public void setConcat(int elementNum, byte[] leftSourceBuf, int leftStart, int leftLen,
      byte[] rightSourceBuf, int rightStart, int rightLen) {
    int newLen = leftLen + rightLen;
    ensureValPreallocated(newLen);
    setValPreallocated(elementNum, newLen);

    System.arraycopy(leftSourceBuf, leftStart, currentValue, currentOffset, leftLen);
    System.arraycopy(rightSourceBuf, rightStart, currentValue,
        currentOffset + leftLen, rightLen);
  }
Set a field to the concatenation of two string values. Result data is copied
into the internal buffer.

@param elementNum index within column vector to set
@param leftSourceBuf container of left argument
@param leftStart start of left argument
@param leftLen length of left argument
@param rightSourceBuf container of right argument
@param rightStart start of right argument
@param rightLen length of right argument
storage-api/src/java/org/apache/hadoop/hive/ql/exec/vector/BytesColumnVector.java