@Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("source columns: " + Arrays.toString(sourceColumns));
    sb.append(", ");
    sb.append("output columns: " + Arrays.toString(outputColumns));
    sb.append(", ");
    sb.append("type infos: " + Arrays.toString(typeInfos));
    return sb.toString();
  }
This class collects column information for copying a row from one VectorizedRowBatch to
same/another batch.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorColumnMapping.java