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