How To Create Coordinates In Two-dimensional Grid

how to create coordinates in a two-dimensional grid, in the end it shall look like A5, F6 and so on. The aim is to place 3 DotComs in this grid by coincidence. To do this one uses two arrays. One array represents one DotCom, the other represents the grid's size, in this case 49 (7x7).The code ends like this:

ArrayList<String> alphaCells = new ArrayList<String>();
...
int x = 0;
int row = 0;
int column = 0;
while (x<comSize) {
grid[coords[x]] = 1; // mark master grid points as used
row = (int)(coords[x] / gridLength);
column = coords[x] % gridLength;
temp = String.valueOf(alphabet.charAt(column));
alphaCells.add(temp.concat(Integer.toString(row));
x++;
}
return alphaCells;
}

why row and column are calculated like this. Furthermore I don't understand why the column is used to generate a character, because columns are marked with numbers and rows are marked with characters.