这里描述的许多设计原则有些抽象，因此如果不看实际的代码，可能很难理解它们。找到足够小的示例以包含在书中，但是又足够大以说明真实系统的问题是一个挑战（如果遇到好的示例，请发给我）。因此，这本书可能不足以让您学习如何应用这些原理。
使用本书的最佳方法是与代码审查结合使用。阅读其他人的代码时，请考虑它是否符合此处讨论的概念，以及它与代码的复杂性之间的关系。在别人的代码中比在您的代码中更容易看到设计问题。您可以使用此处描述的红色标记来发现问题并提出改进建议。查看代码还将使您接触到新的设计方法和编程技术。
改善设计技能的最好方法之一就是学会识别危险信号：信号表明一段代码可能比需要的复杂。在本书的过程中，我将指出一些危险信号，这些危险信号指示与每个主要设计问题有关的问题；最重要的内容总结在书的后面。然后，您可以在编码时使用它们：当看到红色标记时，停下来寻找可消除问题的替代设计。当您第一次尝试这种方法时，您可能必须尝试几种设计替代方案，然后才能找到消除危险信号的方案。不要轻易放弃：解决问题之前尝试的替代方法越多，您就会学到更多。随着时间的流逝，您会发现代码中的危险信号越来越少，并且您的设计越来越清晰。
在应用本书中的思想时，务必要节制和谨慎。每条规则都有例外，每条原则都有其局限性。如果您将任何设计创意都发挥到极致，那么您可能会陷入困境。精美的设计反映了相互竞争的思想和方法之间的平衡。有几章的标题为“太过分”，它们描述了如何在做得过大的事情上识别自己。
本书中几乎所有示例都是使用 Java 或 C ++编写的，并且大部分讨论都是针对以面向对象的语言设计类的。但是，这些想法也适用于其他领域。几乎所有与方法有关的思想也可以应用于没有面向对象功能的语言中的功能，例如 C。设计思想还适用于除类之外的模块，例如子系统或网络服务。
在这种背景下，让我们详细讨论导致复杂性的原因以及如何简化软件系统。
Many of the design principles described here are somewhat abstract, so they may be hard to appreciate without looking at actual code. It has been a challenge to find examples that are small enough to include in the book, yet large enough to illustrate problems with real systems (if you encounter good examples, please send them to me). Thus, this book may not be sufficient by itself for you to learn how to apply the principles.
The best way to use this book is in conjunction with code reviews. When you read other people’s code, think about whether it conforms to the concepts discussed here and how that relates to the complexity of the code. It’s easier to see design problems in someone else’s code than your own. You can use the red flags described here to identify problems and suggest improvements. Reviewing code will also expose you to new design approaches and programming techniques.
One of the best ways to improve your design skills is to learn to recognize red flags: signs that a piece of code is probably more complicated than it needs to be. Over the course of this book I will point out red flags that suggest problems related to each major design issue; the most important ones are summarized at the back of the book. You can then use these when you are coding: when you see a red flag, stop and look for an alternate design that eliminates the problem. When you first try this approach, you may have to try several design alternatives before you find one that eliminates the red flag. Don’t give up easily: the more alternatives you try before fixing the problem, the more you will learn. Over time, you will find that your code has fewer and fewer red flags, and your designs are cleaner and cleaner. Your experience will also show you other red flags that you can use to identify design problems (I’d be happy to hear about these).
When applying the ideas from this book, it’s important to use moderation and discretion. Every rule has its exceptions, and every principle has its limits. If you take any design idea to its extreme, you will probably end up in a bad place. Beautiful designs reflect a balance between competing ideas and approaches. Several chapters have sections titled “Taking it too far,” which describe how to recognize when you are overdoing a good thing.
Almost all of the examples in this book are in Java or C++, and much of the discussion is in terms of designing classes in an object-oriented language. However, the ideas apply in other domains as well. Almost all of the ideas related to methods can also be applied to functions in a language without object-oriented features, such as C. The design ideas also apply to modules other than classes, such as subsystems or network services.
With this background, let’s discuss in more detail what causes complexity, and how to make software systems simpler.