code: public static Writable newInstance(Class<? extends Writable> c,
        Configuration conf, boolean supportJobConf) {
      WritableFactory factory = WritableFactories.getFactory(c);
      if (factory != null) {
        Writable result = factory.newInstance();
        if (result instanceof Configurable) {
          ((Configurable) result).setConf(conf);
        }
        return result;
      } else {
        return ReflectionUtils.newInstance(c, conf, supportJobConf);
      }
    }
docs: Create a new instance of a class with a defined factory.