public void setStructValue(Object structValue) throws HiveException {
    StructTypeInfo structTypeInfo = (StructTypeInfo) outputTypeInfo;
    List<TypeInfo> fieldTypeInfoList = structTypeInfo.getAllStructFieldTypeInfos();
    final int size = fieldTypeInfoList.size();
    this.structValue = new ConstantVectorExpression[size];
    List<Object> fieldValueList = (List<Object>) structValue;
    for (int i = 0; i < size; i++) {
      this.structValue[i] = create(i, fieldValueList.get(i), fieldTypeInfoList.get(i));
    }
  }
Constant is represented as a vector with repeating values.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/ConstantVectorExpression.java