classes interaction methods php

June 28, 2022

Lets say we have class B which extends class A. When creating new instance of class B and providing value into it that value is used in constructor of class A. Please check sample below.
I’m little bit confused about such behavior. If method "display" do not pass value into class A it should not get there, or am i missing something?

class A {
    protected $changeableString = 'initial value';

    protected function __construct($providedText)
    {
    $this->changeableString = $providedText;        
    }

    public function printString(){
        echo $this->changeableString;
    }
}
class B extends A {
    public function display(){
        echo $this->changeableString;
    }
}

$test = new B('provided value');
$test->display();

>Solution :

First of all the topic you are talking about is called Inheritance in Object-Oriented Programming (OOP).

If class B has no a construct (__construct) then PHP will call the construct of class A.

And about display function, think of it as an addition to everything in class A but will not be available in class A
So class B is like class A but has one more function called display.