OOPS-Static keyword,Singleton Design Pattern and its implementation

Static keyword is useful in creating Singleton design pattern because in such a scenario changes made by 1 object to a variable is reflected in all the objects of that class in that request.

Here is my example code with Singleton Design Pattern.

What I was trying to do is I was trying a singleton object over different request's and was trying to see whether it maintains its state or not. And it doesn't I tried running this page from different browser's and I failed to retrieve data of previous request's or session's.

Singleton Pattern is just needed so that only one object access at a time a resource to avoid conflict's

Singleton's are used to write log's and database access,maintain configuration variable's.

And that is when I realized the importance of an Application Server over a Web Server where we can create application object's.

 <?php  
 session_start();  
 //Singleton class example  
 error_reporting(E_ALL);  
 final class UserInfo  
 {  
   static $user=null;  
   static $instance=NULL;  
   public static function Instance()  
   {  
     if (self::$instance === null) {  
       self::$instance = new UserInfo();  
     }  
     return self::$instance;  
   }  
   /*  
    * Shows the array  
    */  
   public static function showUser()  
   {  
     if(self::$user!=null)  
     {  
       foreach(self::$user as $key=>$value)  
       {  
         echo "<br/>Sessionid ".$key." is assigned to ".$value."<br/>";  
       }  
     }  
   }  
   /*  
    * Adds session Id and user to the array  
    */  
   public static function AddUser()  
   {  
     echo "<br/>";  
     echo "Object count is ==>";  
     echo $ucount=count(self::$user);  
     echo "<br/>";  
     if(self::$user===null)  
     {  
       self::$user=array();  
       self::$user[session_id()]="User ".($ucount+1);  
       //print_r(self::$user);  
     }  
     else   
     {  
       if(!(array_key_exists(session_id(),self::$user)))  
       {  
         self::$user[session_id()]="User ".$ucount+1;  
       }  
     }  
   }  
   private function __construct()  
   {  
   }  
 }  
 echo "My Session Id is :". session_id();  
 UserInfo::Instance()->AddUser();  
 $fact1= UserInfo::Instance();  
 $fact= UserInfo::Instance();  
 $fact1->AddUser();  
 $fact->showUser();  
 UserInfo::Instance()->showUser();  
 if($fact1===$fact)  
   echo "Matches";  
 /*  
  * ERROR LINE  
  */  
 //$fact3= new UserInfo();  
 ?>  

Output is:

 My Session Id is :p15snn5ebgn52ftsj0eb43e4n0  
 Object count is ==>0  
 Object count is ==>1  
 Sessionid p15snn5ebgn52ftsj0eb43e4n0 is assigned to User 1  
 Sessionid p15snn5ebgn52ftsj0eb43e4n0 is assigned to User 1  
 Matches  

As you can see above is mine singleton class with a private constructor.I have 2 static methods one to store data and other to show data

In first case I have added user name as value and corresponding session id as key to the array.
I have called my method in 2 way's directly via class and by an object.

In the second call count goes 1

Finally I call show user in 2 way's and the 2 object's matches as per the condition