Flyweight模式

最新推荐文章于 2021-02-16 20:02:20 发布

转载最新推荐文章于 2021-02-16 20:02:20 发布 · 509 阅读

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http://blog.youkuaiyun.com/phoebin/article/details/3866404

Flyweight享元设计模式是一种结构型设计模式，它主要解决的问题是：由于（同类）对象的数量太大，采用面向对象时给系统带来了难以承受的内存开销。比如有这样一个场景：一个停车场中有1000辆汽车，我们所定义的汽车对象占用内存0.3M，那么要实例化1000辆就是300M。由此可见，在这种情况下采用一般的面向对象方式出现了大量细粒度的对象会很快充斥在系统中，从而带来很高的运行是代价（这里指的代价是内存开销的代价）。

GoF《设计模式》中说道：运用共享技术有效的支持大量细粒度的对象。

案例分析

定义一个场景：有一个汽车类型，客户程序要实例化20000个，实例化后查看一下内存分配情况。

#include "stdafx.h"
#include "windows.h"
#include "iostream.h"
#include <string>
#include <list>
#include <map>
#pragma warning (disable: 4786)

/*
class Car
{
    private:
    std::string Body;
    std::string Wheel;
    std::string Engine;
    std::string Brand;
   std::string Color;

    public:
    Car(std::string body,std::string wheel,std::string engine,std::string brand,std::string color)
    {
        Body = body;
       Wheel = wheel;
       Engine = engine;
       Brand = brand;
       Color = color;
    }

};

int main(int argc, char* argv[])
{
    unsigned long MemCount = 0;
    MEMORYSTATUS MemInfo;
    MemInfo.dwLength = sizeof(MEMORYSTATUS);
    GlobalMemoryStatus(&MemInfo);

    cout << "内存分配情况如下：" << endl;
    MemCount = MemInfo.dwAvailVirtual;
    cout << "实例化前：" << MemInfo.dwAvailVirtual << endl;

std::list<Car> m_list;

    for(int i = 0;i < 20000;i++)
    {
        Car * car = new Car("4.2M","Wheel","NeedForSpeed","BMW","Black");
       //m_list.push_back(*car);
    }

    GlobalMemoryStatus(&MemInfo);
   cout << "实例化后：" << MemInfo.dwAvailVirtual << endl;
    cout << "实例化后：" << MemCount - MemInfo.dwAvailVirtual << endl;

return 0;
}
*/

/*
内存分配情况如下：
实例化前：2140868608
实例化后：2125139968
实例化后：15728640
*/

class CarBody
{
     private:
     std::string Body;
     std::string Wheel;
     std::string Engine;
     std::string Color;

     public:
     CarBody(){};
     CarBody(std::string body,std::string wheel,std::string engine,std::string color)
   {
         Body = body;
         Wheel = wheel;
         Engine = engine;
         Color = color;
    }
};

class FlyWeightCar
{
     public:
     std::string Brand;
     CarBody * carbody;

public:
FlyWeightCar(){};
};

class FlyWeightFactory
{

private:
static FlyWeightCar * Car;
static std::map<std::string,FlyWeightCar> table;

public:
      static FlyWeightCar * CreateInit(std::string body,std::string wheel,std::string engine,std::string brand,std::string color)
     {
         FlyWeightCar * car = Car;
         if(brand.compare("BMW") == 0)
         {
             //car = &(FlyWeightCar)table[brand];
             car = Car;
        }
         else
        {
             car->Brand = brand;
             car->carbody = new CarBody(body,wheel,engine,color);
             std::pair<std::string,FlyWeightCar> item (brand, *car);
             table.insert(item);
          }
        return car;
    }
};

FlyWeightCar * FlyWeightFactory::Car = new FlyWeightCar();

std::map<std::string,FlyWeightCar> FlyWeightFactory::table;

int main(int argc, char* argv[])
{
     unsigned long MemCount = 0;
     MEMORYSTATUS MemInfo;
     MemInfo.dwLength = sizeof(MEMORYSTATUS);
     GlobalMemoryStatus(&MemInfo);

    cout << "内存分配情况如下：" << endl;
     MemCount = MemInfo.dwAvailVirtual;
     cout << "实例化前：" << MemInfo.dwAvailPhys << endl;

std::list<FlyWeightCar> m_list;

     for(int i = 0;i < 10000;i++)
     {
         FlyWeightCar * car = FlyWeightFactory::CreateInit("4.2M","Wheel","NeedForSpeed","Benz","Black");
         //m_list.push_back(*car);
     }

    for(i = 0;i < 10000;i++)
    {
         FlyWeightCar * car = FlyWeightFactory::CreateInit("4.2M","Wheel","NeedForSpeed","BMW","Black");
        //m_list.push_back(*car);
    }

    GlobalMemoryStatus(&MemInfo);
   cout << "实例化后：" << MemInfo.dwAvailPhys << endl;