OOP concept Interface VS Abstract class in php

 What is the key difference between Interface and Abstract Class

The key difference lies in purpose and approach of their usage. 

1. Key Differences Between Interface and Abstract Class

Feature	Interface	Abstract Class
Method Implementation	Only method signatures (no implementation)	Can have both abstract and concrete (implemented) methods
Properties	Cannot have properties (variables)	Can have properties (variables)
Constructor	Cannot have a constructor	Can have a constructor
Multiple Inheritance	A class can implement multiple interfaces	A class can extend only one abstract class
Access Modifiers	All methods must be public	Methods can have public, protected, or private visibility
Use Case	Defines a contract that multiple classes must follow	Provides a base class with some common functionality

Interface

An interface in php is a contract, set of rules that classes need to follow. Interface define set of method that classes must impliment. Interface only contain signature/declaration of the methods. Classes that implement that interface implement those method according to the need.

When to use Interfaces

We use Interface when we want to define contract that multiple classes must follow without enforcing them to specific implementation.

Use Cases:

1. When multiple unrelated classes need to implement same method according to their requirement.
2. This provide consistency across multiple classes.
3. This also come in use when you want to implement dependency injection

 Abstract Class

Abstract class in php is a class that cannot be instantiated and it is meant to be extended by other classes. Abstract class have at least one abstract method. It provide its declaration but implemented by sub classes. Abstract class can have both abstract method(without implementation) and regular method(with implementation).

When to use abstract class

We use abstract class when we want partial implementation of functionality that multiple related classes should inherit.

Use Cases:

1) Creating base class with shared common logic. (The properties and method can be use in child classes)

2) Child classes needs to share properties or default behavior.

3) When you want to enforce child classes to implement specific method.

Final Thoughts

Use an interface when you want to define behavior but not enforce how it is implemented.