Introduction 介绍

We have reached our final destination in our overview of the five SOLID design principles! The final principle is the Dependency Inversion principle, and it states that high-level code should not depend on low-level code. Instead, high-level code should depend on an abstraction layer that serves as a "middle-man" between the high and low-level code. A second aspect to the principle is that abstractions should not depend upon details, but rather details should depend upon abstractions. If this all sounds extremely confused, don't worry. We'll cover both aspects of this principle below.

在整个“坚实”原则概述的旅途中，我们到达最后一站了！最后的原则是依赖反转原则，它规定高等级的代码不应该依赖低等级的代码。首先，高等级的代码应该依赖着抽象层，抽象层就像是“中间人”一样，负责连接着高等级和低等级的代码。其次，抽象定义不应该依赖着具体实现，但具体实现应该依赖着抽象定义。如果这些东西让你极端困惑，别担心。接下来我们会将这两方面统统介绍给你。

Dependency Inversion Principle 依赖反转原则

This principle states that high-level code should not depend on low-level code, and that abstractions should not depend upon details.

该原则要求高等级代码不应该依赖低等级代码，抽象定义不应该依赖具体实现。