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SOLID Principles

SRP, OCP, LSP, ISP, DIP with practical examples

5 sections

Start: Interface Segregation Principle (ISP)

Foundational 3

  1. Interface Segregation Principle (ISP)The Interface Segregation Principle says clients should never be forced to depend on methods they don't use. Splitting a fat contract into focused, role-based interfaces keeps implementations honest, shrinks the surface that mocks and…, not read
  2. Open Closed Principle (OCP)The Open/Closed Principle says modules should be open for extension but closed for modification: new behaviour should arrive as new types (strategies, plugins, decorators) rather than edits to battle-tested code. Done well it eliminates…, not read
  3. Single Responsibility Principle (SRP)The Single Responsibility Principle says a class should have exactly one reason to change. Keeping responsibilities like validation, execution, and logging in separate classes shrinks the blast radius of every edit, makes tests…, not read

Mid-level 2

  1. Dependency Inversion Principle (DIP)The Dependency Inversion Principle flips the normal flow: high-level policy and low-level details both depend on abstractions, not the other way round. Injecting interfaces through constructors (wired at the composition root) decouples…, not read
  2. Liskov Substitution Principle (LSP)The Liskov Substitution Principle states that any subclass must be usable wherever its base type is expected, without surprises. When derived types throw NotSupportedException, strengthen preconditions, or weaken postconditions, callers…, not read