CSC/ECE 517 Fall 2012/ch1 1w34 vd

Re- implantation of methods in PHP 5

The object model in PHP5 was rewritten to include OO features such as final, abstract and visibility for classes and methods and improve the overall performance of the language. Re-implantation of methods in Php 5 can be achieved in the following manner:

Object Inheritance

This is an important OO feature that PHP uses in its object model. When a subclass extends from a parent class, it inherits all the public and protected methods from the parent class. The issues that affect how the inherited methods behave are:

Method Visibility

All methods that are defined as ‘public’ and ‘protected’ in the parent class are ‘visible’ in the subclass. Public and protected are access modifiers that define the visibility of methods between different classes. Methods defined as ‘private’ access are not visible in the subclass. Methods declared without any access keyword are ‘public’.
Example:

<?php

class GameClass
{


public function_construct(){ } //Declare a public constructor


public function GamePublic(){ } //Declare a public method
protected function GameProtected(){ } //Declare a protected method
private function GamePrivate(){ }  //Declare a private method

function Play()  //This is public
{

$this->GamePublic();
$this->GameProtected();
$this->GamePrivate();

} 
}
?>
$mygame = new GameClass;
$mygame->GamePublic(); // Works
$mygame->GameProtected(); // Fatal Error
$mygame->GamePrivate(); // Fatal Error
$mygame->Play(); // Public, Protected and Private work




class BoardGame extends GameClass

{
//This is public

function PlayDice()
{

$this->GamePublic();

$this->GameProtected();

$this->GamePrivate(); // Fatal Error

 }

}

$myboard = new BoardGame;
$myboard->GamePublic(); // Works

$myboard->PlayDice(); // Public and Protected work, not Private


Overriding If a subclass defines a new method with the same name and signature as that of the method from the parent class then an object of the subclass calling that method will execute the implementation of the method defined in the subclass. Example: change this example for overriding

<?php
class game
{
public function game-name($string)
 {
 echo 'Game: ' . $string . PHP_EOL;
 }
 
public function play()
 {
 echo 'I like this game.' . PHP_EOL;
 }
}

class chess-game extends game
{
 public function game-name($string)
 {
 echo 'Board Game: ' . $string . PHP_EOL;
 }
}

$gm = new game ();
$cg = new chess-game();
$game->game-name('cricket'); // Output: 'Game: cricket'
$gm->play();       // Output: 'I like this game' 
$cg->game-name('chess'); // Output: 'Board Game: chess'
$cg->play();       // Output: 'I like this game'
?>

Scope Resolution When a subclass extends a class, then the overridden and overloaded methods of the parent class can be called, using the scope resolution operator (::) inside the subclass.

<?php
class ParentClass
{
protected function parentFunc()
 {
 echo "ParentClass::parentFunc()\n";
 }
}

class ChildClass extends ParentClass
{
// Override parent's definition
public function parentFunc()
 {
 // Call the parent function
 parent::parentFunc();
 echo "ChildClass::parentFunc()\n";
 }
}

$class = new ChildClass();
$class->parentFunc();
?>
Output
ParentClass::parentFunc()
ChildClass::parentFunc()

Class Abstraction

Abstract methods in PHP 5 are methods inside abstract class that only provide signature for the method without any actual implementation to it. An abstract method has an abstract keyword at the beginning of the method declaration. A class containing even a single abstract method should be declared as abstract by adding the abstract keyword to its declaration. Any class inheriting from an abstract class should provide implementation to all of the abstract methods or declare it abstract. No class can inherit from more than one abstract class. The inheriting class, should have the same signature for the inherited abstract methods and the same or less restrictive visibility as defined for the methods in the abstract class.

<?php
abstract class ParentAbstractClass
{
 // Method without definition
 abstract protected function getName();
 abstract protected function setName($name);
 // Method with definition
 public function printName()
 {
  print $this->getName() . "\n";
 }
}
class ConcreteChild extends ParentAbstractClass
{
 //Method from abstract class implemeted
 protected function getName() 
 {
  return "ConcreteChild";
 }
 //Method from abstract class implemeted
 public function setName($name) 
 {
  return "ConcreteChild : {$name}";
 }
}
class ConcreteChild2 extends ParentAbstractClass
{
//Method from abstract class implemeted
 public function getname() 
 {
  return "ConcreteChild2";
 }
//Method from abstract class implemeted
 public function setName($name) 
 {
  return "ConcreteChild2 : {$name}";
 }
}

$class1 = new ConcreteChild;
$class1->printName();
echo $class1->setName('FOO') ."\n";
$class2 = new ConcreteChild2;
$class2->printName();
echo $class2->setName('FOO') ."\n";
?>
The above example will output:
ConcreteChild
ConcreteChild : FOO
ConcreteChild2
ConcreteChild2 : FOO

Object Interfaces

Interface in php is a mechanism that specifies methods that a class requires to implement, without having to provide any implementation to these methods inside the interface. An interface is declared like any other class, just that it is prefixed by the interface keyword and none of its methods have any content to them. A class providing implementation to the methods of an interface has the implements keyword followed by the class name for that class. Similarly, an interface can be inherited by another interface so that, a class implementing the interface that is lowest in the inheritance hierarchy gets to implement the methods from all the interfaces. Methods inside the interface being implemented by a class should have the same signature as that of the interface. Note: An interface cannot be instantiated.

<?php
interface food
{
//Interface method with no implementation
 public function eat();
}

interface fruit
{
//Interface method with no implementation
 public function fruitName();
}

interface Apple extends food, fruit
{
//Interface method with no implementation
 public function juice();
}

class GreenApple implements Apple
{
//Implementing methods from all the interfaces
public function eat()
 {
 echo “Food: eat()”;
 }
public function fruitName()
 {
 echo “Fruit: fruitName()”;
 }
public function juice()
 {
 echo “Apple: juice()”;
 }
}
?>

The class GreenApple will implement all the methods that it has inherited from all the interfaces in inheritance hierarchy.