code: public synchronized ByteBuffer getRecordBuffer(int x, int y) throws IOException {
      if(x >= matrixsize || y >= matrixsize) {
        throw new ArrayIndexOutOfBoundsException();
      }
      return array.getRecordBuffer(computeOffset(x, y));
    }
docs: Get a record buffer
  
  @param x First coordinate
  @param y Second coordinate
  @return Byte buffer for the record
  @throws IOException on IO errors