Constructors and Destructors

Autoloading Classes
November 14, 2018
Visibility
November 14, 2018

Constructor

void __construct ([ mixed $args = “” [, $... ]] )

PHP 5 allows developers to declare constructor methods for classes. Classes which have a constructor method call this method on each newly-created object, so it is suitable for any initialization that the object may need before it is used.

NoteParent constructors are not called implicitly if the child class defines a constructor. In order to run a parent constructor, a call to parent::__construct() within the child constructor is required. If the child does not define a constructor then it may be inherited from the parent class just like a normal class method (if it was not declared as private).

Example #1 using new unified constructors

<?php
class BaseClass {
function __construct() {
print "In BaseClass constructor\n";
}
}
class SubClass extends BaseClass {
function __construct() {
parent::__construct();
print “In SubClass constructor\n”;
}
}class OtherSubClass extends BaseClass {
// inherits BaseClass’s constructor
}

// In BaseClass constructor
$obj = new BaseClass();

// In BaseClass constructor
// In SubClass constructor
$obj = new SubClass();

// In BaseClass constructor
$obj = new OtherSubClass();
?>

Destructor

void __destruct ( void )

PHP 5 introduces a destructor concept similar to that of other object-oriented languages, such as C++. The destructor method will be called as soon as there are no other references to a particular object, or in any order during the shutdown sequence.

Example #3 Destructor Example

<?php

class MyDestructableClass
{
function __construct() {
print “In constructor\n”;
}

function __destruct() {
print “Destroying ” . __CLASS__ . “\n”;
}
}

$obj = new MyDestructableClass();

Like constructors, parent destructors will not be called implicitly by the engine. In order to run a parent destructor, one would have to explicitly call parent::__destruct() in the destructor body. Also like constructors, a child class may inherit the parent’s destructor if it does not implement one itself.

The destructor will be called even if script execution is stopped using exit(). Calling exit() in a destructor will prevent the remaining shutdown routines from executing.

Visibility

The visibility of a property, a method or (as of PHP 7.1.0) a constant can be defined by prefixing the declaration with the keywords publicprotected or private. Class members declared public can be accessed everywhere. Members declared protected can be accessed only within the class itself and by inheriting and parent classes. Members declared as private may only be accessed by the class that defines the member.

Property Visibility

Class properties must be defined as public, private, or protected. If declared using var, the property will be defined as public.

Example #1 Property declaration

<?php
/**
* Define MyClass
*/
class MyClass
{
public $public = 'Public';
protected $protected = 'Protected';
private $private = 'Private';

function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}

$obj = new MyClass();
echo $obj->public; // Works
echo $obj->protected; // Fatal Error
echo $obj->private; // Fatal Error
$obj->printHello(); // Shows Public, Protected and Private

/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// We can redeclare the public and protected properties, but not private
public $public = 'Public2';
protected $protected = 'Protected2';

function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}

$obj2 = new MyClass2();
echo $obj2->public; // Works
echo $obj2->protected; // Fatal Error
echo $obj2->private; // Undefined
$obj2->printHello(); // Shows Public2, Protected2, Undefined

?>

Method Visibility

Class methods may be defined as public, private, or protected. Methods declared without any explicit visibility keyword are defined as public.

Example #2 Method Declaration

<?php
/**
* Define MyClass
*/
class MyClass
{
// Declare a public constructor
public function __construct() { }

// Declare a public method
public function MyPublic() { }

// Declare a protected method
protected function MyProtected() { }

// Declare a private method
private function MyPrivate() { }

// This is public
function Foo()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate();
}
}

$myclass = new MyClass;
$myclass->MyPublic(); // Works
$myclass->MyProtected(); // Fatal Error
$myclass->MyPrivate(); // Fatal Error
$myclass->Foo(); // Public, Protected and Private work

/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// This is public
function Foo2()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate(); // Fatal Error
}
}

$myclass2 = new MyClass2;
$myclass2->MyPublic(); // Works
$myclass2->Foo2(); // Public and Protected work, not Private

class Bar
{
public function test() {
$this->testPrivate();
$this->testPublic();
}

public function testPublic() {
echo "Bar::testPublic\n";
}

private function testPrivate() {
echo "Bar::testPrivate\n";
}
}

class Foo extends Bar
{
public function testPublic() {
echo "Foo::testPublic\n";
}

private function testPrivate() {
echo "Foo::testPrivate\n";
}
}

$myFoo = new Foo();
$myFoo->test(); // Bar::testPrivate
// Foo::testPublic
?>

Constant Visibility

As of PHP 7.1.0, class constants may be defined as public, private, or protected. Constants declared without any explicit visibility keyword are defined as public.

Example #3 Constant Declaration as of PHP 7.1.0

<?php
/**
* Define MyClass
*/
class MyClass
{
// Declare a public constant
public const MY_PUBLIC = 'public';

// Declare a protected constant
protected const MY_PROTECTED = 'protected';

// Declare a private constant
private const MY_PRIVATE = 'private';

public function foo()
{
echo self::MY_PUBLIC;
echo self::MY_PROTECTED;
echo self::MY_PRIVATE;
}
}

$myclass = new MyClass();
MyClass::MY_PUBLIC; // Works
MyClass::MY_PROTECTED; // Fatal Error
MyClass::MY_PRIVATE; // Fatal Error
$myclass->foo(); // Public, Protected and Private work

/**
* Define MyClass2
*/
class MyClass2 extends MyClass
{
// This is public
function foo2()
{
echo self::MY_PUBLIC;
echo self::MY_PROTECTED;
echo self::MY_PRIVATE; // Fatal Error
}
}

$myclass2 = new MyClass2;
echo MyClass2::MY_PUBLIC; // Works
$myclass2->foo2(); // Public and Protected work, not Private
?>

Visibility from other objects

Objects of the same type will have access to each others private and protected members even though they are not the same instances. This is because the implementation specific details are already known when inside those objects.

Example #4 Accessing private members of the same object type

<?php
class Test
{
private $foo;

public function __construct($foo)
{
$this->foo = $foo;
}

private function bar()
{
echo 'Accessed the private method.';
}

public function baz(Test $other)
{
// We can change the private property:
$other->foo = 'hello';
var_dump($other->foo);

// We can also call the private method:
$other->bar();
}
}

$test = new Test('test');

$test->baz(new Test('other'));
?>

The above example will output:

string(5) "hello"
Accessed the private method.
Sondiva Technologies
Sondiva Technologies
Sondiva Technologies started in 2011 with a vision of providing Quality based Web Hosting and Web Designing Services in Ghaziabad, Delhi NCR. Backed up by full stack developers and designers , with over 500+ Web Projects. They work on opensource Platforms like Wordpress, Magneto, Prestashop, Opencart and Core PHP. Other services are : Responsive Web Designing Domain Registration Services Dedicated & SSD Hosting Virtual Private Servers Google GSuite Mail Servers E-Commerce Shopping Portal Development Web Designing & Application Courses SEO & Digital Marketing

Leave a Reply

Your email address will not be published. Required fields are marked *

Shop Now