src/java.base/share/classes/java/time/Instant.java

*** 193,22 ***
   * The Java time-scale is used for all date-time classes.
   * This includes {@code Instant}, {@code LocalDate}, {@code LocalTime}, {@code OffsetDateTime},
   * {@code ZonedDateTime} and {@code Duration}.
   * <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.
!  * The {@code equals} method should be used for comparisons.
   *
   * @implSpec
   * This class is immutable and thread-safe.
   *
   * @since 1.8
   */
  @jdk.internal.ValueBased
  public final class Instant
          implements Temporal, TemporalAdjuster, Comparable<Instant>, Serializable {
  
      /**
       * Constant for the 1970-01-01T00:00:00Z epoch instant.
--- 193,30 ---
   * The Java time-scale is used for all date-time classes.
   * This includes {@code Instant}, {@code LocalDate}, {@code LocalTime}, {@code OffsetDateTime},
   * {@code ZonedDateTime} and {@code Duration}.
   * <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, mutexes, or
!  * with {@linkplain java.lang.ref.Reference object references}.
!  *
!  * <div class="preview-block">
+  *      <div class="preview-comment">
+  *          When preview features are enabled, {@code Instant} 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>
   *
   * @implSpec
   * This class is immutable and thread-safe.
   *
   * @since 1.8
   */
  @jdk.internal.ValueBased
+ @jdk.internal.MigratedValueClass
  public final class Instant
          implements Temporal, TemporalAdjuster, Comparable<Instant>, Serializable {
  
      /**
       * Constant for the 1970-01-01T00:00:00Z epoch instant.