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

*** 477,486 ****
--- 477,487 ----
      /**
       * Implementation of a clock that always returns the latest time from
       * {@link System#currentTimeMillis()}.
       */
      static final class SystemClock extends Clock implements Serializable {
+         @java.io.Serial
          private static final long serialVersionUID = 6740630888130243051L;
          private static final long OFFSET_SEED =
                  System.currentTimeMillis()/1000 - 1024; // initial offest
          static final SystemClock UTC = new SystemClock(ZoneOffset.UTC);
  
*** 570,579 ****
--- 571,581 ----
          }
          @Override
          public String toString() {
              return "SystemClock[" + zone + "]";
          }
+         @java.io.Serial
          private void readObject(ObjectInputStream is)
                  throws IOException, ClassNotFoundException {
              // ensure that offset is initialized
              is.defaultReadObject();
              offset = OFFSET_SEED;
*** 584,593 ****
--- 586,596 ----
      /**
       * Implementation of a clock that always returns the same instant.
       * This is typically used for testing.
       */
      static final class FixedClock extends Clock implements Serializable {
+         @java.io.Serial
          private static final long serialVersionUID = 7430389292664866958L;
          private final Instant instant;
          private final ZoneId zone;
  
          FixedClock(Instant fixedInstant, ZoneId zone) {
*** 634,643 ****
--- 637,647 ----
      //-----------------------------------------------------------------------
      /**
       * Implementation of a clock that adds an offset to an underlying clock.
       */
      static final class OffsetClock extends Clock implements Serializable {
+         @java.io.Serial
          private static final long serialVersionUID = 2007484719125426256L;
          private final Clock baseClock;
          private final Duration offset;
  
          OffsetClock(Clock baseClock, Duration offset) {
*** 684,693 ****
--- 688,698 ----
      //-----------------------------------------------------------------------
      /**
       * Implementation of a clock that adds an offset to an underlying clock.
       */
      static final class TickClock extends Clock implements Serializable {
+         @java.io.Serial
          private static final long serialVersionUID = 6504659149906368850L;
          private final Clock baseClock;
          private final long tickNanos;
  
          TickClock(Clock baseClock, long tickNanos) {