🧰 PHP Abstract Classes – Complete Guide (2025 Edition)

Learn how to use abstract classes in PHP to create flexible and scalable object-oriented applications.

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🚀 Introduction – What Is an Abstract Class in PHP?

An abstract class in PHP is a class that cannot be instantiated directly. It serves as a blueprint for other classes. Abstract classes define common behavior and structure, and they often include abstract methods that must be implemented in child classes.

✅ Use abstract classes when you want to enforce a set of methods across multiple related classes, while sharing some common functionality.

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📌 Syntax of Abstract Classes in PHP

abstract class Animal {
    abstract public function makeSound();

    public function eat() {
        echo "Eating...\n";
    }
}

class Dog extends Animal {
    public function makeSound() {
        echo "Bark\n";
    }
}

🔹 abstract keyword is used to define both abstract classes and methods.
🔹 The makeSound() method must be implemented by any class that extends Animal.

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🧠 Key Features of Abstract Classes

Feature	Description
Cannot be instantiated	You cannot create objects directly from abstract classes.
May contain abstract methods	Methods without implementation (must be defined by subclass).
May contain concrete methods	Abstract classes can have regular methods with code.
Enforced implementation	All abstract methods must be implemented in the child class.
Support properties and constants	Abstract classes can define properties and constants like normal classes.

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🔍 Example – Abstract Class with Multiple Methods

abstract class Shape {
    protected $color;

    public function __construct($color = "red") {
        $this->color = $color;
    }

    abstract public function area();

    public function getColor() {
        return $this->color;
    }
}

class Circle extends Shape {
    private $radius;

    public function __construct($radius, $color = "red") {
        parent::__construct($color);
        $this->radius = $radius;
    }

    public function area() {
        return pi() * $this->radius * $this->radius;
    }
}

$circle = new Circle(5);
echo "Area: " . $circle->area();      // Output: Area: 78.5398...
echo "\nColor: " . $circle->getColor(); // Output: Color: red

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📦 When to Use Abstract Classes in PHP

Use Case	Why Use Abstract Classes?
Shared base class with common logic	Implement common methods once and abstract what varies.
Enforce method implementation	Require all subclasses to define certain behaviors (e.g., connect()).
Template pattern design	Provide a template for algorithms with overridable steps.

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🆚 Abstract Class vs Interface

Feature	Abstract Class	Interface
Method Body	Can have both abstract and concrete methods	Cannot have concrete methods (until PHP 8+)
Properties	Can have properties	Cannot have properties (until PHP 8.1+)
Multiple Inheritance	❌ No multiple abstract class inheritance	✅ Multiple interface implementation
Use Case	“is-a” relationships, shared base logic	Capability-based design (“can-do”)

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🧾 Summary

• PHP abstract classes help you build a strong OOP foundation by enforcing structure and contracts in derived classes.
• They allow code reuse through concrete methods and flexibility through abstract methods.
• Perfect for inheritance-based designs such as modeling real-world entities and behaviors.

🔧 Tip: Use abstract classes when multiple classes share common code, but need to define their own specific behaviors.

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❓ Frequently Asked Questions (FAQ)

🔹 Q1. Can I create an object from an abstract class?

A: No. Abstract classes cannot be instantiated directly. You must extend them in a concrete class.

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🔹 Q2. Can an abstract class have a constructor in PHP?

A: Yes. Abstract classes can have constructors which can be called from the child class using parent::__construct().

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🔹 Q3. Can abstract classes have properties?

A: Yes. Abstract classes can define and use properties just like regular classes.

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🔹 Q4. What happens if I don’t implement all abstract methods?

A: The child class will also need to be declared abstract, or PHP will throw a fatal error.

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🔹 Q5. Can an abstract class extend another abstract class?

A: Yes. You can create abstract class hierarchies, and each subclass can extend and implement the required methods progressively.

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