目录

C++设计模式-享元（Flyweight）

一、意图

二、适用性

三、结构

四、参与者

五、代码

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C++设计模式-享元（Flyweight）

一、意图

运用共享技术有效地支持大量细粒度的对象。

二、适用性

• 一个应用程序使用了大量的对象。
• 完全由于使用大量的对象，造成很大的存储开销。
• 对象的大多数状态都可变为外部状态。
• 如果删除对象的外部状态，那么可以用相对较少的共享对象取代很多组对象。
• 应用程序不依赖于对象标识。由于Flyweight对象可以被共享，对于概念上明显有别的对象，标识测试将返回真值。

三、结构

 

四、参与者

• Flyweight

       描述一个接口，通过这个接口flyweight可以接受并作用于外部状态。

• ConcreteFlyweight

        实现Flyweight接口，并为内部状态（如果有的话）增加存储空间。ConcreteFlyweight对象必须是可共享的。它所存储的状态必须是内部的；即，它必须独立于ConcreteFlyweight对象的场景。

• UnsharedConcreteFlyweight

        并非所有的Flyweight子类都需要被共享。Flyweight接口使共享成为可能，但它并不强制共享。在Flyweight对象结构的某些层次，UnsharedConcreteFlyweight对象通常将ConcreteFlyweight对象作为子节点。

• FlyweightFactory

        创建并管理flyweight对象。

        确保合理地共享flyweight。当用户请求一个flyweight时，FlyweightFactory对象提供一个已创建的实例或者创建一个（如果不存在的话）。

• Client

        维持一个对flyweight的引用。

        计算或存储一个（多个）flyweight的外部状态。

五、代码

#include<iostream>
#include<vector>
using namespace std;class Flyweight {
public:Flyweight(string tempIntrinsicState) {this->intrinsicState = tempIntrinsicState;}string GetIntrinsicState() {return intrinsicState;}virtual void Operation(const string& tempExtrinsicState) = 0;
private:string intrinsicState;
};class ConcreteFlyweight :public Flyweight {
public:ConcreteFlyweight(string tempIntrinsicState) :Flyweight(tempIntrinsicState) {}void Operation(const string& tempExtrinsicState) {cout << this->GetIntrinsicState() << endl;cout << tempExtrinsicState << endl;}
};class UnsharedConcreteFlyweight : public Flyweight {
public:UnsharedConcreteFlyweight(string tempIntrinsicState) :Flyweight(tempIntrinsicState) {}void UnsharedConcreteOperation(const string& tempExtrinsicState) {cout << tempExtrinsicState << endl;}
};class FlyweightFactory {
public:Flyweight* GetFlyweight(string state) {vector<Flyweight*>::iterator it = this->flyweightVector.begin();for (; it != this->flyweightVector.end(); it++) {if ((*it)->GetIntrinsicState() == state) {return *it;}}Flyweight* flyweight = new ConcreteFlyweight(state);this->flyweightVector.push_back(flyweight);return flyweight;}int GetFlyweightCount() {return this->flyweightVector.size();}
private:vector<Flyweight*> flyweightVector;
};int main() {string extrinsicState = "ExtrinsicState";FlyweightFactory* flyweightFactory = new FlyweightFactory();Flyweight* flyweight1 = flyweightFactory->GetFlyweight("AAA");Flyweight* flyweight2 = flyweightFactory->GetFlyweight("AAA");Flyweight* flyweight3 = flyweightFactory->GetFlyweight("BBB");flyweight1->Operation(extrinsicState);cout << flyweightFactory->GetFlyweightCount() << endl;cout << (flyweight1 == flyweight2) << endl;return 0;
}