Interfaces

Interfaces provide a way of implementing multiple inheritance (not directly available in PHP) through the use of the keywords interface and implements.

Potentially, one could inherit from a parent class, and then inherit from that class and so in a chain like fashion. However, this would likely mean a number of the parents, parents, parents, etc, members might be included that might not be required, and avoids needing a very long trail like this:

class Test implements InterfaceA, InterfaceB, InterfaceC, InterfaceD, InterfaceE......InterfaceZ {}

Interfaces:

100% abstract classes
Cannot be instantiated
Contain just the method names, not their definitions (i.e. the inner guts of their code)
Act like a contract to the class implementing the specified interface
All method names within an interface have public visibility
The implementing class must define the methods

The interface simply uses the keyword interface, which is then used by the class using the interface by way of the keyword implements:

<?php
	interface person {
		function setName($myName);
		function getName();
		function setAge($myAge);
		function getAge();
	}
	interface scientist{
		function measure();
		function writePaper();
	}
	class Geek implements person, scientist {
		public $name;
		public $age;
		public function setName($myName){
			$this->name = $myName;
		}
		public function getName(){
			return $this->name ;
		}
		public function setAge($myAge){
			$this->age = $myAge;
		}
		public function getAge(){
			return $this->age ;
		}
		public function measure(){
			echo "$this->name has just made a measurement!<br>";
		}
		public function writePaper(){
			echo "$this->name has written a paper!<br>";
		}
	}
	$steve = new Geek();
	$steve->setName("Stephen Hawking");
	$steve->setAge(71);
	echo "The guy who invented big bangs: ". $steve->getName() . " is now " . $steve->getAge() . " years old!<br>";
	$steve->measure();
	$steve->writePaper();
	echo "<pre>" . var_export($steve, TRUE) . "</pre>" ;
?>

<?php

interface person {

function setName($myName);

function getName();

function setAge($myAge);

function getAge();

}

interface scientist{

function measure();

function writePaper();

}

class Geek implements person, scientist {

public $name;

public $age;

public function setName($myName){

$this->name = $myName;

}

public function getName(){

return $this->name ;

}

public function setAge($myAge){

$this->age = $myAge;

}

public function getAge(){

return $this->age ;

}

public function measure(){

echo "$this->name has just made a measurement!<br>";

}

public function writePaper(){

echo "$this->name has written a paper!<br>";

}

$steve = new Geek();

$steve->setName("Stephen Hawking");

$steve->setAge(71);

echo "The guy who invented big bangs: ". $steve->getName() . " is now " . $steve->getAge() . " years old!<br>";

$steve->measure();

$steve->writePaper();

echo "<pre>" . var_export($steve, TRUE) . "</pre>" ;

Save & refresh browser:

The guy who invented big bangs: Stephen Hawking is now 71 years old!
Stephen Hawking has just made a measurement!
Stephen Hawking has written a paper!

Geek::__set_state(array(
'name' => 'Stephen Hawking',
'age' => 71,
))

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