public Object getValue() {
    switch (type) {
    case LONG:
      return getLongValue();
    case DOUBLE:
      return getDoubleValue();
    case BYTES:
      return getBytesValue();
    case DECIMAL:
      return getDecimalValue();
    case TIMESTAMP:
      return getTimestampValue();
    case INTERVAL_DAY_TIME:
      return getIntervalDayTimeValue();
    default:
      throw new RuntimeException("Unexpected column vector type " + type);
    }
  }
Constant is represented as a vector with repeating values.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/ConstantVectorExpression.java