做一个咖啡店的订单系统。
买咖啡时,可以要求加入各种调料,如奶,豆浆,摩卡等。咖啡店会根据调料的不同收取不同的费用。订单系统要考虑这些。
然后下面就是所有的咖啡....:
cost方法将计算出咖啡加上各种调料后的价格。
这种方法太笨了。。。必须换一种。
使用实例变量和继承!
但是有新的问题:
1.调料价格变化就需要更改现有的代码。
2.一旦出现新的调料,就需要加上新的方法,并改变超类中的cost方法。
3.如果有新的饮料,有些调料可能会不适用。
4.想买双倍的摩卡咖啡怎么办?
类应该对扩展开发,对修改关闭。
装饰者模式动态的将责任附加到对象上。若要扩展功能,装饰者提供了比继承更有弹性的替代方案。
Beverage:
namespace C03DecoratorPattern.Bases
{
public abstract class Beverage
{
protected string Description;
protected Beverage()
{
Description = "Unknown Beverage";
}
public abstract double Cost();
public virtual string GetDescription()
{
return Description;
}
}
}
CondimentDecorator:
namespace C03DecoratorPattern.Bases
{
public abstract class CondimentDecorator : Beverage
{
public abstract override double Cost();
public abstract override string GetDescription();
}
}
咖啡们:
namespace C03DecoratorPattern.Beverages
{
public class Espresso : Beverage
{
public Espresso()
{
Description = "Espresso";
}
public override double Cost()
{
return 1.99;
}
}
}
namespace C03DecoratorPattern.Beverages
{
public class HouseBlend : Beverage
{
public HouseBlend()
{
Description = "House Blend Coffee";
}
public override double Cost()
{
return .89;
}
}
}
调料们:
namespace C03DecoratorPattern.Condiments
{
public class Milk : CondimentDecorator
{
private readonly Beverage _beverage;
public Milk(Beverage beverage)
{
_beverage = beverage;
}
public override double Cost()
{
return .34 + _beverage.Cost();
}
public override string GetDescription()
{
return $"{_beverage.GetDescription()}, Milk";
}
}
}
namespace C03DecoratorPattern.Condiments
{
public class Mocha : CondimentDecorator
{
private readonly Beverage _beverage;
public Mocha(Beverage beverage)
{
_beverage = beverage;
}
public override double Cost()
{
return .2 + _beverage.Cost();
}
public override string GetDescription()
{
return $"{_beverage.GetDescription()}, Mocha";
}
}
}
namespace C03DecoratorPattern.Condiments
{
public class Soy: CondimentDecorator
{
private readonly Beverage _beverage;
public Soy(Beverage beverage)
{
_beverage = beverage;
}
public override double Cost()
{
return .17 + _beverage.Cost();
}
public override string GetDescription()
{
return $"{_beverage.GetDescription()}, Soy";
}
}
}
测试程序:
namespace C03DecoratorPattern
{
class Program
{
static void Main(string[] args)
{
Beverage beverage = new Espresso();
Console.WriteLine($"{beverage.GetDescription()} $ {beverage.Cost()}");
Beverage beverage2 = new HouseBlend();
beverage2 = new Mocha(beverage2);
beverage2 = new Milk(beverage2);
beverage2 = new Soy(beverage2);
Console.WriteLine($"{beverage2.GetDescription()} $ {beverage2.Cost()}");
Console.ReadLine();
}
}
}
运行结果: