SOLID Design Principles

Introduction

When creating software, we can follow good practices to avoid issues to make our code easier to understand, robust, and maintainable. Few of these practices are often termed as principles, e.g., the SOLID principles refer to the best practices to be followed in OOD.

SOLID is an acronym for the first five object-oriented design (OOD) principles by Robert C. Martin, also known as Uncle Bob, the author of Clean Code: A Handbook of Agile Software Craftsmanship.

The illustration below represents the acronym for SOLID design principles.

Why use SOLID principles?

Let’s look at the possible issues below that may occur in the code if we don’t adhere to the SOLID principles.

• The code may become tightly coupled with several components, which makes it difficult to integrate new features or bug fixes and sometimes leads to unidentified problems.
• The code will be untestable, which effectively means that every change will need end-to-end testing.
• The code may have a lot of duplication.
• Fixing one issue results in additional errors.

However, if we adhere to the SOLID principles, we are able to do the following:

• Reduce the tight coupling of the code, which reduces errors.
• Reduce the code’s complexity for future use.
• Produce more extensible, maintainable, and understandable software code.
• Produce the code that is modular, feature specific, and is extremely testable.

Design principles

Let’s look at the definition of the five design principles.

• In the Single Responsibility Principle (SRP), each class should be responsible for a single part or functionality of the system.
• In the Open Closed principle (OCP), software components should be open for extension but closed for modification.
• In the Liskov Substitution Principle (LSP), objects of a superclass should be replaceable with objects of its subclasses without breaking the system.
• The Interface Segregation Principle (ISP) makes fine-grained interfaces that are client specific.
• The Dependency Inversion Principle (DIP), ensures that the high-level modules are not dependent on low-level modules. In other words, one should depend upon abstraction and not concretion.