SOLID Liskov Substitution Principle: What is it and how does it work?

Published: 01 January 1970
on channel: Cameron McKenzie

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The Liskov Substitution Principle (LSP) is one of the five SOLID principles of object-oriented design, which are a set of guidelines aimed at making software designs more understandable, flexible, and maintainable.

Liskov Substitution Principle (LSP)

The Liskov Substitution Principle states that objects of a superclass should be replaceable with objects of a subclass without affecting the correctness of the program. In essence, a subclass should behave in such a way that it can stand in for its superclass without causing any errors or unexpected behavior.

Relation to SOLID

LSP is the "L" in the SOLID acronym. SOLID principles, introduced by Robert C. Martin, are a collection of five design principles intended to make software more robust and maintainable. LSP specifically ensures that inheritance and polymorphism are used correctly in object-oriented design.

The Other SOLID Principles

1. Single Responsibility Principle (SRP):
A class should have only one reason to change, meaning it should only have one job or responsibility. This makes the class easier to understand, maintain, and test.

2. Open/Closed Principle (OCP):
Software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. This means that the behavior of a module can be extended without modifying its source code.

3. Liskov Substitution Principle (LSP):
Objects of a superclass should be replaceable with objects of a subclass without affecting the correctness of the program. Subclasses should adhere to the behavior expected by the superclass.

4. Interface Segregation Principle (ISP):
Clients should not be forced to depend on interfaces they do not use. This means creating specific, small interfaces instead of a large, general-purpose one.

5. Dependency Inversion Principle (DIP):
High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions. This principle aims to decouple software modules to make the system more flexible and easier to maintain.

Summary

SRP: One class, one responsibility.
OCP: Open for extension, closed for modification.
LSP: Subclasses should replace superclasses without altering the program's correctness.
ISP: Prefer many small, specific interfaces over a single, large interface.
DIP: Depend on abstractions, not concrete implementations.

Together, these principles aim to create systems that are modular, scalable, and easy to maintain.

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