Design Principle: SOLID Principles

Summary

Principle Name	SOLID Principles
Acronym	SOLID
Principle Type	OOP Design Principle
Purpose	To make code more maintainable, flexible, and easily understandable.
Related Principles	Single Responsibility Principle(SRP) Open/Closed Principle(OCP) Liskov Substitution Principle(LSP) Interface Segregation Principle(ISP) Dependency Inversion Principle(DIP)

Definition

SOLID principles are a collection of design principles used to make the implementation of software systems more readable, maintainable, flexible(for later changes), and easily understandable.

SOLID Principles refer to a collection of five(5) individual principles, widely used in Object-Oriented Programming(OOP).

The term “SOLID” is derived from the first letter of each of those 5 principles.

The SOLID design principles are five(5) ideas that can help us build a software system that is easy to adapt and extend.

Here are the file(5) principles-

– Single Responsibility Principle(SRP)

– Open/Closed Principle(OCP)

– Liskov Substitution Principle(LSP)

– Interface Segregation Principle(ISP)

– Dependency Inversion Principle(DIP)

What SOLID Principles are

OOP Design Guideline: SOLID principles provide guidelines and best practices for writing and structuring classes, methods, and defining relationships.

Clean Code: these principles promote readable, maintainable, and modular clean code.

Loose Coupling: these principles promote loose coupling and minimum direct dependency.

Design Pattern Foundation: SOLID principles work as functions for implementing different design patterns.

High Testability: these principles enable us to write unit tests easily, because of loose coupling, and dependency inversion.

High Extensible: code written following these principles is highly extensible, and ready to adopt future changes without affecting the existing implementations.

What SOLID Principles are not

Not Strict Rules: these principles are not very strict rules, but just some recommendations.

Not Design Patterns: these principles are not design patterns, these are just guidelines.

Not a Framework: these principles are not a framework or package or library.

Not Performance or Security Related: SOLID principles are not related to code performance, security, deployment, licensing, resource optimization/management.

Details of SOLID Principles

We have discussed each of the five(5) principles of SOLID Principles separately, in individual articles. In those separate articles, we are digging deep into each principle and going to very detailed explanation of those principles.

Read the principles in detail using the following links-

Principle	Acronym	Purpose/Tagline
Single Responsibility Principle	SRP	A class should do one thing and do it well.
Open/Closed Principle	OCP	Software entities should be open for extension, but closed for modification.
Liskov Substitution Principle	LSP	Objects of superclass should be replaceable with the objects of the subclass without affecting the correctness.
Interface Segregation Principle	ISP	A class should not be forced to implement interfaces that it does not use.
Dependency Inversion Principle	DIP	High-level modules should not depend on low-level modules, rather both should depend on abstractions.

Advantages of SOLID

Following and implementing SOLID principles have a huge impact on the source code. These principles contribute to the quality and longevity of the software system project.

Here are a few key advantages we get from SOLID Principles-

Modularity: divide code into small, independent, and reusable modules.

Maintainability: codebase becomes easy to update and manage, as SOLID principles give it a recognizable pattern.

Code Duplication Reduction: reduce code duplication, also reduc redundant logic implementation.

Easy Debugging: debugging becomes easier because of modularity and predictable patterns.

Improved Readability: clear structure and separation of code and logic make it more readable.

Easy Understandability: recognizable patterns make the code easily understandable.

Enhanced Testability: testing becomes easier because of smaller and loosely coupled components.

Improved Change Adaptability: changes can be adapted easily because of smaller components and abstractions.

Usage in Design Pattern

SOLID Principles are heavily used in the implementation of design patterns, providing the structure and flexibility needed for clean, maintainable code.

Here is a list of design patterns that use one or more of the SOLID Principles.

Design Pattern	Related SOLID Principle(s)	Explanation
Singleton Pattern	Single Responsibility Principle (SRP)	Ensures that a class has only one responsibility while controlling the creation of its singleton instance.
Factory Method Pattern	Open/Closed Principle (OCP)	Allows for object creation to be extended by introducing new classes, without modifying the factory itself.
Abstract Factory Pattern	Dependency Inversion Principle (DIP)	Uses abstract interfaces for creating families of related objects, decoupling high-level modules from low-level concrete classes.
Builder Pattern	Single Responsibility Principle (SRP)	Separates the construction of a complex object from its representation, giving the builder one clear responsibility.
Prototype Pattern	Liskov Substitution Principle (LSP)	Subclasses of a prototype class can be substituted without affecting functionality, supporting LSP.
Adapter Pattern	Open/Closed Principle (OCP) Liskov Substitution Principle (LSP)	The Adapter class can introduce new behaviors without modifying existing code (OCP) and follows LSP by ensuring the adapted interface can substitute its original.
Decorator Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP)	Extends functionality of objects without modifying their code (OCP), while adhering to SRP by separating concerns.
Strategy Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP)	Encapsulates interchangeable algorithms, allowing behavior to be extended without altering the context class (OCP), while keeping algorithm implementations separated (SRP).
Observer Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP)	Separates notification logic from business logic (SRP) and allows observers to be added/removed without changing the observable (OCP).
Composite Pattern	Liskov Substitution Principle (LSP)	Ensures that individual objects and composites can be used interchangeably, following the LSP.
Command Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP)	Commands encapsulate actions, allowing new commands to be added without modifying existing code (OCP) while each command has a single responsibility (SRP).
Facade Pattern	Single Responsibility Principle (SRP)	Simplifies the interface of complex subsystems, providing a single, more focused responsibility for client interactions.
Mediator Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP)	The Mediator centralizes communication between components, adhering to SRP, and new interactions can be introduced without modifying existing code (OCP).
State Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP)	The state pattern separates behavior based on state, adhering to SRP, and allows adding new states without altering existing classes (OCP).
Template Method Pattern	Open/Closed Principle (OCP) Liskov Substitution Principle (LSP)	Subclasses can override steps of the algorithm without changing the overall structure (LSP), and the template method allows extending the algorithm without modification (OCP).
Chain of Responsibility Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP)	Each handler in the chain has one responsibility (SRP), and new handlers can be added without modifying existing ones (OCP).
Visitor Pattern	Single Responsibility Principle (SRP) Open/Closed Principle (OCP) Liskov Substitution Principle (LSP)	Visitor lets you add new operations to a class hierarchy without altering the hierarchy itself (OCP), each visitor class has a single responsibility (SRP), and visitors can operate on objects in a consistent way (LSP).