code: @SuppressWarnings("unchecked")
    public Class<? extends Reducer<?,?,?,?>> getReducerClass() 
       throws ClassNotFoundException {
      return (Class<? extends Reducer<?,?,?,?>>) 
        conf.getClass(REDUCE_CLASS_ATTR, Reducer.class);
    }
docs: Get the {@link Reducer} class for the job.
  
  @return the {@link Reducer} class for the job.