Name: rmT116609 Date: 04/23/2003


FULL PRODUCT VERSION :
java version "1.4.2-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2-beta-b19)
Java HotSpot(TM) Client VM (build 1.4.2-beta-b19, mixed mode)

FULL OS VERSION :
Microsoft Windows 2000 [Version 5.00.2195]

A DESCRIPTION OF THE PROBLEM :
When in JFrame resides JComboBox somewhere, if leave corresponding popup menu opened and click on close button ("[x]"), then NullPointerException is rised in event dispatch thread. This bug is also exist in JDK 1.4.1_x.

After some digging in src.zip I have found source of this problem:

The code in the method java.awt.Container.removeNotify() makes local copy of object field ncomponents, but during invoking removeNotify() of nested components there is fired unexpected call of Container.remove() which is cause to modify fields "ncomponents" & "component". You can see stack trace for this call in example below.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run example from test case below: java FrameDemo. Then open popup window from JComboBox, and without closing it click on frame close button [X]. NPE is rised.

  To see source of the problem I have do following modifications in standart java.awt.Container:


    /**
     * Makes this Container undisplayable by removing its connection
     * to its native screen resource. Making a container undisplayable
     * will cause all of its children to be made undisplayable.
     * This method is called by the toolkit internally and should
     * not be called directly by programs.
     * @see Component#isDisplayable
     * @see #addNotify
     */
private boolean removeNotifyActive;

    public void removeNotify() {
        synchronized (getTreeLock()) {
int ncomponents = this.ncomponents;
            Component component[] = this.component;
removeNotifyActive=true;
for (int i = 0 ; i < ncomponents ; i++) {

if( ncomponents != this.ncomponents )
   System.out.println("Container.removeNotify(): ncomponents != this.ncomponents");

component[i].removeNotify();
}
removeNotifyActive=false;
if ( dispatcher != null ) {
dispatcher.dispose();
        dispatcher = null;
}
super.removeNotify();
        }
    }


    /**
     * Removes the component, specified by <code>index</code>,
     * from this container.
     * @param index the index of the component to be removed.
     * @see #add
     * @since JDK1.1
     */
    public void remove(int index) {

if( removeNotifyActive )
  {
   System.out.println("Container.remove("+index+") during removeNotify()!");
   new Exception("Container.remove("+index+") during removeNotify()!").printStackTrace();
  }

synchronized (getTreeLock()) {
            if (index < 0 || index >= ncomponents) {
                throw new ArrayIndexOutOfBoundsException(index);
            }
...

When running following example with this modifications you can see stack trace that produced the bug (java -Xbootclasspath/p:jvmdebug FrameDemo).


Output from java -Xbootclasspath/p:jvmdebug FrameDemo:

Container.remove(0) during removeNotify()!
Container.removeNotify(): ncomponents != this.ncomponents
java.lang.Exception: Container.remove(0) during removeNotify()!
at java.awt.Container.remove(Container.java:714)
at javax.swing.JLayeredPane.remove(JLayeredPane.java:219)
...[Skipped, full dump below]...
java.lang.NullPointerException
at java.awt.Container.removeNotify(Container.java:2082)
at javax.swing.JComponent.removeNotify(JComponent.java:4307)
...[Skipped, full dump below]...


ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.lang.Exception: Container.remove(0) during removeNotify()!
at java.awt.Container.remove(Container.java:714)
at javax.swing.JLayeredPane.remove(JLayeredPane.java:219)
at java.awt.Container.remove(Container.java:776)
at javax.swing.PopupFactory$ContainerPopup.hide(PopupFactory.java:461)
at javax.swing.PopupFactory$LightWeightPopup.hide(PopupFactory.java:654)
at javax.swing.JPopupMenu.setVisible(JPopupMenu.java:762)
at javax.swing.JPopupMenu.menuSelectionChanged(JPopupMenu.java:1270)
at javax.swing.MenuSelectionManager.setSelectedPath(MenuSelectionManager.java:77)
at javax.swing.MenuSelectionManager.clearSelectedPath(MenuSelectionManager.java:109)
at javax.swing.plaf.basic.BasicComboPopup.hide(BasicComboPopup.java:189)
at javax.swing.plaf.basic.BasicComboBoxUI.setPopupVisible(BasicComboBoxUI.java:929)
at javax.swing.JComboBox.setPopupVisible(JComboBox.java:790)
at javax.swing.JComboBox.hidePopup(JComboBox.java:783)
at javax.swing.JComboBox$1.ancestorRemoved(JComboBox.java:218)
at javax.swing.AncestorNotifier.fireAncestorRemoved(AncestorNotifier.java:90)
at javax.swing.AncestorNotifier.propertyChange(AncestorNotifier.java:213)
at javax.swing.event.SwingPropertyChangeSupport.firePropertyChange(SwingPropertyChangeSupport.java:264)
at javax.swing.event.SwingPropertyChangeSupport.firePropertyChange(SwingPropertyChangeSupport.java:232)
at javax.swing.JComponent.firePropertyChange(JComponent.java:3822)
at javax.swing.JComponent.removeNotify(JComponent.java:4311)
at java.awt.Container.removeNotify(Container.java:2082)
at javax.swing.JComponent.removeNotify(JComponent.java:4307)
at java.awt.Container.removeNotify(Container.java:2082)
at javax.swing.JComponent.removeNotify(JComponent.java:4307)
at java.awt.Container.removeNotify(Container.java:2082)
at javax.swing.JComponent.removeNotify(JComponent.java:4307)
at java.awt.Container.removeNotify(Container.java:2082)
at javax.swing.JComponent.removeNotify(JComponent.java:4307)
at javax.swing.JRootPane.removeNotify(JRootPane.java:691)
at java.awt.Container.removeNotify(Container.java:2082)
at java.awt.Frame.removeNotify(Frame.java:866)
at java.awt.Window$1DisposeAction.run(Window.java:557)
at java.awt.Window.dispose(Window.java:570)
at FrameDemo$1.windowClosing(FrameDemo.java:18)
at java.awt.AWTEventMulticaster.windowClosing(AWTEventMulticaster.java:291)
at java.awt.Window.processWindowEvent(Window.java:1121)
at javax.swing.JFrame.processWindowEvent(JFrame.java:266)
at java.awt.Window.processEvent(Window.java:1079)
at java.awt.Component.dispatchEventImpl(Component.java:3614)
at java.awt.Container.dispatchEventImpl(Container.java:1634)
at java.awt.Window.dispatchEventImpl(Window.java:1606)
at java.awt.Component.dispatchEvent(Component.java:3476)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:456)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)
java.lang.NullPointerException
at java.awt.Container.removeNotify(Container.java:2082)
at javax.swing.JComponent.removeNotify(JComponent.java:4307)
at java.awt.Container.removeNotify(Container.java:2082)
at javax.swing.JComponent.removeNotify(JComponent.java:4307)
at javax.swing.JRootPane.removeNotify(JRootPane.java:691)
at java.awt.Container.removeNotify(Container.java:2082)
at java.awt.Frame.removeNotify(Frame.java:866)
at java.awt.Window$1DisposeAction.run(Window.java:557)
at java.awt.Window.dispose(Window.java:570)
at FrameDemo$1.windowClosing(FrameDemo.java:18)
at java.awt.AWTEventMulticaster.windowClosing(AWTEventMulticaster.java:291)
at java.awt.Window.processWindowEvent(Window.java:1121)
at javax.swing.JFrame.processWindowEvent(JFrame.java:266)
at java.awt.Window.processEvent(Window.java:1079)
at java.awt.Component.dispatchEventImpl(Component.java:3614)
at java.awt.Container.dispatchEventImpl(Container.java:1634)
at java.awt.Window.dispatchEventImpl(Window.java:1606)
at java.awt.Component.dispatchEvent(Component.java:3476)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:456)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class FrameDemo
{
 public static void main(String s[])
 {
  final JFrame frame = new JFrame("JComboBox Bug");

  frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);

  frame.addWindowListener(new WindowAdapter()
  {
   public void windowClosing(WindowEvent evt)
   {
    frame.setVisible(false);
    frame.dispose();
   }
  });

  frame.setJMenuBar(new JMenuBar());

  JPanel panel = new JPanel(new FlowLayout());

  JComboBox combo = new JComboBox();
  combo.addItem("one");
  combo.addItem("two");
  combo.addItem("Three");

  panel.add(combo);

  frame.getContentPane().add(panel,BorderLayout.CENTER);

  frame.pack();
  frame.setSize(new Dimension(200,300));

  frame.setVisible(true);
 }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Before invoking dispose() you must somehow close the opened popup window. This can be done, for example, by tracing full tree of frame components and invoking hidePopup() in case of JComboBox component
(Review ID: 184677)
======================================================================