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>" ;
?>

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