intermediate 15 min read

Inheritance & Polymorphism

Extending classes, overriding methods, parent calls, final keyword, and LSP.

Inheritance

class Animal {
    public function __construct(
        protected string \$name
    ) { }
    public function speak(): string {
        return "\$this->name makes a sound";
    }
}

class Dog extends Animal {
    public function speak(): string {
        return "\$this->name barks";
    }
}

Parent Constructor

class Puppy extends Dog {
    public function __construct(string \$name, private int \$age) {
        parent::__construct(\$name);
    }
}

Final Keyword

final class cannot be extended. final method cannot be overridden.

Polymorphism

Objects of different classes can be used interchangeably if they share a parent class or interface.

Examples

<?php
class Shape {
    public function area(): float { return 0; }
}
class Circle extends Shape {
    public function __construct(private float $radius) {}
    public function area(): float { return pi() * $this->radius ** 2; }
}
class Square extends Shape {
    public function __construct(private float $side) {}
    public function area(): float { return $this->side ** 2; }
}
$shapes = [new Circle(5), new Square(4)];
foreach ($shapes as $s) echo get_class($s) . ': ' . $s->area() . "\n";

Table of Contents

Related Lessons

Inheritance & Polymorphism

Inheritance

Parent Constructor

Final Keyword

Polymorphism

Examples

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