Extending classes in PHP - Step-by-Step Execution

Concept Flow - Extending classes

Define Parent Class

↓

Define Child Class extends Parent

↓

Create Child Object

↓

Child inherits Parent methods/props

↓

Call methods on Child

↓

If method overridden, Child's version runs

↓

Program Ends

This flow shows how a child class inherits from a parent class, can override methods, and how objects use these methods.

Execution Sample

PHP

<?php
class Animal {
  public function speak() {
    echo "Animal sound\n";
  }
}

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

$dog = new Dog();
$dog->speak();
?>

This code defines a parent class Animal and a child class Dog that overrides the speak method. It creates a Dog object and calls speak.

Execution Table

Step	Action	Class/Method	Output	Notes
1	Define class Animal	Animal		Parent class created with speak() method
2	Define class Dog extends Animal	Dog		Child class created, inherits Animal
3	Create object $dog = new Dog()	Dog::__construct		Dog object created
4	Call $dog->speak()	Dog::speak	Bark!	Dog's speak() overrides Animal's
5	Program ends			Execution complete

💡 Program ends after calling Dog's speak method which outputs 'Bark!'

Variable Tracker

Variable	Start	After Creation	Final
$dog	undefined	object of Dog	object of Dog

Key Moments - 2 Insights

Why does $dog->speak() print 'Bark!' and not 'Animal sound'?

Because Dog class overrides the speak() method from Animal. See execution_table step 4 where Dog::speak runs instead of Animal::speak.

Does Dog class have access to Animal's methods if not overridden?

Yes, Dog inherits all methods from Animal. If Dog does not override a method, calling it on Dog object uses Animal's version.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 4?

A Animal sound

B No output

C Bark!

D Error

💡 Hint

Check the Output column in execution_table row with Step 4

At which step is the Dog object created?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the Action column for object creation in execution_table

If Dog did not override speak(), what would $dog->speak() output?

A Bark!

B Animal sound

C No output

D Error

💡 Hint

Refer to key_moments about method inheritance and overriding

Concept Snapshot

Extending classes in PHP:
class Child extends Parent {
  // Child inherits Parent's methods and properties
  // Can override methods by redefining them
}
Create child object: $obj = new Child();
Calling methods uses Child's version if overridden, else Parent's.

Full Transcript

This example shows how PHP classes can extend other classes. The parent class Animal has a method speak() that prints 'Animal sound'. The child class Dog extends Animal and overrides speak() to print 'Bark!'. When we create a Dog object and call speak(), it runs Dog's version, printing 'Bark!'. This demonstrates inheritance and method overriding in PHP classes.