src/java.base/share/classes/sun/net/www/http/KeepAliveCache.java

*** 47,56 ****
--- 47,57 ----
   * @author Dave Brown
   */
  public class KeepAliveCache
      extends HashMap<KeepAliveKey, ClientVector>
      implements Runnable {
+     @java.io.Serial
      private static final long serialVersionUID = -2937172892064557949L;
  
      /* maximum # keep-alive connections to maintain at once
       * This should be 2 by the HTTP spec, but because we don't support pipe-lining
       * a larger value is more appropriate. So we now set a default of 5, and the value
*** 201,214 ****
--- 202,217 ----
      }
  
      /*
       * Do not serialize this class!
       */
+     @java.io.Serial
      private void writeObject(ObjectOutputStream stream) throws IOException {
          throw new NotSerializableException();
      }
  
+     @java.io.Serial
      private void readObject(ObjectInputStream stream)
          throws IOException, ClassNotFoundException
      {
          throw new NotSerializableException();
      }
*** 216,225 ****
--- 219,229 ----
  
  /* FILO order for recycling HttpClients, should run in a thread
   * to time them out.  If > maxConns are in use, block.
   */
  class ClientVector extends ArrayDeque<KeepAliveEntry> {
+     @java.io.Serial
      private static final long serialVersionUID = -8680532108106489459L;
  
      // sleep time in milliseconds, before cache clear
      int nap;
  
*** 266,279 ****
--- 270,285 ----
      }
  
      /*
       * Do not serialize this class!
       */
+     @java.io.Serial
      private void writeObject(ObjectOutputStream stream) throws IOException {
          throw new NotSerializableException();
      }
  
+     @java.io.Serial
      private void readObject(ObjectInputStream stream)
          throws IOException, ClassNotFoundException
      {
          throw new NotSerializableException();
      }