18 Mar 2023

What are SOLID Principles, and do they really make a difference?

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Written by Balaji Masal

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When it comes to software development, object-oriented (OO) programming is a key concept that brought a whole new design to the process of developing software. It enables developers to combine data with the same functionality in one class to manage with the sole purpose there, without worrying about the entire application.

However, it does not ensure completely maintainable and flexible programs; this is where SOLID principles come in.

Introduced by Robert C. Martin in 2000, the concept of SOLID principles was later built upon by Michael Feathers, who first introduced the SOLID acronym. The last two decades have seen a phenomenal evolution of these principles, making them an integral part of object-oriented programming.

The SOLID principle now serves as a framework to focus specifically on the quality of object-oriented programming and make fine arguments for things such as how software code should be split up, how code should use other code, which parts should be internal or exposed, and more.

This blog aims to explore more about these principles, what they mean and what difference they make.

What is the Importance of Good Design Principles, and Where Does SOLID Fit? 

The importance of good software design principles in a software development life cycle is immense. They are of significant help to developers and allow them to make requisite changes while also giving their best without disrupting the software’s working features.

In simpler terms, this means that well-structured software design principles offer excellent means to handle the complexity of the design process in a more efficient manner. Managing such design complexity effectively has the dual benefit of reducing the efforts required for design along with eliminating the chances of introducing errors during software design.

SOLID is one design principle that acts as a proven rubric for creating quality software. Apart from allowing developers to build understandable and flexible software, it also makes it easy to create readable and testable code.

Understanding SOLID Principles in Detail

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The SOLID principle is made up of five different concepts of object-oriented programming. These are:

  • Single Responsibility
  • Open/Closed
  • Liskov Substitution
  • Interface Segregation
  • Dependency Inversion 

Let’s discuss each one of these principles in detail here.

Single Responsibility

As per this principle of the SOLID framework, each object class (specific methods, parameters, and variables) added to a codebase should manage or be responsible for just one specific job or function.

Put simply, it is recommended that a capability (service, module, or API) have no more than one purpose.


As per this principle, developers can add various new features to a codebase without disturbing the existing code. This means that extending a system’s behaviour is preferable to changing it.

This principle helps separate the existing code from the modified mode to offer better stability and maintainability and minimize code changes.

Liskov Substitution Principle

This is the principle that ensures that any class that is the derived class should be usable in place of its parent class without any unexpected behaviour.

It helps developers avoid unpredictable consequences of changes and having to open a closed class in order to make changes.

Interface Segregation Principle

As per this principle, clients should have fine-grained contracts or interfaces so that calls aren’t entirely dependent on the functionality they aren’t using.

This principle aligns with the Single Responsibility principle in that when we break apart interfaces, we essentially promote composition through role separation.

Dependency Inversion Principle 

The principle states that there shouldn’t be any dependency between high-level and low-level modules, and both should be abstraction-based.

Essentially, this concept of interface abstraction is applied to software components and layers at the higher and lower levels, thus helping to remove the dependencies between them.

To Conclude

The overall objective of SOLID principles is to lessen the code dependencies so that adding new features or changing a part of the code doesn’t necessarily alter/break the whole build. Applying SOLID principles to object-oriented design makes the code easier to manage, understand, maintain, and change as well.

In a nutshell, it is best to keep these principles in mind when writing code as they make it easier for developers and other stakeholders to collaborate on your project by simplifying the process of extending, testing, modifying, and refactoring the code.

Eponymous to its acronym, SOLID principles, indeed have a solid impact in designing a good application. Similarly, over the years, we have come to discover that redefining the QA approach can help add tremendous value to the end user. Infact, Vrushali Majithia, Senior QA, and Project Management expert at IncubXperts, has penned down her take on this very approach. Read here – How a Redefined QA Approach Can Add Value to Your Business