Singleton pattern in php

Question

class SingleTon
{
    private static $instance;

    private function __construct()
    {
    }

    public function getInstance() {
        if($instance === null) {         


        

Answer 1

Yes, you have to call using

SingleTon::getInstance();

The first time it will test the private var $instance which is null and so the script will run $instance = new SingleTon();.

For a database class it's the same thing. This is an extract of a class which I use in Zend Framework:

class Application_Model_Database
{
   /**
    *
    * @var Zend_Db_Adapter_Abstract
    */
   private static $Db = NULL;

   /**
    *
    * @return Zend_Db_Adapter_Abstract
    */
   public static function getDb()
   {
      if (self::$Db === NULL)
         self::$Db = Zend_Db_Table::getDefaultAdapter();
      return self::$Db;
   }
}

Note: The pattern is Singleton, not SingleTon.