PHP 的單例模式代碼

class User {
    static function getInstance()
    {
    if (self::$instance == NULL) { // If instance is not created yet, will create it.
        self::$instance = new User();
    }
    return self::$instance;
    }
    private function construct() 
    // Constructor method as private  so by mistake developer not crate
    // second object  of the User class with the use of new operator
    {
    }
    private function clone()
    // Clone method as private so by mistake developer not crate 
    //second object  of the User class with the use of clone.
    {
    }


function Log($str)
{ 
echo $str;
}
static private $instance = NULL;

}
User::getInstance()->Log("Welcome User");</pre>