Abstract Class vs Interface

Understanding Abstract Classes and Interfaces in Magento 2

In Magento 2 development, Abstract Classes and Interfaces are key OOP concepts that help maintain clean, modular, and upgrade‑safe architecture. They define how classes interact and ensure consistency across modules.

Abstract Class

• An abstract class contains at least one abstract method — a method declared without a body.
• It can also include regular methods with implementations.
• We declare a class as abstract only when it has one or more abstract methods.

An abstract class acts as a partially implemented blueprint. It defines structure and behavior that child classes must complete. Developers use it when multiple classes share common logic but differ in specific implementations.

Key Notes on Abstract Classes

• Objects cannot be created directly from abstract classes.
• Child classes extending an abstract class must implement all abstract methods.
• If an abstract method is protected in the parent, its implementation must be protected or public — not private.
• Method signatures must match exactly; optional parameters are not allowed.

Abstract classes that declare all methods as abstract are not the same as interfaces. A class can implement multiple interfaces but can extend only one abstract class.

Interface

An Interface defines a contract that classes must follow. It contains only method declarations — no implementations. In Magento, interfaces are widely used for service contracts, ensuring consistent behavior across modules.

Rules for Interfaces

• All methods in an interface must be public.
• Classes implementing an interface must define all its methods.
• Method signatures must match exactly.
• Interfaces can extend other interfaces using the extends keyword.

Notes on Interfaces

• Objects cannot be created directly from an interface, but classes implementing it can.
• Interfaces cannot contain variables or properties.
• When an interface extends another, all methods must be implemented in the child class.

Abstract Class vs Interface

Abstract Class	Interface
Can have constants, properties, and both abstract and concrete methods.	Can only have constants and method declarations.
Methods can be public or protected.	All methods must be public.
Does not support multiple inheritance.	A class can implement multiple interfaces.
Child classes must implement all abstract methods.	Interfaces can extend other interfaces without requiring implementations.

Magento Example

In Magento 2, AbstractModel provides base functionality for entities like Product or Category, while ProductRepositoryInterface defines a contract for product operations. This combination of abstraction and interface ensures flexibility and consistency across modules.