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

*** 89,98 ****
--- 89,99 ----
  
  public class HashSet<E>
      extends AbstractSet<E>
      implements Set<E>, Cloneable, java.io.Serializable
  {
+     @java.io.Serial
      static final long serialVersionUID = -5024744406713321676L;
  
      private transient HashMap<E,Object> map;
  
      // Dummy value to associate with an Object in the backing Map
*** 269,278 ****
--- 270,280 ----
       *             (int), and its load factor (float) are emitted, followed by
       *             the size of the set (the number of elements it contains)
       *             (int), followed by all of its elements (each an Object) in
       *             no particular order.
       */
+     @java.io.Serial
      private void writeObject(java.io.ObjectOutputStream s)
          throws java.io.IOException {
          // Write out any hidden serialization magic
          s.defaultWriteObject();
  
*** 290,299 ****
--- 292,302 ----
  
      /**
       * Reconstitute the {@code HashSet} instance from a stream (that is,
       * deserialize it).
       */
+     @java.io.Serial
      private void readObject(java.io.ObjectInputStream s)
          throws java.io.IOException, ClassNotFoundException {
          // Read in any hidden serialization magic
          s.defaultReadObject();