7123229: (coll) EnumMap.containsValue(null) returns true

Summary: java.util.EnumMap.NULL equals() must only be true for itself
Reviewed-by: alanb, mduigou
Contributed-by: NNeil Richards <neil.richards@ngmr.net>

src/share/classes/java/util/EnumMap.java

@@ -106,7 +106,15 @@ public class EnumMap<K extends Enum<K>, V> extends AbstractMap<K, V>
     /**
      * Distinguished non-null value for representing null values.
      */
-    private static final Object NULL = new Integer(0);
+    private static final Object NULL = new Object() {
+        public int hashCode() {
+            return 0;
+        }
+
+        public String toString() {
+            return "java.util.EnumMap.NULL";
+        }
+    };
 
     private Object maskNull(Object value) {
         return (value == null ? NULL : value);

test/java/util/EnumMap/UniqueNullValue.java

+/*
+ * Copyright (c) 2012, 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.
+ */
+
+/*
+ * Portions Copyright (c) 2012, IBM Corporation
+ */
+
+/*
+ * @test
+ * @bug 7123229
+ * @summary (coll) EnumMap.containsValue(null) returns true
+ * @author ngmr
+ */
+
+import java.util.EnumMap;
+import java.util.Map;
+
+public class UniqueNullValue {
+    static enum TestEnum { e00, e01 }
+
+    public static void main(String[] args) {
+        Map<TestEnum, Integer> map = new EnumMap<>(TestEnum.class);
+
+        map.put(TestEnum.e00, 0);
+        if (false == map.containsValue(0)) {
+            throw new RuntimeException("EnumMap unexpectedly missing 0 value");
+        }
+        if (map.containsValue(null)) {
+            throw new RuntimeException("EnumMap unexpectedly holds null value");
+        }
+
+        map.put(TestEnum.e00, null);
+        if (map.containsValue(0)) {
+            throw new RuntimeException("EnumMap unexpectedly holds 0 value");
+        }
+        if (false == map.containsValue(null)) {
+            throw new RuntimeException("EnumMap unexpectedly missing null value");
+        }
+    }
+}