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

*** 252,261 ****
--- 252,262 ----
          entry("HST", "-10:00")
      );
      /**
       * Serialization version.
       */
+     @java.io.Serial
      private static final long serialVersionUID = 8352817235686L;
  
      //-----------------------------------------------------------------------
      /**
       * Gets the system default time-zone.
*** 622,631 ****
--- 623,633 ----
       * Defend against malicious streams.
       *
       * @param s the stream to read
       * @throws InvalidObjectException always
       */
+     @java.io.Serial
      private void readObject(ObjectInputStream s) throws InvalidObjectException {
          throw new InvalidObjectException("Deserialization via serialization delegate");
      }
  
      /**
*** 653,662 ****
--- 655,665 ----
       * ID has a valid format, but is not in the known set of region-based IDs.
       *
       * @return the instance of {@code Ser}, not null
       */
      // this is here for serialization Javadoc
+     @java.io.Serial
      private Object writeReplace() {
          return new Ser(Ser.ZONE_REGION_TYPE, this);
      }
  
      abstract void write(DataOutput out) throws IOException;