code: public void swap(int i, int j) {
      checkBounds(i);
      checkBounds(j);
  
      if (i == j)
        return;
  
      copier.copy(tmp, offset(i));
      unsafe.copyMemory(null, offset(j), null, offset(i), elementSpacing);
      unsafe.copyMemory(tmp, firstFieldOffset, null, offset(j), elementSize);
    }
docs: Swaps two elements
  
  @param i Index of first element
  @param j Index of second element