@Override
  public String vectorExpressionParameters() {
    if (fieldStart == -1) {
      return getColumnParamString(0, inputColumnNum[0]);
    } else {
      return getColumnParamString(0, inputColumnNum[0]) + ", fieldStart " + fieldStart + ", fieldLength " + fieldLength;
    }
  }
Abstract class to return various fields from a String.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/VectorUDFTimestampFieldString.java