src/java.base/share/classes/java/util/Hashtable.java

*** 169,178 ****
--- 169,179 ----
       * the Hashtable fail-fast.  (See ConcurrentModificationException).
       */
      private transient int modCount = 0;
  
      /** use serialVersionUID from JDK 1.0.2 for interoperability */
+     @java.io.Serial
      private static final long serialVersionUID = 1421746759512286392L;
  
      /**
       * Constructs a new, empty hashtable with the specified initial
       * capacity and the specified load factor.
*** 1199,1208 ****
--- 1200,1210 ----
       *             <i>size</i> of the Hashtable (the number of key-value
       *             mappings), followed by the key (Object) and value (Object)
       *             for each key-value mapping represented by the Hashtable
       *             The key-value mappings are emitted in no particular order.
       */
+     @java.io.Serial
      private void writeObject(java.io.ObjectOutputStream s)
              throws IOException {
          writeHashtable(s);
      }
  
*** 1252,1261 ****
--- 1254,1264 ----
      }
  
      /**
       * Reconstitute the Hashtable from a stream (i.e., deserialize it).
       */
+     @java.io.Serial
      private void readObject(java.io.ObjectInputStream s)
              throws IOException, ClassNotFoundException {
          readHashtable(s);
      }