How to create static properties and methods

class Category {
  private $id, $name;
  private static $objectCount = 0; // declare a static property
  public function __construct($id, $name) {
    $this->id = $id;
    $this->name = $name;
    self::$objectCount++; // update the static property
  }
  
  // A public method that gets the static property
  public static function getObjectCount(){
    return self::$objectCount;
  }

  // The rest of the methods for the Category class
}

$guitars = new Category(1, 'Guitars');
$basses = new Category(2, 'Basses');
echo("<p> Object count: " . Category::getObjectCount() . "</p>); // 2 
$drums = new Category(3, 'Drums');
echo("<p> Object count: " . Category::getObjectCount() . "</p>); // 3

echo("<p> Object count: $objectCount</p>);

Description

• A static property or static method is a property or method that belongs to a class, not to objects created from the class. You use the static keyword to create these types of properties and methods, which are also referred to as class properties and class methods.
• Inside a class, you can access a static property or method by coding the self keyword followed by a double colon and the property or method name.
• Outside a class, you can access a static property or method that’s public by coding the class name followed by a double colon and the static property or method name.
• When you access a static property, you must include the dollar sign at the begin-ning of the property’s name.
• In a PHP application, the code space is separate for each user, which means that each user runs its own copy of the code. As a result, static properties and methods aren’t shared between multiple users.