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Valeri Tandilashvili's Personal Professional Blog
Results: 1024
call parent class constructor from child class CODE
We can call parent class constructor from child class using 
parent
keyword
parent::__construct($name);
Complete example:
class User {
    public $username;

    function __construct($name) {
        $this->username = $name;
    }
}
class Admin extends User{
    public $admin_level;
    
    function __construct($name, $admin_level) {
        parent::__construct($name);
        $this->admin_level = $admin_level;
    }
}
$admin1 = new Admin('Tom', 'Manager');

echo $admin1->username;
echo "\n";
echo $admin1->admin_level;
If there is no constructor in child class, then parent class constructor will be called (when appropriate parameters are passed)
checkbox & radio differences
We can check as many checkboxes as we want, but we can only check one radio as long as they have the same name.
Context of THIS keyword CODE 
this
inside 
fn()
function refers to the global 
window
object. That is why 
firstName
and 
lastName
attributes are not accessible using 
this
keyword
let john = {
  firstName: 'John',
  lastName: 'Doe',
  driveCar() {
    function fn () {
      console.log(this.firstName + ' ' + this.lastName + ' is driving a car');  // "undefined undefined is driving a car"
      console.log(this);
    }
    fn(); // fn.call(this);
    console.log(this.firstName + ' ' + this.lastName + ' is driving a car'); 
    console.log(this)
  }
}

john.driveCar();
In order to fix the issue, one of the ways is to use 
call
function and pass the object that we want 
this
to refer to inside the 
fn()
function
fn.call(this);
Inside 
driveCar()
function 
this
refers to the 
john
object because it is called through 
john
object
john.driveCar();
preg_match
Checks username value against the rule: must be at least 6 characters long and at most 12 characters long, only allowed alphanumeric symbols
if (!preg_match('/^[a-zA-Z0-9]{6,12}$/', $username)) {
    $this->addError('username', 'username must be 6-12 chars & alphanumeric');
}
class implements several interfaces CODE
One class implements several interfaces and takes responsibility to define all methods from both interfaces. Also defines several private methods additionally
interface int1 {
    // Force Extending class to define these methods
    function getArea();
} 

interface int2 {
    function getPerimeter();
} 

class Circle implements int1, int2 {
    static $PI = 3.1415926536;
    public $radius;
    
    public function __construct($radius) {
        $this->radius = $radius;
    }

    public function getPI() {
        return self::$PI;
    }
    
    public function getArea() {
        return pow($this->radius, 2) * self::$PI;
    }
    
    public function getDiameter() {
        return $this->radius * 2;
    }
    
    public function getPerimeter() {
        return $this->radius * 2 * self::$PI;
    }
}

$circle1 = new Circle(5);
echo "\nPI: " . $circle1->getPI();
echo "\nArea: " . $circle1->getArea();
echo "\nDiameter: " . $circle1->getDiameter();
echo "\nPerimeter: " . $circle1->getPerimeter();
interface example CODE
In this example class 
Circle
implements 
CircleAbstract
interface. Therefore it must define 
getArea()
and 
getPerimeter()
methods 
interface CircleAbstract {
    // Force Extending class to define these methods
    function getArea();
    function getPerimeter();
} 

class Circle implements CircleAbstract {
    static $PI = 3.1415926536;
    public $radius;
    
    public function __construct($radius) {
        $this->radius = $radius;
    }

    public function getPI() {
        return self::$PI;
    }
    
    public function getArea() {
        return pow($this->radius, 2) * self::$PI;
    }
    
    public function getDiameter() {
        return $this->radius * 2;
    }
    
    public function getPerimeter() {
        return $this->radius * 2 * self::$PI;
    }
}

$circle1 = new Circle(5);
echo "\nPI: " . $circle1->getPI();
echo "\nArea: " . $circle1->getArea();
echo "\nDiameter: " . $circle1->getDiameter();
echo "\nPerimeter: " . $circle1->getPerimeter();
Inheritance example CODE
The child class extends parent class means that it borrows properties and methods from its parent
class User {
    public function მარტივიჯამი($num1,$num2) {
        return $num1 + $num2;
    }
}
class Admin extends User{
    
}
$admin1 = new Admin('Tom');

echo $admin1->მარტივიჯამი(4,5);
access modifiers / visibility modifiers CODE 
public
- visible from anywhere 
private
- visible only for the owner class 
protected
- visible only for the owner and it's child classes 
class User {
    public $username;
    public $friends = ['Tom','David'];

    function __construct($name) {
        $this->username = $name;
        print $this->username . "'s object is created'\n";
    }

    private function მარტივიჯამი($num1,$num2) {
        return $num1 + $num2;
    }
}
class Admin extends User{
    function sumNumbers($num1,$num2) {
        return $this->მარტივიჯამი($num1,$num2);
    }
}
$admin1 = new Admin('Tom');

echo $admin1->sumNumbers(4,5);
__clone method and clone function 
clone
function clones the object and 
__clone
method is going to call when the object gets cloned 
class User {
    public $username;
    public $friends = ['Tom','David'];

    function __construct($name) {
        $this->username = $name;
        print $this->username . "'s object is created'\n";
    }

    function __clone() {
        print $this->username . "'s object is cloned'\n";
    }
}
$user1 = new User('Tom');
$user2 = clone $user1;
<main>
Note: There must not be more than one 
<main>
element in a document. The 
<main>
element must NOT be a descendant of an 
<article>
, 
<aside>
, 
<footer>
, 
<header>
, or 
<nav>
element.
Results: 1024