src/java.base/share/classes/java/lang/Integer.java

@@ -24,12 +24,14 @@
   */
  
  package java.lang;
  
  import jdk.internal.misc.CDS;
+ import jdk.internal.misc.PreviewFeatures;
  import jdk.internal.misc.VM;
  import jdk.internal.util.DecimalDigits;
+ import jdk.internal.value.DeserializeConstructor;
  import jdk.internal.vm.annotation.ForceInline;
  import jdk.internal.vm.annotation.IntrinsicCandidate;
  import jdk.internal.vm.annotation.Stable;
  
  import java.lang.annotation.Native;

@@ -54,14 +56,22 @@
   * an {@code int} to a {@code String} and a {@code String} to an
   * {@code int}, as well as other constants and methods useful when
   * dealing with an {@code int}.
   *
   * <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 Integer} 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>
   *
   * <p>Implementation note: The implementations of the "bit twiddling"
   * methods (such as {@link #highestOneBit(int) highestOneBit} and
   * {@link #numberOfTrailingZeros(int) numberOfTrailingZeros}) are
   * based on material from Henry S. Warren, Jr.'s <cite>Hacker's

@@ -72,10 +82,11 @@
   * @author  Arthur van Hoff
   * @author  Josh Bloch
   * @author  Joseph D. Darcy
   * @since 1.0
   */
+ @jdk.internal.MigratedValueClass
  @jdk.internal.ValueBased
  public final class Integer extends Number
          implements Comparable<Integer>, Constable, ConstantDesc {
      /**
       * A constant holding the minimum value an {@code int} can

@@ -984,27 +995,42 @@
          private IntegerCache() {}
      }
  
      /**
       * Returns an {@code Integer} instance representing the specified
-      * {@code int} value.  If a new {@code Integer} instance is not
-      * required, this method should generally be used in preference to
-      * the constructor {@link #Integer(int)}, as this method is likely
-      * to yield significantly better space and time performance by
-      * caching frequently requested values.
-      *
-      * This method will always cache values in the range -128 to 127,
-      * inclusive, and may cache other values outside of this range.
+      * {@code int} value.
+      * <div class="preview-block">
+      *      <div class="preview-comment">
+      *          <p>
+      *              - When preview features are NOT enabled, {@code Integer} is an identity class.
+      *              If a new {@code Integer} instance is not
+      *              required, this method should generally be used in preference to
+      *              the constructor {@link #Integer(int)}, as this method is likely
+      *              to yield significantly better space and time performance by
+      *              caching frequently requested values.
+      *              This method will always cache values in the range -128 to 127,
+      *              inclusive, and may cache other values outside of this range.
+      *          </p>
+      *          <p>
+      *              - When preview features are enabled, {@code Integer} is a {@linkplain Class#isValue value class}.
+      *              The {@code valueOf} behavior is the same as invoking the constructor,
+      *              whether cached or not.
+      *          </p>
+      *      </div>
+      * </div>
       *
       * @param  i an {@code int} value.
       * @return an {@code Integer} instance representing {@code i}.
       * @since  1.5
       */
      @IntrinsicCandidate
+     @DeserializeConstructor
      public static Integer valueOf(int i) {
-         if (i >= IntegerCache.low && i <= IntegerCache.high)
-             return IntegerCache.cache[i + (-IntegerCache.low)];
+         if (!PreviewFeatures.isEnabled()) {
+             if (i >= IntegerCache.low && i <= IntegerCache.high)
+                 return IntegerCache.cache[i + (-IntegerCache.low)];
+         }
          return new Integer(i);
      }
  
      /**
       * The value of the {@code Integer}.