Web 9 | OOP in PHP

Mohammad Imam Hossain, Lecturer, dept. of CSE, UIU. Email: imambuet11@gmail.com
Object Oriented PHP
Basic class definitions begin with the keyword class, followed by a class name, followed by a pair of curly braces which
enclose the definitions of the properties and methods belonging to the class.
<?php
class SimpleClass
{
// property declaration
public $var = 'a default value';
// method declaration
public function displayVar() {
echo $this->var;
}
}
$instance = new SimpleClass();
$instance->var = '$assigned will have this value';
var_dump($instance);
?>
Constructor and Destructor:
<?php
class MyDestructableClass
{
function __construct() {
print "In constructorn";
}
function __destruct() {
print "Destroying " . __CLASS__ . "n";
}
}
$obj = new MyDestructableClass();
Visibility:
1. Property
<?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
?>
2. Method
<?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

Inheritance:
A class can inherit the methods and properties of another class by using the keyword extends in the class declaration. It
is not possible to extend multiple classes; a class can only inherit from one base class.
<?php
class Foo
{
public function printItem($string)
{
echo 'Foo: ' . $string . PHP_EOL;
}
public function printPHP()
{
echo 'PHP is great.' . PHP_EOL;
}
}
class Bar extends Foo
{
public function printItem($string)
{
echo 'Bar: ' . $string . PHP_EOL;
}
}
$foo = new Foo();
$bar = new Bar();
$foo->printItem('baz'); // Output: 'Foo: baz'
$foo->printPHP(); // Output: 'PHP is great'
$bar->printItem('baz'); // Output: 'Bar: baz'
$bar->printPHP(); // Output: 'PHP is great'
?>
Scope Resolution Operator:
<?php
class MyClass {
const CONST_VALUE = 'A constant value';
}
class OtherClass extends MyClass
{
public static $my_static = 'static var';
public static function doubleColon() {
echo parent::CONST_VALUE . "n";
echo self::$my_static . "n";
}
}

$classname = 'OtherClass';
OtherClass::doubleColon();
?>
Class Abstraction:
<?php
abstract class AbstractClass
{
// Force Extending class to define this method
abstract protected function getValue();
abstract protected function prefixValue($prefix);
// Common method
public function printOut() {
print $this->getValue() . "n";
}
}
class ConcreteClass1 extends AbstractClass
{
protected function getValue() {
return "ConcreteClass1";
}
public function prefixValue($prefix) {
return "{$prefix}ConcreteClass1";
}
}
class ConcreteClass2 extends AbstractClass
{
public function getValue() {
return "ConcreteClass2";
}
public function prefixValue($prefix) {
return "{$prefix}ConcreteClass2";
}
}
$class1 = new ConcreteClass1;
$class1->printOut();
echo $class1->prefixValue('FOO_') ."n";
$class2 = new ConcreteClass2;
$class2->printOut();
echo $class2->prefixValue('FOO_') ."n";
?>

Object Interfaces:
<?php
// Declare the interface 'iTemplate'
interface iTemplate
{
public function setVariable($name, $var);
public function getHtml($template);
}
// Implement the interface
// This will work
class Template implements iTemplate
{
private $vars = array();
public function setVariable($name, $var)
{
$this->vars[$name] = $var;
}
public function getHtml($template)
{
foreach($this->vars as $name => $value) {
$template = str_replace('{' . $name . '}', $value, $template);
}
return $template;
}
}
?>

Web 9 | OOP in PHP

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