PHP Classes For Beginners

jegan · #21 (**permalink**) 04-23-2008, 06:25 AM

eacy to use constructors in php class. when we creating a objects from using the new keyword the constructor function automatically executes

PHP Code:

  class Box

{

    var  width;

    var height;

 
        function box($pmWidth,$pmHeight)

{

    $this->width    =$pmWidth;

   $this->height=,$pmHeight;

}

function area()

{

    return $this->width*$this->height;

}

}

 
//This is syntax for Calling of constructor function 

$object        =    new Box(100,100);    //The new key word used to create an object

echo “Area of object box:”. $object->area();

output

Area of object box :1000

jegan · #22 (**permalink**) 04-23-2008, 06:27 AM

Using destructors

PHP Code:

  class Box

{

    var  width;

    var height;

    

        function ~box()

        {

           //Code for release the memory  

        }

}

 
Box1=new box ();    //it’s call the constructor function 

Delete box1;           //it’s call destructor function

saravanan · #23 (**permalink**) 04-24-2008, 06:14 AM

what is inheritance?

jegan · #24 (**permalink**) 04-24-2008, 06:17 AM

What is inheritance?

Probably the greatest feature of the PHP OOP model is Inheritance. Inheritance is the ability of PHP to extend classes (child classes) that inherit the characteristics of the parent class. The resulting object of an extend class has all the characteristics of the parent class, plus whatever is in the new child, or extended class. In this instance we will extend the vehicle class and add a motorcycle. A motorcycle is still a vehicle and shares many of the same attributes such as price, drive etc. But a motorcycle has some unique features that a car does not.

saravanan · #25 (**permalink**) 04-24-2008, 06:31 AM

give me simple example for inheritance?

jegan · #26 (**permalink**) 04-24-2008, 06:32 AM

Ans
I have written a program that inherits our Box class. Here the base class is Box and the derived class is BoxChild.
We have a scenario to find the weight of a box. So we need to write a new class with width, height and weigh member variables. But this will lead to us to do lot of workload. But we can inherit our Box object and we can add required thinks in child class.

PHP Code:

 
//Base class

<?php

class Box

{

    var  width;

    var height;

 
        function box($pmWidth,$pmHeight)

{

    $this->width    =$pmWidth;

   $this->height=,$pmHeight;

}

function area()

{

    return $this->width*$this->height;

}

}

//Child class

Class BoxChild extends Box

{

    var $weight

    function BoxChild($pmHeight,$pmWidth,$pmWeight)

    {

        $this->weigth=$pmWeight;

         parent::height=$pmHeight;

  parent::width=$pmWidth; 

}

function getWeight()

{

    return $this->weight;

}

}

?>

saravanan · #27 (**permalink**) 04-25-2008, 06:21 AM

what is access modifiers in php?

jegan · #28 (**permalink**) 04-25-2008, 06:24 AM

1. Restricting access to class properties (variable).
2. Restricting access to methods.
3. They support the concept of encapsulation, which promotes the idea of hiding functionality.
4. Access modifiers allow you to define who does or doesn’t have access to certain features in class

saravanan · #29 (**permalink**) 04-25-2008, 06:41 AM

what are the access modifiers available in php?

jegan · #30 (**permalink**) 04-25-2008, 06:43 AM

Access Modifiers
1. public
2. private
3. protected
4. Final

saravanan · #31 (**permalink**) 04-28-2008, 06:01 AM

how to use public access modifier in php?

jegan · #32 (**permalink**) 04-28-2008, 06:03 AM

Public variables and functions are accessible from anywhere in your script.

We can see in the below example that the public variable $num is set from user space and we call a public method that adds two the number and returns the value of $num+2. Having our properties (variables) visible or accessible from any part of our script works in our favors here, but it can also work against us. A could arise if we lost track of our values and changed the value of $num. To counter this problem we can create a method to set the value for us. Even with this in place it is still possible for somebody to simply access the $num variable. So we make the variable private. This ensures us that the property is only available within the class itself. It is private to the calling class.

PHP Code:

  
<?php

class mathematics
{
    /*** a number ***/
    public $num;
    public function addTwo()
       {
         Return $this->num+2;
    }
}
$math = new mathematics;

$math->num = 2;

echo $math->addTwo();

?>

saravanan · #33 (**permalink**) 04-28-2008, 06:05 AM

how to use protected access modifier in php?

jegan · #34 (**permalink**) 04-28-2008, 06:07 AM

Using Protected
Variables and functions marked as protected are accessible only through the object that owns them, whether or not they are declared in that object's class or whether they have descended from a parent class. Consider the following code:

PHP Code:

  <?php

    class dog {

        public $Name;

        private function getName() {

            return $this->Name;

        }

    }

 
    class poodle extends dog {

        public function bark() {

            print "'Woof', says " . $this->getName();

        }

    }

    

    $poppy = new poodle;

    $poppy->Name = "Poppy";

    $poppy->bark();

?>

In that code, the class poodle extends from class dog, class dog has a public variable $Name and a private function getName(), and class poodle has a public function called bark(). So, we create a poodle, give it a $Name value of "Poppy" (the $Name variable comes from the dog class), then ask it to bark(). The bark() function is public, which means we can call it as shown above, so this is all well and good.
However, note that the bark() function calls the getName() function, which is part of the dog class and was marked private - this will stop the script from working, because private variables and functions cannot be accessed from inherited classes. That is, we cannot access private dog functions and variables from inside the poodle class.
Now try changing bark() to protected, and all should become clear - the variable is still not available to the world as a whole, but handles inheritance as you would expect, which means that we can access getName() from inside poodle.

saravanan · #35 (**permalink**) 04-28-2008, 06:08 AM

how to use private access modifiers in php?

jegan · #36 (**permalink**) 04-28-2008, 06:09 AM

Private Variables
Private variable and method accessible only within the class. Not possible from outside of class.

PHP Code:

  <?php

    class dog 

{

        Private $Name;

        }

 
    class poodle extends dog

 { }

 
    $poppy = new poodle;

    $poppy->Name = "Poppy";

    print ($poppy);

 
?>

The derived class object try to access the private member variable of class dog. but it not possible to access from out side of class.

saravanan · #37 (**permalink**) 04-29-2008, 06:58 AM

what is inheritance ?

jegan · #38 (**permalink**) 04-29-2008, 07:01 AM

inheritance

Probably the greatest feature of the PHP OOP model is Inheritance. Inheritance is the ability of PHP to extend classes (child classes) that inherit the characteristics of the parent class. The resulting object of an extend class has all the characteristics of the parent class, plus whatever is in the new child, or extended class.

The most common is simplifying and reducing instances of redundant code that is code reusability.

jegan · #39 (**permalink**) 04-29-2008, 07:01 AM

what are types of inheritance in php?

jegan · #40 (**permalink**) 04-29-2008, 07:03 AM

Type of Inheritance

1.Single inheritance

2.Multi-level inheritance

3.Multiple inheritance can’t achieve in php.

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