Conclusion

Traditional procedural programming creates a dependency structure in which policy depends on detail. This is unfortunate, since the policies are then vulnerable to changes in the details. Object-oriented programming inverts that dependency structure such that both details and policies depend on abstraction, and service interfaces are often owned by their clients.

Indeed, this inversion of dependencies is the hallmark of good object-oriented design. It doesn't matter what language a program is written in. If its dependencies are inverted, it has an OO design. If its dependencies are not inverted, it has a procedural design.

The principle of dependency inversion is the fundamental low-level mechanism behind many of the benefits claimed for object-oriented technology. Its proper application is necessary for the creation of reusable frameworks. It is also critically important for the construction of code that is resilient to change. Since abstractions and details are isolated from each other, the code is much easier to maintain.