PHP Abstract Classes

Intermediate~25 min read

Abstract classes are blueprints that can't be instantiated directly. They define methods that child classes MUST implement - perfect for enforcing structure!

<?php
// Abstract Classes

// Abstract class - cannot be instantiated
abstract class Shape
{
    protected $color;

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

// Abstract method - must be implemented by child classes
    abstract public function calculateArea();

// Concrete method - can be used by child classes
    public function getColor()
    {
        return $this->color;
    }
}

class Circle extends Shape
{
    private $radius;

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

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

class Rectangle extends Shape
{
    private $width;
    private $height;

public function __construct($color, $width, $height)
    {
        parent::__construct($color);
        $this->width = $width;
        $this->height = $height;
    }

public function calculateArea()
    {
        return $this->width * $this->height;
    }
}

$circle = new Circle("red", 5);
echo "Circle area: " . $circle->calculateArea() . "\n";

$rectangle = new Rectangle("blue", 10, 5);
echo "Rectangle area: " . $rectangle->calculateArea() . "\n";

Output

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Abstract Class

<?php
abstract class Shape {
    abstract public function calculateArea();
    
    public function describe() {
        echo "I am a shape";
    }
}

// $shape = new Shape();  // Error! Can't instantiate
?>

Implementing Abstract Methods

<?php
class Circle extends Shape {
    private $radius;
    
    public function calculateArea() {
        return pi() * $this->radius * $this->radius;
    }
}
?>

Summary

abstract class: Cannot be instantiated
abstract method: Must be implemented by child
Use case: Enforce structure across subclasses

What's Next?

Next, learn about Interfaces - contracts that classes must follow!

Previous Inheritance

Next Interfaces

Abstract Class

Implementing Abstract Methods

Summary

What's Next?

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