1、享元模式提出

面向对象很好地解决了抽象问题，但是创建对象会带来一定的内存开销。绝大部分情况下，创建对象带来的内存开销是可以忽略不计的；在有些情况下是需要谨慎处理的，如类A的sizeof是50个字节，则创建50*1024*100个A对象，则对象的内存大小约为5MB，这个是很占用内存的。享元模式就是使用运用共享技术支持创建大量的对象情况，并同时减少内存开销。

2、需求描述

有3种类型产品，这几种类型产品的形状和大小各不相同；现有1000个产品（3种类型），分别输出这些产品的类型和大小。

3、享元模式的代码实现

#include <iostream>
#include <string>
#include <map>
#include <vector>
namespace FlyWeight {
const std::string strG1="G1";
const std::string strG2="G2";
const std::string strG3="G3";class AbsProduct
{
public:virtual void Shape()=0;virtual void Size()=0;std::string m_strType;virtual ~AbsProduct(){};
};class ProductA:public AbsProduct
{
public:virtual void Shape(){std::cout << "rectangle" << std::endl;};virtual void Size(){std::cout << "60*60" << std::endl;};
};class ProductB:public AbsProduct
{
public:virtual void Shape(){std::cout << "triangle" << std::endl;};virtual void Size(){std::cout << "30*40*50" << std::endl;};
};class ProductC:public AbsProduct
{
public:virtual void Shape(){std::cout << "polygon" << std::endl;};virtual void Size(){std::cout << "30*40*50*60*60" << std::endl;};
};class ProductFact
{private:std::map<std::string,AbsProduct*>mapProduts;
public:AbsProduct* GetProduct(std::string strType){auto it = mapProduts.find(strType);if(it != mapProduts.end()){return it->second;}else{AbsProduct* newProduct = nullptr;if(strG1 == strType){newProduct = new ProductA();}else if(strG2 == strType){newProduct = new ProductB();}else{newProduct = new ProductC();}mapProduts[strType] = newProduct;return newProduct;}};void clear()
{for(auto it = mapProduts.begin(); it != mapProduts.end(); it++){delete (it->second);it->second = nullptr;}
}
};
}std::vector<std::string>vecProducts;
int main()
{for(int i = 0; i < 1000* 1; i++){if(i % 3 == 0){vecProducts.emplace_back(FlyWeight::strG1);}else if(i % 3 == 1){vecProducts.emplace_back(FlyWeight::strG2);}else{vecProducts.emplace_back(FlyWeight::strG3);}}FlyWeight::ProductFact obj;for(auto it = vecProducts.begin(); it != vecProducts.end();it++){std::cout << "\n";FlyWeight::AbsProduct *objIter= obj.GetProduct(*it);std::cout << objIter << std::endl;objIter->Size();objIter->Shape();}obj.clear();vecProducts.clear();return 0;
}

运行结果如下：