8269172: Add java.util.Objects.newIdentity method

Reviewed-by: mchung

Author: Roger Riggs

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

@@ -423,20 +423,6 @@ public static long getObjectSize(Object o) {
         return Unsafe.getUnsafe().getObjectSize(o);
     }
 
-    /**
-     * Returns a new Object implementing the {@code IdentityObject} interface.
-     * The object is a unique {@link IdentityObject} suitable for all purposes
-     * for which {@code new Object{}} was used including synchronization,
-     * mutexes and unique placeholders.
-     *
-     * @return a new Object implementing the IdentityObject interface
-     * @since Valhalla
-     */
-    public static IdentityObject newIdentity() {
-        // Return a new instance of an anonymous inner class.
-        return new IdentityObject() { };
-    }
-
     /**
      * Checks if the {@code index} is within the bounds of the range from
      * {@code 0} (inclusive) to {@code length} (exclusive).
@@ -512,4 +498,15 @@ long checkFromToIndex(long fromIndex, long toIndex, long length) {
     long checkFromIndexSize(long fromIndex, long size, long length) {
         return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
     }
+    /**
+     * {@return a new instance of an unspecified class}
+     * The object has a unique identity; no other references to it exist.
+     * It can be used for synchronization, or where a placeholder Object is needed.
+     * Use this method to avoid relying on the {@linkplain Object#Object() Object constructor}.
+     *
+     * @since 17
+     */
+    public static Object newIdentity() {
+        return new Object() {};
+    }
 }

test/jdk/java/util/Objects/BasicObjectsTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2009, 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
@@ -45,6 +45,7 @@ public static void main(String... args) {
         errors += testIsNull();
         errors += testNonNull();
         errors += testNonNullOf();
+        errors += testNewIdentity();
         if (errors > 0 )
             throw new RuntimeException();
     }
@@ -275,4 +276,19 @@ private static int testNonNullOf() {
         }
         return errors;
     }
+
+    private static int testNewIdentity() {
+        int errors = 0;
+
+        Object o1 = Objects.newIdentity();
+        Object o2 = Objects.newIdentity();
+
+        if (o1 == null || o2 == null)
+            errors += 1;
+
+        if (o1 == o2)
+            errors += 1;
+
+        return errors;
+    }
 }