8263481: Specification of JComponent::setDefaultLocale doesn't mention that passing 'null' restores VM's default locale

Reviewed-by: aivanov

Author: prsadhuk

src/java.desktop/share/classes/javax/swing/JComponent.java

@@ -2851,6 +2851,8 @@ public static Locale getDefaultLocale() {
      * potentially multiple lightweight applications running in a single VM)
      * can have their own setting. An applet can safely alter its default
      * locale because it will have no affect on other applets (or the browser).
+     * Passing {@code null} will reset the current locale back
+     * to VM's default locale.
      *
      * @param l the desired default <code>Locale</code> for new components.
      * @see #getDefaultLocale

test/jdk/javax/swing/JComponent/TestNullLocale.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2021, 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 8263481
+   @summary Verifies calling setDefaultLocale(null) will reset
+            to VM's default locale
+   @run main TestNullLocale
+ */
+
+import javax.swing.JComponent;
+import java.util.Locale;
+
+public class TestNullLocale {
+    public static void main(String[] args) {
+        Locale defaultLocale = JComponent.getDefaultLocale();
+        JComponent.setDefaultLocale(Locale.GERMAN);
+        JComponent.setDefaultLocale(null);
+        Locale currentLocale = JComponent.getDefaultLocale();
+        if (defaultLocale != currentLocale) {
+            System.out.println("currentLocale " + currentLocale);
+            System.out.println("defaultLocale " + defaultLocale);
+            throw new RuntimeException("locale not reset to default locale");
+        }
+    }
+}
+
+