PHP5 Tutorial OOPS - PHP5 Class Access Specifiers - public, private and protected

Posted on November 14th, 2007 by admin

In the earlier tutorials we have witnessed keywords like public, private and protected. These are nothing but access specifiers. So, lets understand what access specifiers are.

Definition of Access Specifiers
Access specifiers specify the level of access that the outside world (i.e. other class objects, external functions and global level code) have on the class methods and class data members. Access specifiers can either be public, private or protected.

Why do we need Access specifiers
Access specifiers are used as a key component of Encapsulation and Data Hiding. By using either of the access specifiers mentioned above i.e. public, private or protected you can hide or show the internals of your class to the outside world.

Explanation of each access specifier

1. Private
2. Protected
3. Public

1. Private
A private access specifier is used to hide the data member or member function to the outside world. This means that only the class that defines such data member and member functions have access them. Look at the example below:

class Customer {
	private $name;
 
	public function setName($name) {
		$this->name = $name;
	}
 
	public function getName() {
		return $this->name;
	}
}
 
$c = new Customer();
$c->setName("Sunil Bhatia");
echo $c->name; //error, $name cannot be accessed from outside the class
               //$name can only be accessed from within the class
 
echo $c->getName(); //this works, as the methods of the class have access
                    //to the private data members or methods

In the above example, echo $c->name will give you an error as $name in class Customer has been declared private and hence only be accessed by its member functions internally. Therefore, the following line echo $c->getName() will display the name.

2. Public
A public access specifier provides the least protection to the internal data members and member functions. A public access specifier allows the outside world to access/modify the data members directly unlike the private access specifier. Look at the example below:

class Customer {
	public $name;
 
	public function setName($name) {
		$this->name = $name;
	}
 
	public function getName() {
		return $this->name;
	}
}
 
$c = new Customer();
$c->setName("Sunil Bhatia");
echo $c->name;		// this will work as it is public.
$c->name = "New Name" ; // this does not give an error.

In the above example, echo $c->name will work as it has been declared as public and hence can be accessed by class member functions and the rest of the script.

3. Protected
A protected access specifier is mainly used with inheritance. A data member or member function declared as protected will be accessed by its class and its base class but not from the outside world (i.e. rest of the script). We can also say that a protected data member is public for the class that declares it and it’s child class; but is private for the rest of the program (outside world). Look at the example below:

 
class Customer {
	protected $name;
 
	public function setName($name) {
		$this->name = $name;
	}
 
	public function getName() {
		return $this->name;
	}
}
 
class DiscountCustomer extends Customer {
 
	private $discount;
 
	public function setData($name, $discount) {
		$this->name = $name; //this is storing $name to the Customer
				     //class $name variable. This works
				     // as it is a protected variable
 
		$this->discount = $discount;				 
	}
}
 
$dc = new DiscountCustomer();
$dc->setData("Sunil Bhatia",10);
echo $dc->name; // this does not work as $name is protected and hence
		// only available in Customer and DiscountCustomer class

In the above example, echo $dc->name will not work work $name has been defined as a protected variable and hence it is only available in Customer and DiscountCustomer class.

You will learn more about inheritance later in this tutorial series. You should revisit this tutorial and read more on the protected section again when you understand inheritance better.

Important Note of Access Specifier in PHP5
In PHP5, access specifiers are public by default. This means that if you don’t specify an access specifier for a data member or method then the default ‘public’ is applicable.

Feel free to write comments if you need more examples or if you need to ask a question on PHP5 Class. You can also subscribe to my notification service to be informed as an when a new tutorial article goes online. Subscribe Below

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Filed under: PHP, PHP Tutorials, PHP5 OOPS Tutorials

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Matt, on November 15th, 2007 at 3:03 am Said:

great series of tutorials, i hope you keep them coming,
thank you very much.

Rajes Bhatia, on January 14th, 2008 at 5:27 pm Said:

This tutorial is helpful to me to understand the concept of access specifiers in php5 but please give some example of their use in web programming.

As I am fresher and new in web development. I am good in oops concepts and want to implement in web development.

Thanks

Regards,

Rajesh Bhatia

Rahul Kumar, on February 23rd, 2008 at 12:57 pm Said:

Dear sir,
your php 5 OOP tutorial is very helpfull for me.
Now I understand that what is access specifiers and how these access specifiers works.
1. Private
2. Protected
3. Public
Thanks
Regards,
Rahul

Rakesh Bhatt, on March 3rd, 2008 at 3:30 pm Said:

Awesome.. Excellent Series.

The examples and explanation provided in each section seems quite friendly. no one has explained me things clearly as you have done..

Thanks Buddy

Hetal Sagar, on May 8th, 2008 at 11:35 am Said:

Conscies preicious and towards goal.
little and powerful explation.

want more from u on each topic of php5.
thanks.
hetalsagar(at)rediffmail(dot)com

Ahmed Fahim, on May 11th, 2008 at 7:43 pm Said:

I just read your tutorials once and i understood the differences of the PHP OOP access specifiers. Its very good tutorials and well explained. Thank you so much… I look forward to see a small PHP OOP application if possible in the future… God bless you…

Krishna Prasad, on June 17th, 2008 at 11:01 pm Said:

This is simplest and the easiest tutorial i have come across which explains in a very basic and understanding language without making it complex. It was really helpful for me.

Gerard Vignes, on September 26th, 2008 at 6:56 am Said:

Thanks Sunil for using simple examples that illustrate the concept without introducing lots of superfluous details. Your style is needed on the PHP documentation, which sometimes uses bizarre examples that do more to confuse than clarify. I especially appreciate your using a simple inheritance example to illustrate the use of protected visibility on class members. Many other sites try to illustrate this concept without inheritance, which doesn’t make much sense.

Iam, on December 1st, 2008 at 11:32 am Said:

This is simplest and the easiest tutorial i have come across which explains in a very basic and understanding language without making it complex. It was really helpful for me

your php 5 OOP tutorial is very helpfull for me.
Now I understand that what is access specifiers and how these access specifiers works.
1. Private
2. Protected
3. Public

agus, on December 11th, 2008 at 12:03 pm Said:

sir, your series of PHP 5 OOPS is very very usefull for me, many big thanks

Regard
Agus

agus, on December 13th, 2008 at 4:12 am Said:

Sir, what the difenrence if we declere the acces specifiers or not? e.g just write:
$name
or
var $name
rather than
public $name

Thank You

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