private void putMarkInTheRandomPlace (Square square, Mark mark) {

        Random rand = new Random(System.currentTimeMillis());

        do {

            switch (rand.nextInt(3)) {

                case 0:
                    mark.setLeftCoord('1');
                    break;
                case 1:
                    mark.setLeftCoord('2');
                    break;
                case 2:
                    mark.setLeftCoord('3');
                    break;
                default:
            }

            switch (rand.nextInt(3)) {

                case 0:
                    mark.setTopCoord('a');
                    break;
                case 1:
                    mark.setTopCoord('b');
                    break;
                case 2:
                    mark.setTopCoord('c');
                    break;
                default:
            }
        } while (!square.emptyCell(mark.getLeftCoord(),mark.getTopCoord()));

        square.putMark(mark);

    }