Appropriate to make this class static? - php

Question

I've got a small input helper class.
I read a lot that static classes are not the best to use. But I still haven't grasp why I shouldn't use static classes. I'm not that advanced yet, so maybe I will figure it out later on.
The reason I made it static is that it's not an object that's unique every time it's being called in my script.
Is it a good thing that I made the class static?
class Input {
public static function exists($type = 'post') {
switch($type) {
case 'post':
return (!empty($_POST)) ? true : false;
break;
case 'get':
return (!empty($_GET)) ? true : false;
break;
default:
return false;
break;
}
}
public static function get($input, $source = 'post') {
if($source == 'post' && isset($_POST[$input])) {
return $_POST[$input];
} else if($source == 'get' && isset($_GET[$input])) {
return $_GET[$input];
}
return false;
}
}
EDIT: Updated code
class Input {
private $_get,
$_post;
public function __construct($get, $post) {
$this->_get = $get;
$this->_post = $post;
}
public function exists($type = 'POST') {
switch($type) {
case 'POST':
return (!empty($this->_post)) ? true : false;
break;
case 'GET':
return (!empty($this->_get)) ? true : false;
break;
default:
return false;
break;
}
}
public function get($input, $source = 'POST') {
if($source == 'POST' && isset($this->_post[$input])) {
return $this->_post[$input];
} elseif($source == 'GET' && isset($this->_get[$input])) {
return $this->_get[$input];
}
throw new Exception('Undefined index: ' . $input);
}
}

Answer 1

Just because you have only one of something doesn't mean it has to be static. Especially in regard to Unit tests, static classes are hard to deal with.
Your class Input is bound to $_GET and $_POST. This means you can not use it in Unit tests.
If instead your class looked like this:
$input = new Input($_GET, $_POST);
ie. you give it the global dependencies, now Input can be tested because you can mock the values of $_GET and $_POST.

Answer 2

If you don't want a static class, you could do something like this :
class Input {
private $array;
function __construct($array) {
$this->array = $array;
}
public function exists() {
return isset($this->array);
}
public function get($input) {
if($this->exists() && isset($this->array[$input])) {
return $this->array[$input];
}
return false;
}
}
$get = new Input($_GET);
$value = $get->get('key');
$post = new Input($_POST);
$value = $post->get('key');