274 lines
6.5 KiB
Markdown
274 lines
6.5 KiB
Markdown
---
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title: Class Inheritance
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---
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## Class Inheritance
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_REUSE CODE WITH INHERITANCE IN OBJECT ORIENTED PROGRAMMING_
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Here, we will talk about how we can re-use code that we wrote without having any code duplication by using inheritance.
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### Man Class
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This is our `Man` class:
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```php
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<?php
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class Man
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{
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// 1. Declare the class variables
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public $name;
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protected $age;
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public $height;
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public $fav_sports;
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private $fav_drinks;
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// 2. Create a constructor method with 3 required parameters: name, age and height
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public function __construct($name, $age, $height)
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{
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// 2A. Assign the values of parameters to class properties
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// Also known as instance variables
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// Using "$this->property_name"
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$this->name = $name;
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$this->age = $age;
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$this->height = $height;
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// 2B. Print out the man's attributes and values upon instantiation
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echo "Our man's name is: " . $this->name . "\n";
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echo "He is " . $this->age . " years old and " . $this->height . " tall.";
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}
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// 3. Create class methods
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public function giveFirmHandshakes()
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{
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return "I give firm handshakes.";
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}
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public function beStubborn()
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{
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return "I am stubborn.";
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}
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public function notPutToiletPaper()
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{
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return "It's not humanly possible to remember to put toilet paper rolls when they are finished";
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}
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// 4. Age getter method
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public function getAge()
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{
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return $this->age;
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}
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// Age setter method
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public function setAge($age)
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{
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$this->age = $age;
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}
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// 5. Favorite Drinks setter method
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public function setFavDrinks($drinks = array())
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{
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if ($drinks) {
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$this->fav_drinks = $drinks;
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}
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}
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// Favorite Drinks getter method
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public function getFavDrinks()
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{
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return $this->fav_drinks;
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}
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}
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```
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### Healthy Man
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Let’s say we want to create another class called `HealthyMan` which has all the properties and methods of `Man` class.
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Without having to re-write all the code for `Man` class, we can re-use that code by using the keyword extends.
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```php
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<?php
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class HealthyMan extends Man
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{
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}
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```
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Now we have all the class properties and methods from Man inside `HealthyMan`. We can instantiate `HealthyMan` class to check this real quick.
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```php
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<?php
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$jackie = new HealthyMan('Jackie', 25, '5\' 5"');
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// => Our man's name is: Jackie
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// => He is 25 years old and 5' 5" tall.
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```
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We can go ahead and set HealthyMan aka Jackie’s favorite sports and drinks.
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```php
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<?php
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$jackie->fav_sports = ['swimming', 'weight training'];
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print_r($jackie->fav_sports);
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// =>
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// Array
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// (
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// [0] => swimming
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// [1] => weight training
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// )
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$jackie->setFavDrinks(['Matcha tea', 'Oolong Tea']);
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print_r($jackie->getFavDrinks());
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// =>
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// Array
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// (
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// [0] => Matcha tea
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// [1] => Oolong Tea
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// )
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```
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Now let’s see if we can call Man’s class methods like `giveFirmHandshakes()`, `beStubborn()` and `notPutToiletPaper()`.
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```php
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<?php
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echo "\n" . $jackie->giveFirmHandshakes();
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// => I give firm handshakes.
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echo "\n" . $jackie->beStubborn();
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// => I am stubborn.
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echo "\n" . $jackie->notPutToiletPaper();
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// => It's not humanly possible to remember to put toilet paper rolls when they are finished
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```
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We get all of these by just inheriting Man class using the keyword extends.
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### A Real Healthy Man
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If we just inherit `HealthyMan` from `Man` class and do nothing with it, then it beats the whole purpose.
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HealthyMan class has additional properties like `body_fat_percentage` and `workout_per_week`, and methods like `eatHealthy()`, `meditateDaily()` and `laughOften()`.
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Since these are personal properties, we can either set them visibility of protected or private and create setter/getter methods for the full encapsulation.
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```php
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<?php
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class HealthyMan extends Man
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{
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/**
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* HealthyMan properties
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*/
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private $body_fat_percentage;
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private $workout_per_week;
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/**
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* HealthyMan methods
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*/
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public function eatHealthy()
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{
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return "I only eat healthy meals.";
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}
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public function meditateDaily()
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{
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return "I set aside 20 minutes daily to meditate.";
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}
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public function laughOften()
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{
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return "I watch funny TV shows to unwind myself.";
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}
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/**
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* HealthyMan Setters and Getters
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*/
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public function setBodyFatPercentage($fat_percentage)
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{
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$this->body_fat_percentage = $fat_percentage;
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}
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public function getBodyFatPercentage()
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{
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return $this->body_fat_percentage;
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}
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public function setWorkoutPerWeek($workout_times)
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{
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$this->workout_per_week = $workout_times;
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}
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public function getWorkoutPerWeek()
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{
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return $this->workout_per_week;
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}
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}
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```
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We can call these methods to see if they are working as expected:
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```php
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<?php
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echo "\n" . $jackie->eatHealthy();
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// => I only eat healthy meals.
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echo "\n" . $jackie->meditateDaily();
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// => I set aside 20 minutes daily to meditate.
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echo "\n" . $jackie->laughOften();
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// => I watch funny TV shows to unwind myself.
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$jackie->setBodyFatPercentage(12);
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echo "\nBody Fat %: " . $jackie->getBodyFatPercentage();
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// => Body Fat %: 12
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$jackie->setWorkoutPerWeek(5);
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echo "\nWorkout Times Per Week: " . $jackie->getWorkoutPerWeek();
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// => Workout Times Per Week: 5
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```
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We have successfully re-used the existing code and implemented a child class.
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### Is He That Stubborn?
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Even though he inherited `beStubborn()` from Man class, since Jackie is a healthy man, he is only stubborn only once in a while. We can have Healthy Man’s `beStubborn()` method to say “I am stubborn once in a while” instead of just plain old “I am stubborn” by overriding the parent class’ method.
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```php
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<?php
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class HealthyMan extends Man
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{
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.....
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.....
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public function beStubborn()
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{
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return "I am stubborn once in a while.";
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}
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.....
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.....
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}
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```
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Now when we can Jackie’s `beStubborn()` method, we will see a different output than before:
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```php
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<?php
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echo "\n" . $jackie->beStubborn();
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// => I am stubborn once in a while.
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```
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This demonstrates how method overriding works in OOP.
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By using method overriding, we are basically re-declaring the parent class’ method inside the child class.
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This way, any instance of the parent’s class maintains its original method whereas any instance of the child class has the modified or overridden method.
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