[OOP Fundamentals] Two Pillars of Object-Oriented Programming: Part 2 of 2

00-Message.php

<?php
class Message
{
  public function send()
  {
    echo "This message is sent from the Message class.\n";
  }

  public function receive()
  {
    echo "This message was received from the Message class.\n";
  }
}

01-SMSMessage.php

<?php
class SMSMessage extends Message
{
  public function send()
  {
    echo "This message is sent from the SMSMessage class.\n";
  }
}

02-FunctionalDemo1.php

<?php
$message = new Message();
$message->send();
$message->receive();

03-FunctionalDemo2.php

<?php
$message = new SMSMessage();
$message->send();
$message->receive();

04-WorkingDemo.php

<?php

class Message
{
  public function send()
  {
    echo "This message is sent from the Message class.\n";
  }

  public function receive()
  {
    echo "This message was received from the Message class.\n";
  }
}

class SMSMessage extends Message
{
  public function send()
  {
    echo "This message is sent from the SMSMessage class.\n";
  }
}

$message = new Message();
$message->send();
$message->receive();

$message = new SMSMessage();
$message->send();
$message->receive();