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

@@ -252,10 +252,11 @@
         entry("HST", "-10:00")
     );
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = 8352817235686L;
 
     //-----------------------------------------------------------------------
     /**
      * Gets the system default time-zone.

@@ -622,10 +623,11 @@
      * 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");
     }
 
     /**

@@ -653,10 +655,11 @@
      * 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;