Liskov Substitution Principle (LSP)

Not all IS-A relationships should be modeled with Inheritance

Example: Square inherits from Rectangle

• When we perform the change width operation on both objects → Square will change its length, while Rectangle doesn’t.
  • When we perform obtain length operation. Square will return its changed length, while Rectangle returns unchanged length → this violates OOP Compatibility

Fix: use a common interface

• Abstract the Square & Rectangle properties into an interface, implement the width & length in the each of the class → so we aren’t able to substitute object on the obtain length(Only available to the Reactangle object), thus ensuring OOP Compatibility

Preventing Inheritance and Method Overriding

• Make it easier to argue for the correctness of programs
• We can make the Class Final or the individual Methods Final
• java.lang.Math & java.lang.String cannot be inherited

Unit Testing

• Test cases based on expected inputs and resulted outputs
• After substituting the parent Network Object with child Network Object, we are expecting the unit test cases return the same output. Otherwise, Liskov Substitution Principle (LSP) is violated
• Example

Ensire Liskov Substitution Principle (LSP) during Compile Time

• Use of Assert