code: private MRCompactorJobRunner getMRCompactorJobRunner(Dataset dataset) {
      try {
        @SuppressWarnings("unchecked")
        Class<? extends MRCompactorJobRunner> cls = (Class<? extends MRCompactorJobRunner>) Class
            .forName(this.state.getProp(COMPACTION_JOB_RUNNER_CLASS, DEFAULT_COMPACTION_JOB_RUNNER_CLASS));
        return cls.getDeclaredConstructor(Dataset.class, FileSystem.class).newInstance(dataset, this.fs);
      } catch (Exception e) {
        throw new RuntimeException("Cannot instantiate MRCompactorJobRunner", e);
      }
    }
docs: Get an instance of {@link MRCompactorJobRunner}.