SOLID

SOLID Principles Recap

A refresher on the five SOLID object-oriented design principles and how they form the underlying rationale for many Gang of Four design patterns.

SOLID Principles Overview

A guided tour of the five SOLID design principles that make object-oriented code easier to maintain and extend.

What is Coupling and Cohesion in OOP?

Coupling measures how dependent one module or class is on another, while cohesion measures how strongly the responsibilities inside a single module belong toge…

What is the Liskov Substitution Principle?

The Liskov Substitution Principle (LSP) states that objects of a subclass must be substitutable for objects of the base class without altering the correctness…

What is the Open-Closed Principle?

The Open-Closed Principle (OCP) states that software entities — classes, modules, functions — should be open for extension but closed for modification, meaning…

What is the Interface Segregation Principle?

The Interface Segregation Principle (the 'I' in SOLID) states that no client should be forced to depend on methods it does not use, so large interfaces should…

What is the Dependency Inversion Principle?

The Dependency Inversion Principle (the 'D' in SOLID) states that high-level modules should not depend on low-level modules — both should depend on abstraction…

Liskov Substitution Violation: A Concrete Example

A classic Liskov Substitution Principle violation is a Square class extending a Rectangle class: because setting a Square’s width must also change its height (…

What is a Fat Interface in OOP?

A fat interface is an interface that declares too many unrelated methods, forcing implementing classes to provide (or stub out) behavior they don’t actually ne…

What is Interface Pollution in OOP?

Interface pollution is the ongoing design mistake of adding methods to an existing shared interface that are only relevant to some implementers, gradually turn…

What is a Role Interface in OOP?

A role interface is a small, focused interface that describes one specific behavior or capability a client depends on, rather than the full public surface of a…