《重构--改善既有代码的设计》读书笔记之四：将条件分支语句放入合适类中

要点：最好不要在另一个对象的属性基础上运用条件分支语句，如果不得不使用，也应该在对象自己的数据上使用。

方法：getCharge() 和 getFrequentRenterPoints()移动到Movie类中去。

在运用继承重构代码之前 rental & movie 代码如下：

rental.h:

#ifndef RENTAL_H
#define RENTAL_H

#include "movie.h"

class Rental
{
public:
Rental(Movie movie, int daysRented);
double getCharge();
int getDaysRented();
Movie getMovie();
int getFrequentRenterPoints();

private:
Movie _movie;
int _daysRented;
};

#endif //RENTAL_H

rental.cpp:

#include "rental.h"

Rental::Rental(Movie movie, int daysRented)
{
_movie = movie;
_daysRented = daysRented;
}

double Rental::getCharge()
{
return _movie.getCharge(_daysRented);
}

int Rental::getDaysRented()
{
return _daysRented;
}

Movie Rental::getMovie()
{
return _movie;
}

int Rental::getFrequentRenterPoints()
{
return _movie.getFrequentRenterPoints(_daysRented);
}

movie.h:

#ifndef MOVIE_H
#define MOVIE_H

#include <string>

using std::string;

class Movie
{
public:
Movie(string title = "empty", int priceCode = 0);
double getCharge(int daysRented);
int getFrequentRenterPoints(int daysRented);
int getPriceCode();
void setPriceCode(int arg);
string getTitle();

public:
static const int REGULAR;
static const int NEW_RELEASE;
static const int CHILDRENS;

private:
string _title;
int _priceCode;
};

#endif //MOVIE_H

movie.cpp:

#include "movie.h"

const int Movie::REGULAR = 0;
const int Movie::NEW_RELEASE = 1;
const int Movie::CHILDRENS = 2;

Movie::Movie(string title , int priceCode)
{
_title = title;
_priceCode = priceCode;
}

double Movie::getCharge(int daysRented)
{
double result = 0;

// determine amounts for each line
switch(getPriceCode())
{
case REGULAR:
result += 2;
if (daysRented > 2)
{
result += (daysRented - 2) * 1.5;
}
break;
case NEW_RELEASE:
result += daysRented * 3;
break;
case CHILDRENS:
result += 1.5;
if (daysRented > 3)
{
result += (daysRented - 3) * 1.5;
}
break;
}

return result;
}

int Movie::getFrequentRenterPoints(int daysRented)
{

// add bonus for a two day new release rental
if ((getPriceCode() == NEW_RELEASE) && daysRented > 1)
return 2;
else
return 1;
}

int Movie::getPriceCode()
{
return _priceCode;
}

void Movie::setPriceCode(int arg)
{
_priceCode = arg;
}

string Movie::getTitle()
{
return _title;
}