12 OOP – III in PHP

Hiren Joshi

epgp books

 

 

 

Clone an object:

 

Working with objects, it may be required to copy an object. To make a copy of an object, the assignment operator (=) is used. The assignments operator just creates a new reference to the same object. In other words, both the variables points to the same object. So, if you change the properties of one object, that will also change the properties of other object too.

 

Let us check it by example.

 

<?php

class Employee

{

private $eid, $ename; // properties of a class Employee

public function __construct($eid,$ename)

{

$this->eid = $eid;

$this->ename = $ename;

}

 

// Getter and setter to set properties of object

 

public function geteid() //get method to get employeeid

{

return $this->eid;

}

public function seteid($value) //set method to set employeeid

{

$this->eid = $value;

}

      //getname

 

public function getename()

{

return $this->ename;

}

public function setename($value)

{

$this->ename = $value;

}

}

$obj1 = new Employee(101,’Vipul’);

echo ‘<br> $obj1 is now : ‘;

print_r($obj1);

$obj2 = new Employee(110,’Dhaval’);

echo ‘<br> $obj2 is now : ‘;

print_r($obj2);

$obj1 = $obj2;

echo ‘<br> after assignment operator now object 2 is <br>’; print_r($obj2);

echo ‘<br> after assignment operator now object 1 is <br>’; print_r($obj1);

echo “<br> set name of obj2 to vimal <br>”;

$obj2->setename(‘Vimal’);

echo ‘<br> $obj2 is after setname is: <br>  ‘;

print_r($obj2);

echo ‘<br> $obj1 is after obj2 setname is: <br> ‘;

print_r($obj1);

?>

 

Then the output will be:

 

$obj1 is now : Employee Object ( [eid:Employee:private] => 101 [ename:Employee:private] => Vipul )

$obj2 is now : Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

after assignment operator now object 2 is

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

after assignment operator now object 1 is

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

set name of obj2 to vimal

$obj2 is after setname is:

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Vimal )

$obj1 is after obj2 setname is:

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Vimal )

 

    To copy the object, clone keyword is also used.

The syntax to clone an object is:

clone <objectName>;

 

PHP makes a shallow copy of an object when an object is copied.

 

Shallow copy means it copies the memory location of an object. Changes in shallow copy is reflected on original object. To not create shallow copy, cloning of an object is required.

 

Let us understand the use of clone by example.

 

<?php

class Employee

{

private $eid, $ename; // properties of a class Employee

public function __construct($eid,$ename)

{

$this->eid = $eid;

$this->ename = $ename;

}

// Getter and setter to set properties of object

public function geteid()  //get method to get employeeid

{

return $this->eid;

}

public function seteid($value) //set method to set employeeid

{

$this->eid = $value;

}

 

//getname

   public function getename()

{

return $this->ename;

}

public function setename($value)

{

$this->ename = $value;

}

}

$obj1 = new Employee(101,’Vipul’);

echo ‘<br> $obj1 is now : ‘;

print_r($obj1);

$obj2 = new Employee(110,’Dhaval’);

echo ‘<br> $obj2 is now : ‘;

print_r($obj2);

$obj1 = clone $obj2;

echo ‘<br> after cloning now object 2 is <br>’;

print_r($obj2);

echo ‘<br> after cloning now object 1 is <br>’;

print_r($obj1);

echo “<br> set name of obj2 to vimal <br>”;

$obj2->setename(‘Vimal’);

echo ‘<br> $obj2 is after setname is: <br> ‘;

print_r($obj2);

echo ‘<br> $obj1 is after obj2 setname is: <br> ‘;

print_r($obj1);

$obj2->seteid(111);

echo ‘<br> $obj2 is after seteid is: <br> ‘;

print_r($obj2);

echo ‘<br> $obj1 is after obj2 seteid is: <br> ‘;

print_r($obj1);

?>

 

The output is:

 

$obj1 is now : Employee Object ( [eid:Employee:private] => 101 [ename:Employee:private] => Vipul )

$obj2 is now : Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

after cloning now object 2 is

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

after cloning now object 1 is

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

set name of obj2 to vimal

 

$obj2 is after setname is:

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Vimal )

$obj1 is after obj2 setname is:

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

$obj2 is after seteid is:

Employee Object ( [eid:Employee:private] => 111 [ename:Employee:private] => Vimal )

$obj1 is after obj2 seteid is:

Employee Object ( [eid:Employee:private] => 110 [ename:Employee:private] => Dhaval )

 

Inspecting an object

  • Inspecting an object is also known as introspection or reflection
  • There are many methods available for reflection. You can find out these methods through the URL http://www.php.net/manual/en/book.reflection.php
  • The following table summarize few of the very useful methods to inspecting an object.
  • These methods are used to check whether an object parameter is of expected type or not.
  • These methods are also used to make sure that a property or method exists before it is called.

 

Function Description
class_exists($class) Returns true if the $class is exists
get_class($object) Returns the class name of $object
is_a($object, $class) Returns true if $object is an instance of $class
property_exists($object, $property) Returns true if $property exists for $object
method_exists($object, $method) Returns true if $method exists for $object

 

 

Let us write a PHP code for above functions.

 

<?php

class Employee

{

private $eid, $ename; // properties of a class Employee

public function __construct($eid,$ename)

{

$this->eid = $eid;

$this->ename = $ename;

}

 

// Getter and setter to set properties of object

 

public function geteid() //get method to get employeeid

{

return $this->eid;

}

public function seteid($value) //set method to set employeeid

{

$this->eid = $value;

}

public function getename()

{

return $this->ename;

}

public function setename($value)

{

$this->ename = $value;

}}

$obj = new Employee(1,’Abhay’);

echo “<br> is class Employee exists: “;

//class_exists

$ans1 = class_exists(‘Employee’);

echo ” $ans1 “;

// get class

$ans2 = get_class($obj);

echo “<br> obj is object of class : $ans2”;

//is_a

$ans3 = is_a($obj,’Employee’);

if ($ans3 == true)

{

echo “<br> obj is an object of class Employee “;

}

else

{

echo “<br> obj is not an object of class Employee”;

}

 

//property_exists

 

$ans4 = property_exists($obj,’eid’);

if ($ans4 == true)

{

echo “<br> property eid exists for object obj “;

}

else

{

echo “<br> property eid does not exist for object obj “;

}

//method_exists

$ans5 = method_exists($obj,’geteid’);

if ($ans5 == true)

{

echo “<br> method geteid exists for object obj “;

}

else

{

echo “<br> method geteid does not exist for object obj “;

}

?>

 

The output of the above programmer is:

 

is class Employee exists: 1

obj is object of class : Employee

obj is an object of class Employee

property eid exists for object obj

method geteid exists for object obj

 

Inheritance

  • Inheritance is one of the essential concepts in Object Oriented Programing.
  • Inheritance allows developer to create a new class based on existing class.
  • The new class inherits all the properties and methods of class which is inherited.
  • The class which is inherited from the class is known as subclass or derived class or child class.
  • The class which is inherited by other class is known as superclass or base class or parent class.
  • The subclass can extend the inheritance by adding new properties and methods.
  • The subclass can override a method of the superclass. Method overriding means subclass use the same method name defined in super class.
  • A subclass can call a method of superclass. To call a super class method in subclass use the parent keyword then type :: (double colon) and then type the method name. The parent keyword refer to the super class.
  • Inheritance provide reusability of code.
  • Inheritance is used by the developers to develop consistent classes for large application.

 

The following code demonstrate an example of inheritance.

 

<?php

class Person

{

private $fname,$lname,$email,$mobile;

public function __construct($fname,$lname)

{

$this->fname = $fname;

$this->lname = $lname;

}

 

//fname

public function getfname()

{

return $this->fname;

}

public function setfname($value)

{

$this->fname = $value;

}

   //lname

 

public function getlname()

{

return $this->lname;

}

public function setlname($value)

{

$this->lname = $value;

}

//email

public function getemail()

{

return $this->email;

}

public function setemail($value)

{

$this->email = $value;

}

//mobile

public function getmobile()

{

return $this->mobile;

}

public function setmobile($value)

{

$this->mobile = $value;

}

}

class Employee extends Person

{

private $eid, $edept;

public function __construct($fname, $lname,$eid,$edept)

{

$this->eid = $eid;

$this->edept = $edept;

parent::__construct($fname,$lname);

}

 

//eid

 

public function geteid()

{

return $this->eid;

}

public function seteid($value)

{

$this->eid = $value;

}

 

//edept

 

public function getdept()

{

return $this->edept;

}

public function setedept($value)

{

$this->edept = $value;

}

}

$emp = new Employee(‘first’,’last’,1,’IT’);

print_r($emp);

$emp->setmobile(1234567890);

echo “<br>”;

print_r($emp);

?>

 

Then the output will be:

 

Employee Object ( [eid:Employee:private] => 1 [edept:Employee:private] => IT [fname:Person:private] => first [lname:Person:private] => last [email:Person:private] => [mobile:Person:private] => ) Employee Object ( [eid:Employee:private] => 1 [edept:Employee:private] => IT [fname:Person:private] => first [lname:Person:private] => last [email:Person:private] => [mobile:Person:private] => 1234567890 )

 

Access Modifier

 

The subclass inherits all the public and protected properties and methods while it cannot inherits private properties and methods.

 

Following table shows how the access modifier works

 

Modifier

 

 Access outside the

class?

 Access from

Subclass?
Public Yes Yes
Protected No Yes
Private No No

 

 

Following code show the use of protected access  modifier.

 

<?php

class Person

{

protected $fname,$lname;

private $email,$mobile;

public function __construct($fname,$lname)

{

$this->fname = $fname;

$this->lname = $lname;

}

 

//fname

 

public function getfname()

{

return $this->fname;

}

public function setfname($value)

{

$this->fname = $value;

}

 

//lname

 

public function getlname()

{

return $this->lname;

}

public function setlname($value)

{

$this->lname = $value;

}

//email

 

public function getemail()

{

return $this->email;

}

public function setemail($value)

{

$this->email = $value;

}

 

//mobile

 

public function getmobile()

{

return $this->mobile;

}

public function setmobile($value)

{

$this->mobile = $value;

}

}

 

class Employee extends Person

{

private $eid, $edept;

public function __construct($fname, $lname,$eid,$edept)

{

$this->eid = $eid;

$this->edept = $edept;

parent::__construct($fname,$lname);

}

 

//eid

 

public function geteid()

{

return $this->eid;

}

 

public function seteid($value)

{

$this->eid = $value;

}

 

//edept

 

public function getdept()

{

return $this->edept;

}

public function setedept($value)

{

$this->edept = $value;

}

//fullname

 

public function getfullname()

{

return $this->fname.’ ‘.$this->lname;

}

}

$emp = new Employee(‘first’,’last’,1,’IT’);

print_r($emp);

$emp->setmobile(1234567890);

echo “<br>”;

print_r($emp);

$full = $emp->getfullname();

echo “<h1> $full”;

?>

 

The output will be:

 

Employee Object ( [eid:Employee:private] => 1 [edept:Employee:private] => IT [fname:protected] => first [lname:protected] => last [email:Person:private] => [mobile:Person:private] => )

Employee Object ( [eid:Employee:private] => 1 [edept:Employee:private] => IT [fname:protected] => first [lname:protected] => last [email:Person:private] => [mobile:Person:private] => 1234567890 ) first last

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Reference:

 

1. Luke Welling, Laura Thomson: PHP and MySQL Web Development, Pearson,

2. W. Jason Gilmore: Beginning PHP and MySQL 5 From Novice to Professional,Apress

3. Elizabeth Naramore, Jason Gerner, Yann Le Scouarnec, Jeremy Stolz, Michael K.Glass: Beginning PHP5, Apache, and MySQL Web Development, Wrox,

4. Robin Nixon: Learning PHP, MySQL, and JavaScript, O’Reilly Media

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14. https://docs.oracle.com/javase/tutorial/java/concepts/

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