C H A P T E R  10

Object-Oriented Design Principles

Devotion to the facts will always give the pleasures of recognition; adherence to the rules of design, the pleasures of order and certainty.

—Kenneth Clark

How can I qualify my faith in the inviolability of the design principles? Their virtue is demonstrated. They work.

—Edgar Whitney

Now that we’ve spent some time looking at object-oriented analysis and design, let's recapitulate some of what we’ve already seen and add some more pithy prose. First, let's talk about some common design characteristics.

First, designs have a purpose. They describe how something will work in a context, using the requirements (lists of features, user stories, and use cases) to define the context. Second, designs must have enough information in them so that someone can implement them. You need enough details in the design so that someone can come after you and implement the program correctly. Next, there are different styles of design, just like there are different types of house architectures. The type of design you want depends on what it is you’re being required to build. It depends on the context (see, we’re back to context); if you’re an architect, you’ll design a different kind of house at the sea shore than you will in the mountains. Finally, designs ....