--- a/jdk/src/share/classes/javax/swing/plaf/basic/BasicComboPopup.java	Tue Jul 13 17:26:34 2010 +0400
+++ b/jdk/src/share/classes/javax/swing/plaf/basic/BasicComboPopup.java	Thu Jul 29 19:34:03 2010 +0400
@@ -202,8 +202,8 @@
      * Implementation of ComboPopup.show().
      */
     public void show() {
+        comboBox.firePopupMenuWillBecomeVisible();
         setListSelection(comboBox.getSelectedIndex());
-
         Point location = getPopupLocation();
         show( comboBox, location.x, location.y );
     }
@@ -344,7 +344,8 @@
 
     protected void firePopupMenuWillBecomeVisible() {
         super.firePopupMenuWillBecomeVisible();
-        comboBox.firePopupMenuWillBecomeVisible();
+        // comboBox.firePopupMenuWillBecomeVisible() is called from BasicComboPopup.show() method
+        // to let the user change the popup menu from the PopupMenuListener.popupMenuWillBecomeVisible()
     }
 
     protected void firePopupMenuWillBecomeInvisible() {

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/test/javax/swing/JComboBox/4743225/bug4743225.java	Thu Jul 29 19:34:03 2010 +0400
@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/* @test
+ * @bug 4743225
+ * @summary Size of JComboBox list is wrong when list is populated via PopupMenuListener
+ * @author Alexander Potochkin
+ */
+
+import sun.awt.SunToolkit;
+
+import javax.accessibility.AccessibleContext;
+import javax.swing.JComboBox;
+import javax.swing.JFrame;
+import javax.swing.SwingUtilities;
+import javax.swing.event.PopupMenuEvent;
+import javax.swing.event.PopupMenuListener;
+import javax.swing.plaf.basic.BasicComboPopup;
+import java.awt.FlowLayout;
+import java.awt.Point;
+import java.awt.Robot;
+import java.awt.Toolkit;
+import java.awt.event.InputEvent;
+
+public class bug4743225 extends JFrame {
+
+    private static JComboBox cb;
+    private static volatile boolean flag;
+
+    public bug4743225() {
+        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+        setLayout(new FlowLayout());
+        cb = new JComboBox(new Object[] {"one", "two", "three"});
+        cb.addPopupMenuListener(new PopupMenuListener() {
+            public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
+                cb.addItem("Test");
+            }
+
+            public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
+            }
+
+            public void popupMenuCanceled(PopupMenuEvent e) {
+            }
+        });
+        add(cb);
+        pack();
+    }
+
+    public static BasicComboPopup getPopup() {
+        AccessibleContext c = cb.getAccessibleContext();
+        for(int i = 0; i < c.getAccessibleChildrenCount(); i ++) {
+            if (c.getAccessibleChild(i) instanceof BasicComboPopup) {
+                return (BasicComboPopup) c.getAccessibleChild(i);
+            }
+        }
+        throw new AssertionError("No BasicComboPopup found");
+    }
+
+    public static void main(String... args) throws Exception {
+
+        Robot robot = new Robot();
+        robot.setAutoDelay(20);
+        SunToolkit toolkit = (SunToolkit) Toolkit.getDefaultToolkit();
+
+        SwingUtilities.invokeAndWait(new Runnable() {
+            public void run() {
+                new bug4743225().setVisible(true);
+            }
+        });
+        toolkit.realSync();
+
+        // calling this method from main thread is ok
+        Point point = cb.getLocationOnScreen();
+        robot.mouseMove(point.x + 10, point.y + 10);
+        robot.mousePress(InputEvent.BUTTON1_MASK);
+        robot.mouseRelease(InputEvent.BUTTON1_MASK);
+        toolkit.realSync();
+
+        SwingUtilities.invokeAndWait(new Runnable() {
+            public void run() {
+                if(getPopup().getList().getLastVisibleIndex() == 3) {
+                    flag = true;
+                }
+            }
+        });
+
+        if (!flag) {
+            throw new RuntimeException("The ComboBox popup wasn't correctly updated");
+        }
+    }
+}