Development
030 December 2022

PHP Classes Explained

PHP classes are a way to define reusable code structures in PHP. They allow you to define the properties and behaviors of objects, and create multiple instances of those objects that share the same structure and behavior.

Here is a tutorial on how to use PHP classes:

  1. Defining a class: To define a class in PHP, use the class keyword followed by the name of the class. The class definition should be placed inside curly braces { }:
class MyClass {
  // class body
}

 

  1. Adding properties: To add properties to a class, use the var keyword followed by the property name. You can also specify the visibility of the property using the public, private, or protected keywords:
class MyClass {
  public $property1;
  private $property2;
  protected $property3;
}
  1. Adding methods: To add methods to a class, use the function keyword followed by the method name. You can also specify the visibility of the method using the public, private, or protected keywords:
class MyClass {
  public function method1() {
    // method body
  }
  private function method2() {
    // method body
  }
  protected function method3() {
    // method body
  }
}

In object-oriented programming (OOP), "public", "private", and "protected" are visibility keywords that determine the accessibility of class properties and methods.

  • Public methods and properties can be accessed from anywhere, inside or outside the class. They can be called and modified by any code.
  • Private methods and properties can only be accessed from within the class. They cannot be called or modified by code outside the class.
  • Protected methods and properties can only be accessed from within the class and its child classes. They cannot be called or modified by code outside the class hierarchy.

Here is an example of how these visibility keywords can be used in a PHP class:

class MyClass {
  public $property1 = 'public';
  private $property2 = 'private';
  protected $property3 = 'protected';

  public function method1() {
    echo $this->property1;
  }
  private function method2() {
    echo $this->property2;
  }
  protected function method3() {
    echo $this->property3;
  }
}

$object = new MyClass();

echo $object->property1; // prints 'public'
echo $object->property2; // produces an error
echo $object->property3; // produces an error

$object->method1(); // prints 'public'
$object->method2(); // produces an error
$object->method3(); // produces an error

In this example, the property1 and method1 members are public, the property2 and method2 members are private, and the property3 and method3 members are protected. The code outside the class can only access the public members, while the code inside the class can access all the members.

Visibility keywords are used to control the accessibility of class members and help to enforce encapsulation, which is a fundamental principle of OOP. By making some members private or protected, you can prevent other code from accidentally or intentionally modifying or accessing sensitive data or behavior. This can help to reduce the risk of bugs and improve the maintainability of your code.

  1. Creating an object: To create an object from a class, use the new operator followed by the class name:
$object = new MyClass();
  1. Accessing properties and methods: To access the properties and methods of an object, use the arrow operator ->:
$object->property1 = 'value';
$object->method1();
  1. Constructors and destructors: A class can have a special method called a constructor, which is automatically called when an object is created. Similarly, a class can have a special method called a destructor, which is automatically called when an object is destroyed. To define a constructor or destructor, use the __construct and __destruct methods:
class MyClass {
  function __construct() {
    // constructor body
  }
  function __destruct() {
    // destructor body
  }
}

 

  1. Inheritance: A class can inherit the properties and methods of another class by using the extends keyword. The child class can override or extend the inherited methods as needed:
class ParentClass {
  public function method1() {
    // method body
  }
}

class ChildClass extends ParentClass {
  public function method1() {
    // override method1
  }
  public function method2() {
    // new method
  }
}

This tutorial provides a basic overview of how to use PHP classes. There are many other concepts and features related to classes in PHP, such as interfaces, abstract classes, static methods and properties, and more. You can learn more about these topics and explore the full capabilities of PHP classes in the PHP documentation.

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