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

@@ -24,10 +24,12 @@
   */
  
  package java.lang;
  
  import jdk.internal.misc.CDS;
+ import jdk.internal.misc.PreviewFeatures;
+ import jdk.internal.value.DeserializeConstructor;
  import jdk.internal.vm.annotation.IntrinsicCandidate;
  import jdk.internal.vm.annotation.Stable;
  
  import java.lang.constant.Constable;
  import java.lang.constant.DynamicConstantDesc;

@@ -164,26 +166,34 @@
   * {@code char} values that are code units of the <em>UTF-16</em>
   * encoding. For more information on Unicode terminology, refer to the
   * <a href="http://www.unicode.org/glossary/">Unicode Glossary</a>.
   *
   * <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 Character} 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>
   *
   * @spec https://www.unicode.org/reports/tr44 Unicode Character Database
   * @author  Lee Boynton
   * @author  Guy Steele
   * @author  Akira Tanaka
   * @author  Martin Buchholz
   * @author  Ulf Zibis
   * @since   1.0
   */
+ @jdk.internal.MigratedValueClass
  @jdk.internal.ValueBased
- public final
- class Character implements java.io.Serializable, Comparable<Character>, Constable {
+ public final class Character implements java.io.Serializable, Comparable<Character>, Constable {
      /**
       * The minimum radix available for conversion to and from strings.
       * The constant value of this field is the smallest value permitted
       * for the radix argument in radix-conversion methods such as the
       * {@code digit} method, the {@code forDigit} method, and the

@@ -9260,28 +9270,42 @@
      }
  
      /**
       * Returns a {@code Character} instance representing the specified
       * {@code char} value.
-      * If a new {@code Character} instance is not required, this method
-      * should generally be used in preference to the constructor
-      * {@link #Character(char)}, 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 {@code
-      * '\u005Cu0000'} to {@code '\u005Cu007F'}, inclusive, and may
-      * cache other values outside of this range.
+      * <div class="preview-block">
+      *      <div class="preview-comment">
+      *          <p>
+      *              - When preview features are NOT enabled, {@code Character} is an identity class.
+      *              If a new {@code Character} instance is not required, this method
+      *              should generally be used in preference to the constructor
+      *              {@link #Character(char)}, 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 {@code
+      *              '\u005Cu0000'} to {@code '\u005Cu007F'}, inclusive, and may
+      *              cache other values outside of this range.
+      *          </p>
+      *          <p>
+      *             - When preview features are enabled, {@code Character} 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  c a char value.
       * @return a {@code Character} instance representing {@code c}.
       * @since  1.5
       */
      @IntrinsicCandidate
+     @DeserializeConstructor
      public static Character valueOf(char c) {
-         if (c <= 127) { // must cache
-             return CharacterCache.cache[(int)c];
+         if (!PreviewFeatures.isEnabled()) {
+             if (c <= 127) { // must cache
+                 return CharacterCache.cache[(int) c];
+             }
          }
          return new Character(c);
      }
  
      /**