Chapter 3. The Purpose of Design Patterns

Visitor, Strategy, Decorator. These are all names of design patterns that we’ll deal with in the upcoming chapters. However, before taking a detailed look at each of these design patterns, I should give you an idea about the general purpose of a design pattern. Thus in this chapter, we will first take a look at the fundamental properties of design patterns, why you would want to know about them and use them.

In “Guideline 1: Understand the Importance of Software Design, I already used the term design pattern and explained on which level of software development you use them. However, I have not yet explained in detail what a design pattern is. That will be the topic of “Guideline 11: Understand the Purpose of Design Patterns”: you will understand that a design pattern has a name that expresses an intent, introduces an abstraction that helps to decouple software entities, and has been proven over the years.

In “Guideline 12: Beware of Design Pattern Misconceptions”, I will focus on several misconceptions about design patterns and explain what a design pattern is not. I will try to convince you that design patterns are not about implementation details and do not represent language-specific solutions to common problems. I will also do my best to show you that they are not limited to object-oriented programming nor to dynamic polymorphism.

In “Guideline 13: Design Patterns Are Everywhere”, I will demonstrate that it’s hard to avoid design ...

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