Software Architect's Handbook

Liskov Substitution Principle (LSP)

Inheritance is one of the four pillars of object-oriented programming (OOP). It allows subclasses to inherit from a base class (sometimes referred to as the parent class), which includes the properties and methods of the base class. When you first learned about inheritance, you may have been taught about "is a" relationships. For example, "Car is a Vehicle," if Car was a base class and Vehicle was a subtype of that base class.

The Liskov Substitution Principle (LSP) is an object-oriented principle that states that subtypes must be substitutable for their base types without having to alter the base type. If a subtype is inherited from a base class, we should be able to substitute the subclass for that base ...