public void setKey(ByteBuffer key, int offset, int length, short rowLen) {
    this.buf = key;
    this.offset = offset;
    this.length = length;
    this.rowLen = rowLen;
  }
A setter that helps to avoid object creation every time and whenever there is a need to create
new OffheapKeyOnlyKeyValue.
@param key    - the key part of the cell
@param offset - offset of the cell
@param length - length of the cell
@param rowLen - the rowlen part of the cell
hbase-common/src/main/java/org/apache/hadoop/hbase/ByteBufferKeyOnlyKeyValue.java