为什么我们需要装饰器模式中的抽象装饰器类？答案

【问题标题】：Why we need abstract decorator class in Decorator Pattern?为什么我们需要装饰器模式中的抽象装饰器类？
【发布时间】：2019-01-18 19:22:29
【问题描述】：

在Decorator Pattern，如果我

移除装饰器继承的抽象装饰器类和
有decorators直接继承decoratee的接口。

输出是一样的。

我的问题是为什么还要添加额外的abstractor class 来制作装饰器？

例如：

标准decorator pattern的Scala源代码在这里：https://gist.github.com/kencoba/1875983

虽然我遵循上述步骤的版本如下：（通过删除抽象装饰器类（CoffeeDecorator 这里）并让装饰器直接继承被装饰者（Coffee 这里））

trait Coffee {
  def cost: Double
  def ingredients: String
}

//abstract class CoffeeDecorator(decoratedCoffee: Coffee) extends Coffee {
//  val sep = ", "
//
//  override def cost = decoratedCoffee.cost
//  override def ingredients = decoratedCoffee.ingredients
//}

class Milk(decoratedCoffee: Coffee) extends Coffee {
  override def cost = decoratedCoffee.cost + 0.5
  override def ingredients = decoratedCoffee.ingredients + "," + "Milk"
}

class Whip(decoratedCoffee: Coffee) extends Coffee {
  override def cost = decoratedCoffee.cost + 0.7
  override def ingredients = decoratedCoffee.ingredients + "," + "Whip"
}


object DecoratorSample {... // same as the comparing source code.

【问题讨论】：

标签： java scala design-patterns decorator

【解决方案1】：

在摆弄之后，我发现了不同之处。该抽象装饰器提供了默认的覆盖，因此在某些情况下，它可以减少装饰器实现的类型，因为我们并不总是装饰所有方法并提供通用帮助器。

trait Coffee {
  def cost: Double
  def ingredients: String
}

class FreeMilk(decoratedCoffee: Coffee) extends Coffee {
  // this is a waste of line
  override def cost = decoratedCoffee.cost 
  override def ingredients = decoratedCoffee.ingredients + "," + "Milk"
}

abstract class CoffeeDecorator(decoratedCoffee: Coffee) extends Coffee {
  val sep = ", "
  override def cost = decoratedCoffee.cost
  override def ingredients = decoratedCoffee.ingredients
}
class FreeMilk2(decoratedCoffee: Coffee) extends CoffeeDecorator(decoratedCoffee) {
  // less typings and give you some base helpers
  override def ingredients = super.ingredients + sep + "Milk"
}

【讨论】：