@Override
  protected T getCell(int i) {
    if ((i < minCellIdx) || (i >= maxCellIdx)) return null;
    return block[i];
  }
CellArrayMap is a simple array of Cells and cannot be allocated off-heap. As all java arrays
CellArrayMap's array of references pointing to Cell objects.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/CellArrayMap.java