public Coordinate addDirection(DIRECTION d) {
        int newX = 0, newY = 0;
        if (d == DIRECTION.NORTH) {
            newY--;
        } else if (d == DIRECTION.EAST) {
            newX++;
        } else if (d == DIRECTION.SOUTH) {
            newY++;
        } else if (d == DIRECTION.WEST) {
            newX--;
        }

        newX = newX + x;
        newY = newY + y;

        if (newX < 0 || newX >= 20 || newY < 0 || newY >= 20) {
            return null;
        }

        return new Coordinate(newX, newY);
    }