton.java:374) at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:829) at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:873) at java.awt.Component.processMouseEvent(Component.java:6108) at javax.swing.JComponent.processMouseEvent(JComponent.java:3267) at java.awt.Component.processEvent(Component.java:5873) at java.awt.Container.processEvent(Container.java:2105) at java.awt.Component.dispatchEventImpl(Component.java:4469) at java.awt.Container.dispatchEventImpl(Container.java:2163) at java.awt.Component.dispatchEvent(Component.java:4295) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4461) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4125) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4055) at java.awt.Container.dispatchEventImpl(Container.java:2149) at java.awt.Window.dispatchEventImpl(Window.java:2478) at java.awt.Component.dispatchEvent(Component.java:4295) at java.awt.EventQueue.dispatchEvent(EventQueue.java:604) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177) at java.awt.EventDispatchThread.run(EventDispatchThread.java:138) 

Commenting out the string 'setTabComponentAt (getTabCount () - 1, panel); throws the exception from the exception (but this, of course, violates the user interface), and also overrides updateUI () in the TabbedArea class and exits super.updateUI () in SwingUtilities.invokeLater (..).

This is similar to the error that the jEdit team had with one of its plugins when updating L & F. However, their solution was simply not to update the appearance of the application at runtime and rely on a restart to do this.

Does anyone have any ideas how this can be solved without having to reboot to change the look?

Answer 1

Looking at the source for Java 6, I found that line 263 of BasicTabbedPaneUI is a return statement:

  /* In an attempt to preserve backward compatibility for programs * which have extended BasicTabbedPaneUI to do their own layout, the * UI uses the installed layoutManager (and not tabLayoutPolicy) to * determine if scrollTabLayout is enabled. */ private boolean scrollableTabLayoutEnabled() { return (tabPane.getLayout() instanceof TabbedPaneScrollLayout); } 

The only thing that your NPE can trigger is that the tabPane link is NULL. Without additional information, all I can guess is that you removed the tab component without deleting the corresponding tab.