设计模式(3)-策略模式(Strategy) (六)

Rental::Rental(Movie movie, int daysRented)
{
qDebug()<<"construct Rental";
_movie = movie;
_daysRented = daysRented;
}

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

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

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

main.cpp

[html]
#include
#include "movie.h"
#include "rental.h"
#include "regularprice.h"
#include "newreleaseprice.h"
#include "discountprice.h"

int main()
{
int daysRented = 30;
Movie movie("Book1",NEW_RELEASE);
Rental rental(movie,daysRented);
movie.setPriceCode(NEW_RELEASE, new NewReleasePrice);
rental.getCharge(daysRented);
return 0;
}
#include
#include "movie.h"
#include "rental.h"
#include "regularprice.h"
#include "newreleaseprice.h"
#include "discountprice.h"

int main()
{
int daysRented = 30;
Movie movie("Book1",NEW_RELEASE);
Rental rental(movie,daysRented);
movie.setPriceCode(NEW_RELEASE, new NewReleasePrice);
rental.getCharge(daysRented);
return 0;
}

【运行结果】

[html]
"construct Movie::Movie(Book1,1)"
construct Price
construct Movie::Movie()
construct Rental
construct Price
construct NewReleasePrice
NewReleasePrice::getCharge
"construct Movie::Movie(Book1,1)"
construct Price
construct Movie::Movie()
construct Rental
construct Price
construct NewReleasePrice
NewReleasePrice::getCharge

【结果分析】

[html]
movie.setPriceCode(NEW_RELEASE, new NewReleasePrice);
movie.setPriceCode(NEW_RELEASE, new NewReleasePrice);
传入priceCode和Price子对象作为参数，从运行结果可以看出，调用了NewReleasePrice的getCharge方法。

应用策略模式后，Rental::getCharge中仅有一行代码。

[html] view plaincopyprint double Rental::getCharge(int daysRented)
{
return _movie.getCharge(daysRented);
}
double Rental::getCharge(int daysRented)
{
return _movie.getCharge(daysRented);
}
将原来的getCharge做了搬移处理，而Movie::getCharge也很简短：

[html] view plaincopyprint double Movie::getCharge(int daysRented)
{
return _price->getCharge(daysRented);
}
double Movie::getCharge(int daysRented)
{
return _price->getCharge(daysRented);
}

*应用策略模式后，消除了switch-case语句，函数更为简洁。将Price单独抽出，成为一个类组，提高了代码的可重用性。

作者：tandesir