Android : Post Array to php with JSON

I want to send an Array to a php file. I can do it with a single string, so the connection etc. works. But i dont know how to do it with an array and how to get the array at the php file.

So this is my class:

String[] nonUserArray = new String[ohne.size()];
        for (int i = 0; i < ohne.size(); i++) {

            nonUserArray[i] = ohne.get(i).getnummer();
            System.out.println("Array "+nonUserArray[i]);
        }


            List<Name ValuePair> params = new ArrayList<NameValuePair>();
             // This is still wrong...
            params.add(new BasicNameValuePair("nummer[]", nonUserArray[]));

My php file still is:

<?php 
$response = array();
if (isset($_POST['nummer'])) {
    $nummer = $_POST['nummer'];    
    require_once __DIR__ . '/db_connect.php';

    $db = new DB_CONNECT();

    //Hier wird die ID ausgelesen
    $getIdAusMySQL = 0;
    $getIdAusMySQL = mysql_query("SELECT id FROM User WHERE nummer = '$nummer'"); 

   ...

I dont know how to receive the array and put it in a loop inside the php file.

´ By the way, can someone tell me a good oppertunity to find errors inside a php file. something like system.out.println() in java/android. Thanks