8369184: SimpleTimeZone equals() Returns True for Unequal Instances with Different hashCode Values

Backport-of: 37b725d9c12834358a562e6c03fb7f566d639ca5

Author: Kieran Farrell

src/java.base/share/classes/java/util/SimpleTimeZone.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1996, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2025, 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
@@ -112,15 +112,15 @@
  * <pre><code>
  *      // Base GMT offset: -8:00
  *      // DST starts:      at 2:00am in standard time
- *      //                  on the first Sunday in April
+ *      //                  on the second Sunday in March
  *      // DST ends:        at 2:00am in daylight time
- *      //                  on the last Sunday in October
+ *      //                  on the first Sunday in November
  *      // Save:            1 hour
  *      SimpleTimeZone(-28800000,
  *                     "America/Los_Angeles",
- *                     Calendar.APRIL, 1, -Calendar.SUNDAY,
+ *                     Calendar.MARCH, 8, -Calendar.SUNDAY,
  *                     7200000,
- *                     Calendar.OCTOBER, -1, Calendar.SUNDAY,
+ *                     Calendar.NOVEMBER, 1, -Calendar.SUNDAY,
  *                     7200000,
  *                     3600000)
  *
@@ -863,13 +863,24 @@ public Object clone()
     }
 
     /**
-     * Generates the hash code for the SimpleDateFormat object.
+     * Generates the hash code for the SimpleTimeZone object.
      * @return the hash code for this object
      */
     public int hashCode()
     {
-        return startMonth ^ startDay ^ startDayOfWeek ^ startTime ^
-            endMonth ^ endDay ^ endDayOfWeek ^ endTime ^ rawOffset;
+        int hash = 31 * getID().hashCode() + rawOffset;
+        hash = 31 * hash + Boolean.hashCode(useDaylight);
+        if (useDaylight) {
+            hash = 31 * hash + startMonth;
+            hash = 31 * hash + startDay;
+            hash = 31 * hash + startDayOfWeek;
+            hash = 31 * hash + startTime;
+            hash = 31 * hash + endMonth;
+            hash = 31 * hash + endDay;
+            hash = 31 * hash + endDayOfWeek;
+            hash = 31 * hash + endTime;
+        }
+        return hash;
     }
 
     /**

test/jdk/java/util/TimeZone/SimpleTimeZoneEqualsHashCodeTest.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2025, 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 8369184
+ * @summary Checks if equals()/hashCode() of SimpleTimeZone works correctly
+ * @run junit SimpleTimeZoneEqualsHashCodeTest
+ */
+
+import java.util.SimpleTimeZone;
+import static java.util.Calendar.MARCH;
+import static java.util.Calendar.NOVEMBER;
+import static java.util.Calendar.SUNDAY;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class SimpleTimeZoneEqualsHashCodeTest {
+    private static final SimpleTimeZone STZ_WITH_DST =
+        new SimpleTimeZone(-288_000_000, "America/Los_Angeles",
+            MARCH, 8, -SUNDAY, 7_200_000,
+            NOVEMBER, 1, -SUNDAY, 7_200_000);
+    private static final SimpleTimeZone STZ_WITHOUT_DST =
+        new SimpleTimeZone(0, "foo");
+
+    @Test
+    void withDSTTest() {
+        var stz = (SimpleTimeZone)STZ_WITH_DST.clone();
+        assertEquals(STZ_WITH_DST, stz);
+        assertEquals(STZ_WITH_DST.hashCode(), stz.hashCode());
+
+        stz.setEndRule(NOVEMBER, 8, -SUNDAY, 7_200_000);
+        assertNotEquals(STZ_WITH_DST, stz);
+        // From the contract point, hash codes may be the same.
+        // This tests the implementation which considers DST
+        // related fields for calculating the hash code.
+        assertNotEquals(STZ_WITH_DST.hashCode(), stz.hashCode());
+    }
+
+    @Test
+    void withoutDSTTest() {
+        var stz = (SimpleTimeZone)STZ_WITHOUT_DST.clone();
+
+        // Only setting start rule. Still considered non-DST zone
+        stz.setStartRule(MARCH, 8, -SUNDAY, 7_200_000);
+        assertTrue(!stz.useDaylightTime());
+        assertEquals(STZ_WITHOUT_DST, stz);
+        assertEquals(STZ_WITHOUT_DST.hashCode(), stz.hashCode());
+
+        // Setting end rule as well. Now it is considered DST zone
+        stz.setEndRule(NOVEMBER, 8, -SUNDAY, 7_200_000);
+        assertTrue(stz.useDaylightTime());
+        assertNotEquals(STZ_WITHOUT_DST, stz);
+        // From the contract point, hash codes may be the same.
+        // This tests the implementation which considers DST
+        // related fields for calculating the hash code.
+        assertNotEquals(STZ_WITHOUT_DST.hashCode(), stz.hashCode());
+    }
+}