装饰设计模式问题？(Decorator design pattern issue?)

 在“头部第一设计模式”一书中，装饰师章节讨论了装饰师处理具体类型并导致问题时的问题。 我正在复制章节中的一些问答： 
 
 问：我有点担心代码可能会测试一个特定的具体组件 - 例如，HouseBlend - 并做一些事情，比如发行折扣。 一旦我用装饰器包装HouseBlend，这就不再适用了。 
 
 答：这是完全正确的。 如果您的代码依赖于具体组件的类型，装饰器将破坏该代码。 只要您只针对抽象组件类型编写代码，装饰器的使用将对您的代码保持透明。 但是，一旦开始编写针对具体组件的代码，您将需要重新考虑应用程序设计和装饰器的使用。 
 
 有人可以给出一个简单的例子，说明'客户'代码是针对具体类型与抽象类型编写的吗？ 前者如何给装饰者带来麻烦？ 
 
 书中装饰器的示例测试代码如下： 
 
public class StarbuzzCoffee {
    public static void main(String args[]) {
        Beverage beverage2 = new DarkRoast();
        beverage2 = new Mocha(beverage2);
        beverage2 = new Mocha(beverage2);
        beverage2 = new Whip(beverage2);
        System.out.println(beverage2.getDescription()
            + “ $” + beverage2.cost());
        ...
    }
}
 
 这个测试代码（也是客户端代码）是针对抽象类型编写的吗？ 
 
 谢谢， 

In book 'Head first design patterns', decorator chapter, it talks about issues when decorator deals with concrete type and cause problems. I am copying some Q&A in the chapter:
 
Q: I’m a little worried about code that might test for a specfic concrete component – say, HouseBlend – and do something, like issue a discount. Once I’ve wrapped the HouseBlend with decorators, this isn’t going to work anymore.
 
A: That is exactly right. If you have code that relies on the concrete component’s type, decorators will break that code. As long as you only write code against the abstract component type, the use of decorators will remain transparent to your code. However, once you start writing code against concrete components, you’ll want to rethink your application design and your use of decorators.
 
Could someone give simple examples on what it means that 'client' code is written against concrete type vs abstract type? And how the former cause trouble for decorator?
 
A sample test code of decorator in the book is like this:
 
public class StarbuzzCoffee {
    public static void main(String args[]) {
        Beverage beverage2 = new DarkRoast();
        beverage2 = new Mocha(beverage2);
        beverage2 = new Mocha(beverage2);
        beverage2 = new Whip(beverage2);
        System.out.println(beverage2.getDescription()
            + “ $” + beverage2.cost());
        ...
    }
}
 
Is this test code(also a client code) written against abstract type?
 
Thanks,

原文：https://stackoverflow.com/questions/12634405