Dependency Inversion Principle
In this article, we will see the Dependency Inversion Principle (DIP), which is the “D” in the SOLID principles.
“The Dependency Inversion Principle (DIP) states that High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstraction..” — Uncle Bob Martin, Agile Software Development: Principles, Patterns, and Practices
Dependency Inversion Principle is about two concepts: decoupling and modularization.
Let me explain more …
When I started writing Java Swing apps in 2010 I had used to create classes and instantiate them inside the classes that used them. So they depended directly on those implementation details.
Today we consider decoupling and polymorphism, so we use interfaces to make our dependencies clear. This is called the Dependency Injection (DI) or Inversion of Control (IoC), and it is not Dependency Inversion Principle.
Inversion of Control is a principle by which the control of objects is transferred to a container, means instead of creating an object using the new operator, let a generic container do that for you.
Dependency injection is a technique through which to implement IoC for resolving dependencies, where implementation objects are passed into another object to behave correctly.
Closely linked to the DIP are the DI and the IoC, they all work great together. So to be clear…
The Dependency Inversion Principle is all about separating your classes from concrete implementations and having them depend on abstract classes or interfaces.
The “lower-level” implementations are dependent on the interfaces owned by the “higher level” implementations.
This promotes the mantra of coding to an interface rather than an implementation. By applying this, the flexibility increases in the system, and it ensures that some specific component is not tightly coupled to one implementation.
Example: Let say you want to switch on a broken door in a room. You don’t have to break the existent door frame and cause a “bordel”. The work is done before, so all you have to do is to buy a door that fits in the frame because its dimensions are standard. Doors are built based on these dimensions which represent the interface.
class Room constructor() door = new Door(200, 60) end end
class Room constructor(newDoor) door = newDoor end end
In this tutorial, we’ve learned what is DIP and I hope you understood what DIP is and made you aware of its traits.