<<interface>>VipStrategy
+ isAvailable()+ payoff()
DefaultDiscountStrategy
SilverStrategy
GoldenStrategy
1
<<interface>>DiscountStrategy
*
NotDiscountStrategy
PaymentBus
+ discountStrategies+ vipStrategies+ vipBus
+ payoff()
ClassifyDiscountStrategy
简单软件
TimeLimitedDiscStrategy
VipBus
+ isAvailable()+ welfare()+ privilege()
复杂软件
QuantityLimitedDiscStrategy
