private void setBorder() {

        for (int i=TOP_AND_LEFT_BORDER_SIZE-1; i< SIZE_OF_MATRIX; i+=2) {

            for (int k=TOP_AND_LEFT_BORDER_SIZE-1; k< SIZE_OF_MATRIX; k++) {

                matrix[i][k] = BORDER_MATERIAL;

            }

            for (int k=TOP_AND_LEFT_BORDER_SIZE; k< SIZE_OF_MATRIX; k++) {

                matrix[k][i] = BORDER_MATERIAL;

            }

        }

        char topCoord = FIRST_TOP_COORD;

        for (int i=TOP_AND_LEFT_BORDER_SIZE; i< SIZE_OF_MATRIX; i+=2) {

            matrix[0][i] = topCoord;
            topCoord++;

        }

        char leftCoord = FIRST_LEFT_COORD;

        for (int i=TOP_AND_LEFT_BORDER_SIZE; i< SIZE_OF_MATRIX; i+=2) {

            matrix[i][0] = leftCoord;
            leftCoord++;

        }

    }