最初版本

enum TaxBase
{CN_Tax,US_Tax,DE_Tax
};class SalesOrder
{TaxBase tax;
public:double CalcaulateTax(){if (tax == CN_Tax){}else if (tax == US_Tax){}else if (tax == DE_Tax){}}
};

最终版本

class TaxStrategy
{
public:virtual double Calculate(const Context& contxt) = 0;virtual	~TaxStrategy(){}
};class CNTax : public TaxStrategy
{
public:virtual double Calculate(const Context& contxt){}
};class USTax : public TaxStrategy
{
public:virtual double Calculate(const Context& contxt){}
};class DETax : public TaxStrategy
{
public:virtual double Calculate(const Context& contxt){}
};class SaleOrder
{
private:TaxStrategy* strategy;
public:SaleOrder(StrategyFactory* strategyfactory){strategy = strategyfactory->NewStrategy;}~SaleOrder(){delete strategy;}double CalculateTax(){Context context;double val = strategy->Calculate();}
};