SOLID

Introduction

SOLID is an acronym for the first five object-oriented design (OOD) principles by Robert C. Martin (also known as Uncle Bob).

These principles establish practices that lend to developing software with considerations for maintaining and extending as the project grows. Adopting these practices can also contribute to avoiding code smells, refactoring code, and Agile or Adaptive software development.

SOLID stands for:

• S - Single-responsiblity Principle
• O - Open-closed Principle
• L - Liskov Substitution Principle
• I - Interface Segregation Principle
• D - Dependency Inversion Principle

In this article, you will be introduced to each principle individually to understand how SOLID can help make you a better developer.

Single-Responsibility Principle

Single-responsibility Principle (SRP) states:

A class should have one and only one reason to change, meaning that a class should have only one job.

That satisfies the single-responsibility principle.

Open-Closed Principle

Open-closed Principle (OCP) states:

Objects or entities should be open for extension but closed for modification.

This means that a class should be extendable without modifying the class itself.

Liskov Substitution Principle

Liskov Substitution Principle states:

Let q(x) be a property provable about objects of x of type T. Then q(y) should be provable for objects y of type S where S is a subtype of T.

This means that every subclass or derived class should be substitutable for their base or parent class.

Interface Segregation Principle

Interface segregation principle states:

A client should never be forced to implement an interface that it doesn’t use, or clients shouldn’t be forced to depend on methods they do not use.

Dependency Inversion Principle

Dependency inversion principle states:

Entities must depend on abstractions, not on concretions. It states that the high-level module must not depend on the low-level module, but they should depend on abstractions.