@Override
    public TsFileResource next() {
      if (!hasNext()) {
        throw new NoSuchElementException();
      }
      return this.tsFileResourceList.get(currentIndex++);
    }
insert tsFileResource to a target pos(targetPos = index) e.g. if index = 0, then to the first,
if index = 1, then to the second.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/tsfile/TsFileResourceList.java