public void init(TypeInfo typeInfo, int outputColumnNum) throws HiveException {

    allocateArrays(1);
    initTargetEntry(0, outputColumnNum, typeInfo);
  }
This class assigns specified columns of a row from a Writable row objects.

The caller provides the data types and projection column numbers of a subset of the columns
to assign.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorAssignRow.java