code: public void noteClassMappingsReceived (Collection<Class<?>> sclasses)
      {
          // sanity check
          if (_classmap == null) {
              throw new RuntimeException("Missing class map");
          }
  
          // make each class's code positive to signify that we no longer need to send metadata
          for (Class<?> sclass : sclasses) {
              ClassMapping cmap = _classmap.get(sclass);
              if (cmap == null) {
                  throw new RuntimeException("No class mapping for " + sclass.getName());
              }
              cmap.code = (short)Math.abs(cmap.code);
          }
      }
docs: Notes that the receiver has received the mappings for a group of classes and thus that from
  now on, only the codes need be sent.