一、意图
定义一系列的算法，把它们一个个封装起来，并且使它们可相互替换，本模式使得算法可独立于使用它的客户而变化——四人团
二、基本思想
定义算法家族，分别封装起来，让它们之间可以互相替换，让算法的变化，不会影响到使用算法的用户。
三、优缺点分析
GOOD:
（1）策略模式是一种定义一系列算法的方法，从概念上看，所有这些算法完成的都是相同的工作，只是实现不同。
所以使用策略模式，就可以以相同的方式调用所有的算法，减少了各种算法类与使用算法类之间的耦合。
（2）策略模式的Strategy类层次为Context定义了一系列的可供重用的算法或行为。继承有助于析取出这些算法中的公共功能
（3）简化了单元测试（因为每个算法都有自己的类，可以通过自己的接口单独测试）
BUG:客户端要做出判断使用哪个具体算法（可通过在context中与工厂模式的结合来消除这个问题，虽然当新增加需求时，还是要改context中的代码，但是任何需求的变更本身就是需要成本的）
四、适用情况
策略模式和简单工厂基本相同，但简单工厂模式只能解决对象创建问题，对于类中的成员以方法为主，而且算法经常变动的类，应使用策略模式。
在实践中，策略模式实际上可以封装几乎任何类型的规则，只要在分析过程中听到需要不同时间应用不同的业务规则，就可以考虑使用策略模式处理这种变化的可能性。
五、标准UML图例及源码
（1）标准UML图列
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（2）标准源码
1: /************************************************************************
2: * FileName : Strategy.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 抽象算法类：定义所有支持的算法的公共接口
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef STRATEGY_H
8: #define STRATEGY_H
9:
10: class Strategy
11: {
12: public:
13: virtual ~Strategy(){}
14: // 算法方法
15: virtual void AlgorithmInterface() = 0;
16: };
17: #endif
1: /************************************************************************
2: * FileName : Context.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 上下文类，用一个ConcreateStrategy来配置，维护一个对Strategy对象的引用
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CONTEXT_H
8: #define CONTEXT_H
9:
10: #include "Strategy.h"
11: #include <iostream>
12:
13: class Context
14: {
15: public:
16: Context(Strategy *pStrategy);// 构造时，传入具体的策略对象
17: ~Context();
18:
19: void ContextInterface();// 根据具体的策略对象，调用其算法的方法
20: private:
21: Strategy* m_pStrategy;
22: };
23:
24: #endif // CONTEXT_H
1: /************************************************************************
2: * FileName : ConcreateStrategyA.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 具体算法类A：封装了具体的算法或行为，继承于Strategy
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CONCREATESTRATEGYA_H
8: #define CONCREATESTRATEGYA_H
9:
10: #include "Strategy.h"
11: #include <iostream>
12:
13: class ConcreateStrategyA
14: : public Strategy
15: {
16: public:
17: virtual ~ConcreateStrategyA(){}
18: // 算法A实现方法
19: virtual void AlgorithmInterface();
20: };
21:
22: #endif // CONCREATESTRATEGYA_H
1: /************************************************************************
2: * FileName : ConcreateStrategyB.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 具体算法类B：封装了具体的算法或行为，继承于Strategy
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CONCREATESTRATEGYB_H
8: #define CONCREATESTRATEGYB_H
9:
10: #include "Strategy.h"
11: #include <iostream>
12:
13: class ConcreateStrategyB
14: : public Strategy
15: {
16: public:
17: virtual ~ConcreateStrategyB(){}
18: // 算法B实现方法
19: virtual void AlgorithmInterface();
20: };
21:
22: #endif // CONCREATESTRATEGYB_H
1: /************************************************************************
2: * FileName : ConcreateStrategyC.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 具体算法C：封装了具体的算法或行为，继承于Strategy
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CONCREATESTRATEGYC_H
8: #define CONCREATESTRATEGYC_H
9:
10: #include "Strategy.h"
11: #include <iostream>
12:
13: class ConcreateStrategyC
14: : public Strategy
15: {
16: public:
17: virtual ~ConcreateStrategyC(){}
18: // 算法C实现方法
19: virtual void AlgorithmInterface();
20: };
21:
22: #endif // CONCREATESTRATEGYC_H
1: /************************************************************************
2: * FileName : Context.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 上下文类的具体实现
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "Context.h"
8:
9: // 构造时，传入具体的策略对象
10: Context::Context(Strategy *pStrategy)
11: : m_pStrategy(pStrategy)
12: {
13: }
14:
15: Context::~Context()
16: {
17: delete m_pStrategy;
18: m_pStrategy = NULL;
19: }
20:
21: // 根据具体的策略对象，调用其算法的方法
22: void Context::ContextInterface()
23: {
24: if (NULL != m_pStrategy)
25: {
26: m_pStrategy->AlgorithmInterface();
27: }
28: }
1: /************************************************************************
2: * FileName : ConcreateStrategyA.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : ConcreateStrategyA类的具体实现
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "ConcreateStrategyA.h"
8:
9: // 算法A实现方法
10: void ConcreateStrategyA::AlgorithmInterface()
11: {
12: std::cout << "AlgorithmInterface Implemented by ConcreateStrategyA\n";
13: }
1: /************************************************************************
2: * FileName : ConcreateStrategyC.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : ConcreateStrategyC类的具体实现
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "ConcreateStrategyC.h"
8:
9: // 算法C实现方法
10: void ConcreateStrategyC::AlgorithmInterface()
11: {
12: std::cout << "AlgorithmInterface Implemented by ConcreateStrategyC\n";
13: }
1: /************************************************************************
2: * FileName : ConcreateStrategyB.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : ConcreateStrategyB类的具体实现
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "ConcreateStrategyB.h"
8:
9: // 算法B实现方法
10: void ConcreateStrategyB::AlgorithmInterface()
11: {
12: std::cout << "AlgorithmInterface Implemented by ConcreateStrategyB\n";
13: }
1: /************************************************************************
2: * FileName : Main.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : Strategy模式的测试代码
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "Context.h"
8: #include "ConcreateStrategyA.h"
9: #include "ConcreateStrategyB.h"
10: #include "ConcreateStrategyC.h"
11:
12: int main()
13: {
14: Strategy* pStrategy;
15:
16: /**
17: * 由于实例化不同的策略，所以最终在调用实际的算法时，所获得结果就不尽相同
18: */
19: pStrategy = new ConcreateStrategyA();
20: Context* pContext1 = new Context(pStrategy);
21: pContext1->ContextInterface();
22:
23: pStrategy = new ConcreateStrategyB();
24: Context* pContext2 = new Context(pStrategy);
25: pContext2->ContextInterface();
26:
27: pStrategy = new ConcreateStrategyC();
28: Context* pContext3 = new Context(pStrategy);
29: pContext3->ContextInterface();
30:
31: delete pContext1;
32: delete pContext2;
33: delete pContext3;
34:
35: return 0;
36: }
六、实例UML图及源码
（1）纯策略模式
1: /************************************************************************
2: * FileName : CashSuperStratrgy.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 抽象收费算法类：定义所有支持的收费算法的公共接口
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CASHSUPERSTRATEGY_H
8: #define CASHSUPERSTRATEGY_H
9:
10: class CashSuperStrategy
11: {
12: public:
13: CashSuperStrategy() {}
14: virtual ~CashSuperStrategy() {}
15: // 收费算法
16: virtual double AcceptCash(double dMoney) = 0;
17: protected:
18: private:
19: };
20:
21: #endif // CASHSUPERSTRATEGY_H
1: /************************************************************************
2: * FileName : CashContext.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 上下文类，用一个CashConcreateStrategy来配置，维护一个对CashSuperStratrgy对象的引用
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CASHCONTEXT_H
8: #define CASHCONTEXT_H
9: #include "CashSuperStrategy.h"
10: #include <iostream>
11:
12: class CashContext
13: {
14: public:
15: CashContext(CashSuperStrategy *pCashSuperStrategy);//构造时，传入具体的收费策略对象
16: ~CashContext();
17:
18: double GetResult(double dMoney);// 根据具体的收费策略对象，获得具体的计算结果
19: protected:
20: private:
21: CashSuperStrategy* m_pCashSuperStrategy;
22: };
23:
24: #endif // CASHCONTEXT_H
1: /************************************************************************
2: * FileName : CashContext.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : CashContext的具体实现
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "CashContext.h"
8:
9: CashContext::CashContext(CashSuperStrategy * pCashSuperStrategy)
10: {
11: //ctor
12: this->m_pCashSuperStrategy = pCashSuperStrategy;
13: }
14:
15: CashContext::~CashContext()
16: {
17: //dtor
18: delete m_pCashSuperStrategy;
19: m_pCashSuperStrategy = NULL;
20: }
21:
22: double CashContext::GetResult(double dMoney)
23: {
24: return m_pCashSuperStrategy->AcceptCash(dMoney);
25: }
1: /************************************************************************
2: * FileName : CashNormalStrategy.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 具体的正常收费算法类CashNormalStrategy：封装了具体的正常收费算法，继承于Strategy
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CASHNORMALSTRATEGY_H
8: #define CASHNORMALSTRATEGY_H
9:
10: #include "CashSuperStrategy.h"
11:
12:
13: class CashNormalStrategy : public CashSuperStrategy
14: {
15: public:
16: CashNormalStrategy();
17: virtual ~CashNormalStrategy();
18:
19: // 具体的收费算法
20: virtual double AcceptCash(double dMoney);
21: protected:
22: private:
23: };
24:
25: #endif // CASHNORMALSTRATEGY_H
1: /************************************************************************
2: * FileName : CashNormalStrategy.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : CashNormalStrategy的具体实现
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "CashNormalStrategy.h"
8:
9: CashNormalStrategy::CashNormalStrategy()
10: {
11: //ctor
12: }
13:
14: CashNormalStrategy::~CashNormalStrategy()
15: {
16: //dtor
17: }
18:
19: double CashNormalStrategy::AcceptCash(double dMoney)
20: {
21: return dMoney;
22: }
1: /************************************************************************
2: * FileName : CashRebateStrategy.h
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : 具体的打则收费算法类CashNormalStrategy：封装了具体的打折收费算法，继承于Strategy
5: * Time : 2010/5/24
6: ************************************************************************/
7: #ifndef CASHREBATESTRATEGY_H
8: #define CASHREBATESTRATEGY_H
9:
10: #include "CashSuperStrategy.h"
11:
12: class CashRebateStrategy : public CashSuperStrategy
13: {
14: public:
15: CashRebateStrategy(double dMoneyRebate);
16: virtual ~CashRebateStrategy();
17:
18: // 具体的收费算法
19: virtual double AcceptCash(double dMoney);
20: protected:
21: private:
22: double m_dMoneyRebate;
23: };
24:
25: #endif // CASHREBATESTRATEGY_H
1: /************************************************************************
2: * FileName : CashRebateStrategy.cpp
3: * Author : steven oyj (steven.oyj@gmail.com)
4: * Description : CashRebateStrategy的具体实现
5: * Time : 2010/5/24
6: ************************************************************************/
7: #include "CashRebateStrategy.h"
8:
9: CashRebateStrategy::CashRebateStrategy(double dMoneyRebate)
10: {
11: //ctor
12: this->m_dMoneyRebate = dMoneyRebate;
13: }
14:
15: CashRebateStrategy::~CashRebateStrategy()
16: {
17: //dtor
18: }
19:
20: double CashRebateStrategy::AcceptCash(double dMoney)
21: {
22: return dMoney * m_dMoneyRebate;
23: }