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SOLID Principles: The Foundation of Good Code

By Habib Pourfard

Writing code can become messy as your software grows. If you want to keep your projects easy to update and understand, following the SOLID principles is one of the best habits you can build.

SOLID is a set of five simple, powerful ideas for object-oriented programming. These principles help you organise code so that it is clear, flexible, and easy to maintain. Each principle is easy to learn, but together, they make a big difference in how professional your code feels.

Row of tidy school lockers
Think of SOLID like a row of tidy lockers in a school corridor. Each locker has its own job, its own key, and doesn't depend on the others. If you need to move, fix, or clean a locker, you don't need to open all of them—just the one you want.

Real-Life Analogy: School Lockers

Imagine each part of your code is like a locker assigned to a student. Each locker only holds one person's things, is clearly labelled, and can be opened or changed without affecting the rest. This makes it easy to find, use, or fix what you need, without causing problems elsewhere.

  • Each code module has its own clear responsibility, just like a locker has one owner.
  • If you need to make changes, you don't disturb the other lockers.
  • New lockers (code features) can be added without changing the existing ones.

What Are the SOLID Principles?

SOLID is an acronym for five important principles in object-oriented programming:

  • S – Single Responsibility Principle
  • O – Open/Closed Principle
  • L – Liskov Substitution Principle
  • I – Interface Segregation Principle
  • D – Dependency Inversion Principle

Benefits of SOLID

When you follow SOLID, your code becomes much easier to understand and improve. Each piece is designed to do one job, and you can change or expand your software with less risk of breaking things.

  • Improved maintainability and flexibility
  • Fewer bugs when adding new features
  • Code is easier for other developers to read

When Should You Use SOLID?

SOLID is most useful in object-oriented code, especially when projects are growing or teams are collaborating. If you notice your code becoming difficult to change or fix, SOLID is a good place to start.

Final Thoughts

You do not need to use every SOLID principle in every class or project. However, learning and applying them will make you a more confident and productive developer. Your code will be easier to understand, test, and improve.