Introduction to SOLID Principles in Object-Oriented Design

Do you know what SOLID (not “solid,” but S.O.L.I.D) object-oriented design stands for? It stands for: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion.

This acronym was coined by Robert C. Martin (also known as Uncle Bob). According to him, these principles form the backbone of robust object-oriented design. You can read more about these principles in his book, "Agile Software Development: Principles, Patterns, and Practices". I will describe these principles in detail in following posts, of course, in a timely manner. :)

Before diving into the SOLID principles, it’s helpful to understand the negative characteristics of poor object-oriented design that these principles aim to mitigate. Robert C. Martin outlines these “bad smells” in design as:

• Rigidity: The system is difficult to change because a single modification affects too many other parts.
• Fragility: When a change is made, unexpected parts of the system break.
• Immobility: Components are hard to reuse in another application because they are too tightly coupled to the current application.