@Override
    protected String generateRandomNonNullValue(Random rand) {
      int length = rand.nextInt(20) + 5;
      char[] values = new char[length];
      for (int j = 0; j < length; j++) {
        switch (rand.nextInt(3)) {
        case 0:
          values[j] = (char) (rand.nextInt((int) 'z' - (int) 'a') + (int) 'a');
          break;
        case 1:
          values[j] = (char) (rand.nextInt((int) 'Z' - (int) 'A') + (int) 'A');
          break;
        case 2:
          values[j] = (char) (rand.nextInt((int) '9' - (int) '0') + (int) '0');
          break;
        default:
          throw new UnsupportedOperationException();
        }
      }
      return new String(values);
    }
Base class for type specific batch generators. Each type specific batch generator implements
generateRandomNonNullValue to generate random values, and initializeFixedPointValues to
specify a set of fixed values within the data (this is useful when defining query predicates)
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/util/OrcFileGenerator.java