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

@@ -90,10 +90,11 @@
 final class ZoneRegion extends ZoneId implements Serializable {
 
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = 8386373296231747096L;
     /**
      * The time-zone ID, not null.
      */
     private final String id;

@@ -187,20 +188,22 @@
      *  out.writeUTF(zoneId);
      * </pre>
      *
      * @return the instance of {@code Ser}, not null
      */
+    @java.io.Serial
     private Object writeReplace() {
         return new Ser(Ser.ZONE_REGION_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");
     }
 
     @Override