Object and Classes - ranjanui/php GitHub Wiki

• Introduced in version 4, rewritten in php5
• Classes can be considered as a collection of methods, variables and constants. They often reflect a real-world thing, like a Car class or a Fruit class. You declare a class only once, but you can instantiate as many versions of it as can be contained in memory. An instance of a class is usually referred to as an object.

Defining and using class

• => is used with array indexing
• -> is similar to . operator in other language. eg: $this->name

<?php
class User{
    
}

$user = new User(); 
?>

class User
{
    public $name;
    public $age;
    
    public function Describe()
    {
        return $this->name . " is " . $this->age . " years old";
    }
}

$user = new User();
$user->name = "John Doe";
$user->age = 42;
echo $user->Describe();

Constructor and destructor

• special functions which are automatically called when an object is created and destroyed

<?php
class Animal
{
    public $name = "No-name animal";
    
    public function __construct($name)
    {
        $this->name = $name;
    }
}

$animal = new Animal("Bob the Dog");
echo $animal->name;
?>

<?php
class Animal
{
    public $name = "No-name animal";
    
    public function __construct($name)
    {
        echo "I'm alive!";    
        $this->name = $name;
    }
    
    public function __destruct()
    {
        echo "I'm dead now :(";
    }
}

$animal = new Animal("Bob");
echo "Name of the animal: " . $animal->name;
?>

Access modifier

• 3 modifier -> private, protected and public

Inheritannce

class Animal{
    public $name;
    public function Greet(){
        return "Hello, I'm some sort of animal and my name is " . $this->name;
    }
}
class Dog extends Animal{
    public function Greet(){
        return "Hello, I'm a dog and my name is " . $this->name;
    }
}
$animal = new Animal();
echo $animal->Greet();
$animal = new Dog();
$animal->name = "Bob";
echo $animal->Greet();

Abstract Class

• can't instantiated. Instead, you typically inherit a set of base functionality from them in a new class.

abstract class Animal{
    public $name;
    public $age;    
    public function Describe(){
        return $this->name . ", " . $this->age . " years old";    
    }
    abstract public function Greet();
}
class Dog extends Animal{
    public function Greet(){
        return "Woof!";    
    }
    
    public function Describe(){
        return parent::Describe() . ", and I'm a dog!";    
    }
}
$animal = new Dog();
$animal->name = "Bob";
$animal->age = 7;
echo $animal->Describe();
echo $animal->Greet();

Static classes

• Both variables and methods on a class can be declared as static(shared variables)
• Static method cannot access non-static variables and methods
• Accessing static members require the double-colon operator instead of the -> operator

<?php
class User{
    public $name;
    public $age;
    public static $minimumPasswordLength = 6;
    
    public function Describe(){
        return $this->name . " is " . $this->age . " years old";
    }
    
    public static function ValidatePassword($password){
        if(strlen($password) >= self::$minimumPasswordLength)
            return true;
        else
            return false;
    }
}

$password = "test";
if(User::ValidatePassword($password))
    echo "Password is valid!";
else
    echo "Password is NOT valid!";
?>

Class constant

• Value will never change

<?php
class User{
    const DefaultUsername = "John Doe";
    const MinimumPasswordLength = 6;
}

echo "The default username is " . User::DefaultUsername;
echo "The minimum password length is " . User::MinimumPasswordLength;
?>

final keyword

• final class can not be inherited
• final function can not be overridden

final class Animal{
    public $name;
}

class Animal{
    final public function Greet(){
        return "The final word!";    
    }
}