Liskov’s Substitution Principle

The principle was introduced by Barbara Liskov in 1987 and according to this principle “Derived or child classes must be substitutable for their base or parent classes“. This principle ensures that any class that is the child of a parent class should be usable in place of its parent without any unexpected behavior.

Let’s understand Liskov’s Substitution Principle using an example:

One of the classic examples of this principle is a rectangle having four sides. A rectangle’s height can be any value and width can be any value. A square is a rectangle with equal width and height. So we can say that we can extend the properties of the rectangle class into square class.

In order to do that you need to swap the child (square) class with parent (rectangle) class to fit the definition of a square having four equal sides but a derived class does not affect the behavior of the parent class so if you will do that it will violate the Liskov Substitution Principle.

In software development, Object-Oriented Design plays a crucial role when it comes to writing flexible, scalable, maintainable, and reusable code. There are so many benefits of using OOD but every developer should also know the SOLID principle for good object-oriented design in programming. The SOLID principle was introduced by Robert C. Martin, also known as Uncle Bob and it is a coding standard in programming. This principle is an acronym of the five principles which are given below:

• Single Responsibility Principle (SRP)
• Open/Closed Principle
• Liskov’s Substitution Principle (LSP)
• Interface Segregation Principle (ISP)
• Dependency Inversion Principle (DIP)

The SOLID principle helps in reducing tight coupling. Tight coupling means a group of classes are highly dependent on one another which you should avoid in your code.

• Opposite of tight coupling is loose coupling and your code is considered as a good code when it has loosely-coupled classes.
• Loosely coupled classes minimize changes in your code, helps in making code more reusable, maintainable, flexible and stable. Now let’s discuss one by one these principles…