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

*** 138,147 ****
--- 138,148 ----
       */
      public static final Duration ZERO = new Duration(0, 0);
      /**
       * Serialization version.
       */
+     @java.io.Serial
      private static final long serialVersionUID = 3078945930695997490L;
      /**
       * Constant for nanos per second.
       */
      private static final BigInteger BI_NANOS_PER_SECOND = BigInteger.valueOf(NANOS_PER_SECOND);
*** 1527,1546 ****
--- 1528,1549 ----
       *  out.writeInt(nanos);
       * </pre>
       *
       * @return the instance of {@code Ser}, not null
       */
+     @java.io.Serial
      private Object writeReplace() {
          return new Ser(Ser.DURATION_TYPE, this);
      }
  
      /**
       * 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");
      }
  
      void writeExternal(DataOutput out) throws IOException {