本章开篇综述：
1. A component is a logical, replaceable part of a system that conforms to and provides the realization of a set of interfaces.
组件的目的是通过可替换的方法，实现相同的接口，构建灵活的系统。
2. Good components define crisp abstractions with well-defined interfaces, making it possible to easily replace older components with newer, compatible ones. 这句话是扯淡，地球人都知道。
3. Interfaces bridge your logical and design models. For example, you may specify an interface for a class in a logical model, and that same interface will carry over to some design component that realizes it.
分析问题时，脑海中先形成逻辑模型，抽象出接口，然后留到设计组件时实现。（想想，共鸣中...）
4. Interfaces allow you to build the implementation of a component using smaller components by wiring ports on the components together.
组件和组件可以组合。灵活的构建复用的组件是必须的。
