What is SOLID?

SOLID is a set of five principles of object-oriented programming aimed at creating flexible, extendable, and maintainable systems. Each principle helps avoid common problems in code design:

• S (Single Responsibility Principle) — A class should have only one reason to change.
• O (Open/Closed Principle) — Software entities should be open for extension but closed for modification.
• L (Liskov Substitution Principle) — Subtypes must be substitutable for their base types without altering the correctness of the program.
• I (Interface Segregation Principle) — Clients should not be forced to depend on interfaces they do not use.
• D (Dependency Inversion Principle) — High-level modules should not depend on low-level modules; both should depend on abstractions.

Example in C# for the Single Responsibility Principle:

class ReportGenerator
{
    public string GenerateReport() {
        // report generation logic
    }
}

class ReportPrinter
{
    public void Print(string report) {
        // report printing logic
    }
}

Here, report generation and printing are separated into different classes, which complies with SRP.