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

*** 78,87 ****
--- 78,88 ----
   */
  public abstract class EnumSet<E extends Enum<E>> extends AbstractSet<E>
      implements Cloneable, java.io.Serializable
  {
      // declare EnumSet.class serialization compatibility with JDK 8
+     @java.io.Serial
      private static final long serialVersionUID = 1009687484059888093L;
  
      /**
       * The class of all the elements of this set.
       */
*** 447,466 ****
--- 448,469 ----
           *
           * @return a {@code EnumSet} object with initial state
           * held by this proxy
           */
          @SuppressWarnings("unchecked")
+         @java.io.Serial
          private Object readResolve() {
              // instead of cast to E, we should perhaps use elementType.cast()
              // to avoid injection of forged stream, but it will slow the
              // implementation
              EnumSet<E> result = EnumSet.noneOf(elementType);
              for (Enum<?> e : elements)
                  result.add((E)e);
              return result;
          }
  
+         @java.io.Serial
          private static final long serialVersionUID = 362491234563181265L;
      }
  
      /**
       * Returns a
*** 469,486 ****
--- 472,491 ----
       * representing the state of this instance.
       *
       * @return a {@link SerializationProxy}
       * representing the state of this instance
       */
+     @java.io.Serial
      Object writeReplace() {
          return new SerializationProxy<>(this);
      }
  
      /**
       * @param s the stream
       * @throws java.io.InvalidObjectException always
       */
+     @java.io.Serial
      private void readObject(java.io.ObjectInputStream s)
          throws java.io.InvalidObjectException {
          throw new java.io.InvalidObjectException("Proxy required");
      }
  }