Review

class SegmentMerger {
      public void work(double units) throws MergeAbortedException {
        // do nothing
      }
}

class SegmentMerger {
        public void work(double units) throws MergeAbortedException {
          // do nothing
        }
}

class SegmentMerger.CheckAbort {
    /**
     * Records the fact that roughly units amount of work
     * have been done since this method was last called.
     * When adding time-consuming code into SegmentMerger,
     * you should test different values for units to ensure
     * that the time in between calls to merge.checkAborted
     * is up to ~ 1 second.
     */
    public void work(double units) throws MergePolicy.MergeAbortedException {
      workCount += units;
      if (workCount >= 10000.0) {
        merge.checkAborted(dir);
        workCount = 0;
      }
    }

}