6672644: JComboBox still scrolling if switch to another window and return back

src/java.desktop/share/classes/javax/swing/plaf/basic/BasicScrollBarUI.java

@@ -31,6 +31,7 @@
 import java.awt.Dimension;
 import java.awt.Graphics;
 import java.awt.Insets;
+import java.awt.KeyboardFocusManager;
 import java.awt.LayoutManager;
 import java.awt.Point;
 import java.awt.Rectangle;
@@ -122,6 +123,8 @@ public class BasicScrollBarUI
     protected ArrowButtonListener buttonListener;
     /** Model listener */
     protected ModelListener modelListener;
+    /** KeyboardFocusListener */
+    protected KeyboardFocusListener keyboardFocusListener;
 
     /** Thumb rectangle */
     protected Rectangle thumbRect;
@@ -356,12 +359,15 @@ protected void installListeners(){
         buttonListener = createArrowButtonListener();
         modelListener = createModelListener();
         propertyChangeListener = createPropertyChangeListener();
+        keyboardFocusListener = createKeyboardFocusListener();
 
         scrollbar.addMouseListener(trackListener);
         scrollbar.addMouseMotionListener(trackListener);
         scrollbar.getModel().addChangeListener(modelListener);
         scrollbar.addPropertyChangeListener(propertyChangeListener);
         scrollbar.addFocusListener(getHandler());
+        KeyboardFocusManager.getCurrentKeyboardFocusManager()
+                .addPropertyChangeListener(keyboardFocusListener);
 
         if (incrButton != null) {
             incrButton.addMouseListener(buttonListener);
@@ -443,6 +449,8 @@ protected void uninstallListeners() {
             incrButton.removeMouseListener(buttonListener);
         }
 
+        KeyboardFocusManager.getCurrentKeyboardFocusManager()
+                .removePropertyChangeListener(keyboardFocusListener);
         scrollbar.getModel().removeChangeListener(modelListener);
         scrollbar.removeMouseListener(trackListener);
         scrollbar.removeMouseMotionListener(trackListener);
@@ -509,6 +517,14 @@ protected PropertyChangeListener createPropertyChangeListener() {
         return getHandler();
     }
 
+    /**
+     * Creates a keyboard focus listener.
+     * @return a keyboard focus listener
+     */
+    protected KeyboardFocusListener createKeyboardFocusListener() {
+        return new KeyboardFocusListener();
+    }
+
     private void updateThumbState(int x, int y) {
         Rectangle rect = getThumbBounds();
 
@@ -1202,6 +1218,35 @@ public boolean getSupportsAbsolutePositioning() {
         return supportsAbsolutePositioning;
     }
 
+    /**
+     * A listener to listen for keyboard focus changes.
+     */
+    protected class KeyboardFocusListener implements PropertyChangeListener {
+        /**
+         * Constructs a {@code KeyboardFocusListener}.
+         */
+        protected KeyboardFocusListener() {}
+
+        @Override
+        public void propertyChange(PropertyChangeEvent e) {
+            String propertyName = e.getPropertyName();
+
+            if ("focusOwner" == propertyName) {
+                // Stop scrolling if no longer focus owner
+                if (e.getNewValue() == null && scrollTimer.isRunning()) {
+                    scrollTimer.stop();
+                    buttonListener.handledEvent = false;
+                    scrollbar.setValueIsAdjusting(false);
+                    if (incrButton.getModel().isPressed()) {
+                        incrButton.getModel().setPressed(false);
+                    } else if (decrButton.getModel().isPressed()) {
+                        decrButton.getModel().setPressed(false);
+                    }
+                }
+            }
+        }
+    }
+
     /**
      * A listener to listen for model changes.
      */

test/jdk/javax/swing/JComboBox/JComboBoxScrollFocusTest.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2024, 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.
+ */
+
+import javax.swing.JComboBox;
+import javax.swing.JFrame;
+
+/*
+ * @test
+ * @bug 6672644
+ * @library /java/awt/regtesthelpers
+ * @build PassFailJFrame
+ * @summary Tests JComboBox scrollbar behavior when alt-tabbing
+ * @requires os.family != "mac"
+ * @run main/manual JComboBoxScrollFocusTest
+ */
+
+public class JComboBoxScrollFocusTest {
+    private static final String INSTRUCTIONS =
+            """
+             Click on the dropdown button for the JComboBox in the test frame.
+             Then, press and hold the left click button on the down arrow button
+             in the popup list. While holding the left click button, the list
+             should be scrolling down. Press ALT + TAB while holding down the
+             left click to switch focus to a different window. Then release the
+             left click button. Focus the test frame again and click the
+             dropdown button for the JComboBox again. The list should be
+             stationary and not be automatically scrolling.
+
+             If you are able to execute all steps successfully then the test
+             passes, otherwise it fails.
+            """;
+
+    public static void main(String[] args) throws Exception {
+        PassFailJFrame
+                .builder()
+                .title("JComboBoxScrollFocusTest Test Instructions")
+                .instructions(INSTRUCTIONS)
+                .columns(40)
+                .testUI(JComboBoxScrollFocusTest::createAndShowGUI)
+                .build()
+                .awaitAndCheck();
+    }
+
+    private static JFrame createAndShowGUI() {
+        JFrame frame = new JFrame("JComboBoxScrollFocusTest Test Frame");
+        JComboBox<String> combobox = new JComboBox<>();
+        for (int i = 0; i < 100; i++) {
+            combobox.addItem(String.valueOf(i));
+        }
+        frame.add(combobox);
+        frame.setSize(400, 200);
+        frame.setLocationRelativeTo(null);
+        return frame;
+    }
+}