<?php
// sample code to illustrate the use of singleton design pattern
// http://royads.blogspot.com

class mysqlClass
{
 protected static $_instance;
 
 public $username;
 
 function __construct()
 {
 }
  
 public static function getInstance()
 {
   if(null === self::$_instance)
    {
      self::$_instance = new mysqlClass();
    }
    return self::$_instance;
 }
}
$singleDbConnection = mysqlClass::getInstance();
$singleDbConnection->username = 'user1';


$isItOtherDbConnection = mysqlClass::getInstance();
print $isItOtherDbConnection->username;
// c the output of above line it prints the value which is set by the first object. Now this is what is singleton.

?>