PHP-Loop Queston's

1. for($i=1;$i++;$i<100)
echo $i;

2. for($i=0;$i++;$i<100)
echo $i;

How many times will the loop execute in both the cases.

Answers:

1. Infinite why?
We know that for loop has 3 blocks 1st is assignment 2nd is condition and 3rd is increment.

Now in first block we have assignment $i=1 We are fine with it
In second block we are having $i++ which means that it will check for value of $i as condition before incrementing so $i=1 and increment $i to 2 and again in next pass we have $i=2 which is again true value>0 results in true.
and it will go on until falls short of memory.

2. 0 Why?

$i=0 initially checked that condition before increment $i=0 which returns false and as such loop halts.

OOPS-PHP-Magic Methods

1. __get($property)

Get value for a property set in a class foe example

 function __get($property)  
 {  
 return $this->properties[$property];  
 }  

Usage: echo $st->name;

2. __set($property,$value) Set value for a property

 function __set($property, $value)  
 {  
 $this->properties[$property]="AutoSet {$property} as: ".$value;  
 }  

Usage: $st->roll=16;

3. __call()
overloads any undefined function in a class.Thus we can also call an undefined function and show custom error message.

 function __call($method, $arguments)  
 {  
 echo "You called a method named {$method} with the following  
 arguments <br/>";  
 print_r($arguments);  
 echo "<br/>";  
 }  

Usage: $ol->notAnyMethod("boo");

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

OOPS-What is the difference between Static and Final Keyword

Static
A static method remains common for all objects and can be called directly without the need of creation of any object.

For Example : classname::functionname();

A static property on the other end remains common for all the objects.It preserves its last changed state by any object.

Final
Final keyword on other end does not allows a class to be extended a method to be overridden in subclass or to change a property respective to its use in a class.

OOPS-PHP4,PHP5-difference

1. In PHP4 there are no access modifiers everything is open we can't use public,private or protected for our methods.

2. In PHP4 there are interfaces but no abstract or final keyword.

An interface can be implemented by any object and which means that all the functions of interface must be implemented by the object.We can only declare the name and access type of any method in an interface.

An abstract class is where some methods may have some body too.

A final class cannot be extended.

3. In PHP4 there is no multiple inheritances for interfaces but Php5 supports multiple inheritance via implementing multiple interfaces together.

4. In PHP4 everything is static i.e if we declare any method in class which uses $this keyword we can call the same via classname::method() i.e. without instantiating the class which is not allowed in PHP5.

5. There is no class based constant,static property,destructor in PHP 4.

6. PHP 4 allows shallow copy of object.But in PHP 5 shallow copy is possible only via clone keyword.

7. PHP 4 does not have an exception object where as PHP 5 has an exception object.

8. Method over loading via magic functions like __get() and __set() is possible in PHP 5

OOPS-PHP-usefull functions

1. get_declared_classes();
Returns an array with the name of the defined classes.Useful when you have integrated a component or helper or vender class and what to know whether it's been included or not.

Differences between abstract class and interface in PHP

Following are some main difference between abstract classes and interface in php

1. In abstract classes this is not necessary that every method should be abstract. But in interface every method is abstract.
2. Multiple and multilevel both type of inheritance is possible in interface. But single and multilevel inheritance is possible in abstract classes.
3. Method of php interface must be public only. Method in abstract class in php could be public or protected both.
4. In abstract class you can define as well as declare methods. But in interface you can only defined your methods.