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

@@ -40,24 +40,33 @@
   * (returns a default value if no value is present) and
   * {@link #ifPresent(LongConsumer) ifPresent()} (performs an
   * action if a value is present).
   *
   * <p>This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
-  * class; programmers should treat instances that are
-  * {@linkplain #equals(Object) equal} as interchangeable and should not
-  * use instances for synchronization, or unpredictable behavior may
-  * occur. For example, in a future release, synchronization may fail.
+  * class; programmers should treat instances that are {@linkplain #equals(Object) equal}
+  * as interchangeable and should not use instances for synchronization, mutexes, or
+  * with {@linkplain java.lang.ref.Reference object references}.
+  *
+  * <div class="preview-block">
+  *      <div class="preview-comment">
+  *          When preview features are enabled, {@code OptionalLong} is a {@linkplain Class#isValue value class}.
+  *          Use of value class instances for synchronization, mutexes, or with
+  *          {@linkplain java.lang.ref.Reference object references} result in
+  *          {@link IdentityException}.
+  *      </div>
+  * </div>
   *
   * @apiNote
   * {@code OptionalLong} is primarily intended for use as a method return type where
   * there is a clear need to represent "no result." A variable whose type is
   * {@code OptionalLong} should never itself be {@code null}; it should always point
   * to an {@code OptionalLong} instance.
   *
   * @since 1.8
   */
  @jdk.internal.ValueBased
+ @jdk.internal.MigratedValueClass
  public final class OptionalLong {
      /**
       * Common instance for {@code empty()}.
       */
      private static final OptionalLong EMPTY = new OptionalLong();