what does the three dots in "doInBackground(URL... urls)" mean?

Question

what does the "..." in each function mean? and why in the last function, there is no "..."?

private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
     protected Long doInBackground(URL... urls) {
         int count = urls.length;
         long totalSize = 0;
         for (int i = 0; i < count; i++) {
             totalSize += Downloader.downloadFile(urls[i]);
             publishProgress((int) ((i / (float) count) * 100));
             // Escape early if cancel() is called
             if (isCancelled()) break;
         }
         return totalSize;
     }

     protected void onProgressUpdate(Integer... progress) {
         setProgressPercent(progress[0]);
     }

     protected void onPostExecute(Long result) {
         showDialog("Downloaded " + result + " bytes");
     }
 }

Answer 1

Very short (and basic) answer: That represents a variable number of items "converted" to an array and it should be the last argument. Example:

test("string", false, 20, 75, 31);

void test(String string, boolean bool, int... integers) {
    // string = "string"
    // bool = false
    // integers[0] = 20
    // integers[1] = 75
    // integers[2] = 31
}

But you can also call

test("text", true, 15);

or

test("wow", true, 1, 2, 3, 4, 5, 6, 7, 8, 9, 100, 123, 345, 9123);