Description:
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This is the error I get when I run my script:

Fatal error: Access type for interface method Openable::open() must be omitted in C:\Program Files\Apache Group\Apache2\htdocs\zend\interface.Openable.php on line 3

These are my scripts:


interface.Openable.php
<?php
interface Openable {
	public abstract function open();
	public abstract function close();
}
?>

class.Jar.php
<?php
require_once('interface.Openable.php');

class Jar implements Openable {
	private $contents;
	
	public function __construct($contents) {
		$this->contents = $contents;
	}
	
	function open() {
		print "The jar is now open<br />";
	}
	
	function close() {
		print "The jar is now closed<br />";
	}
}
?>

testOpenable.php
<?php
	require_once('class.Jar.php');
	
	function openSomething(Openable $obj) {
		$obj->open();
	}
	
	$objJar = new Jar('Jelly');
	
	openSomething($objJar);
?>

If I remove the abstract keyword in interface.Openable.php I don't get the error. Is it because of PHP 5.1.2 and that I need to upgrade? 

Regards.