PHP Polymorphism Explained ( By Examples )

Introduction

Polymorphism is a fundamental concept in object-oriented programming (OOP) that allows objects of different classes to be treated as instances of a common superclass. In PHP, polymorphism enables you to write code that can work with objects of multiple types, providing flexibility and extensibility in your applications.

In PHP, polymorphism is achieved through method overriding and method overloading. Method overriding allows a child class to provide its own implementation of a method that is already defined in its parent class. This means that objects of different classes can respond differently to the same method call, based on their specific implementations. Method overloading, on the other hand, allows multiple methods with the same name but different parameter lists to coexist in a class. This enables you to perform different actions depending on the number or types of arguments passed to the method.

Polymorphism is particularly useful when working with class hierarchies and interfaces. It allows you to write code that operates on a superclass or interface, and it can seamlessly work with any derived class that adheres to that superclass or implements that interface. This promotes code reuse and simplifies the management of related classes, as you can treat them uniformly through their common superclass or interface.

One of the key benefits of polymorphism is the ability to write generic code that can accommodate future additions of new classes without requiring modifications to the existing code. This enhances the extensibility and maintainability of your PHP applications.

Polymorphism in PHP empowers you to write flexible and adaptable code by treating objects of different classes as instances of a common superclass or interface. It promotes code reuse, simplifies class management, and allows for the seamless integration of new classes into your application.

Example: How to Implement Polymorphism in PHP?

Here's an example of how to implement polymorphism in PHP using inheritance and interfaces:

Explanation
In this example, we have a parent class Animal with a common method makeSound(). The child classes Dog and Cat inherit from Animal and provide their own implementations of makeSound(). This demonstrates polymorphic behavior, as objects of Dog and Cat can be treated as instances of the parent class Animal.

Additionally, we have an interface CanFly that declares the fly() method. The Bird class implements this interface along with inheriting from Animal, allowing the Bird object to exhibit both polymorphic behavior (with makeSound() and interface-based behavior with fly()). By utilizing inheritance and interfaces, we achieve polymorphism in PHP, where different objects can share a common interface but have their own specific behaviors. Run the above code in your editor for a better and clear explanation.

Example no-2: Polymorphism with Interfaces

Explanation

In this example, the Shape interface as we can see declares the calculateArea() method. Then The Circle and Rectangle classes are used to implement the Shape interface and provide with their own implementations of the calculateArea() method. Although the implementations differ, objects of Circle and Rectangle can be treated as instances of the Shape interface, allowing polymorphic usage. Run the above code in your editor for a better and clear explanation.

Example 3: Polymorphism with Abstract Classes

Explanation

In this example, the Vehicle abstract class defines abstract methods start() and stop(). The Car and Bike classes extend the Vehicle class and provide their own implementations of these methods. Even though the implementations differ, objects of Car and Bike can be treated as instances of the abstract class Vehicle, demonstrating polymorphism. Run the above code in your editor for a better and clear explanation.

Types of PHP polymorphism

There are several types of polymorphism in PHP, each providing a different way to achieve flexible and dynamic behavior. Let's explore the most common types of polymorphism in PHP:

1. Compile-time Polymorphism (Method Overloading):

Compile-time polymorphism, also known as method overloading, allows the definition of multiple methods with the same name but different parameters in a class. The PHP interpreter determines which method to invoke based on the number and types of arguments passed during the function call.

In this example, the Math class has two add() methods with different numbers of parameters. The PHP interpreter determines the appropriate method to invoke based on the number of arguments provided. Run the above code in your editor for a better and clear explanation.

2. Runtime Polymorphism (Method Overriding):
Runtime polymorphism, also known as method overriding, occurs when a subclass provides its own implementation of a method that is already defined in its parent class. The overridden method in the subclass is called instead of the parent class method when an object of the subclass is used.

In this example, the Dog class extends the Animal class and overrides the makeSound() method. When makeSound() is called on a Dog object, it invokes the overridden method in the Dog class instead of the one in the Animal class. Run the above code in your editor for a better and clear explanation.

3. Polymorphism with Interfaces:

PHP interfaces provide a way to define a contract that classes must follow. Multiple classes can implement the same interface, enabling polymorphism by treating different objects as instances of the same interface. This allows objects of different classes to be used interchangeably when they implement the same methods defined by the interface.

In this example, the Shape interface declares the calculateArea() method. The Circle and Rectangle classes implement the Shape interface and provide their own implementations of calculateArea(). Despite having different implementations, objects of Circle and Rectangle can be treated as instances of the Shape interface, enabling polymorphism. Run the above code in your editor for a better and clear explanation.

4. Polymorphism with Abstract Classes:

Abstract classes in PHP provide a way to define common methods and properties that can be inherited by multiple subclasses. Abstract methods in abstract classes act as placeholders and must be implemented in the derived classes. Polymorphism can be achieved by creating objects of the derived classes and treating them as instances of the abstract class.

In this example, the Vehicle abstract class defines abstract methods start() and stop(). The Car and Bike classes extend the Vehicle class and provide their own implementations of these methods. Objects of Car and Bike can be treated as instances of the abstract class Vehicle, achieving polymorphism. Run the above code in your editor for a better and clear explanation.

These are some of the common types of polymorphism in PHP, each serving different purposes and enabling flexible and dynamic behavior in object-oriented programming. By leveraging these forms of polymorphism, developers can create more modular, extensible, and maintainable code.