public Object[] randomRow(boolean allowNull) {

    final Object row[] = new Object[columnCount];
    for (int c = 0; c < columnCount; c++) {
      row[c] = randomWritable(typeInfos[c], objectInspectorList.get(c), allowNull);
    }
    return row;
  }
Generate object inspector and random row object[].
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/VectorRandomRowSource.java