what does the three dots in “doInBackground(URL… urls)” mean?

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");
}
}

As Morrison said, the 

...

 syntax
is for a variable length list of arguments (

urls

 holds
more than one

URL

).

This is typically used to allow users of the 

AsyncTask

 to
do things like (in your case) pass in more than one URL to be fetched in the background. If you only have one URL, you would use your

DownloadFilesTask

 like
this:

DownloadFilesTask worker = new DownloadFilesTask();
worker.execute(new URL("http://google.com"));

or with multiple URLs, do this:

worker.execute(new URL[]{ new URL("http://google.com"),
new URL("http://stackoverflow.com") });

The 

onProgressUpdate()

 is
used to let the background task communicate progress to the UI. Since the background task might involve multiple jobs (one for each URL parameter),
it may make sense to publish separate progress values (e.g. 0 to 100% complete) for each task. You don't have to. Your background task could certainly choose to calculate a total progress
value, and pass that single value to

onProgressUpdate()

.

The 

onPostExecute()

 method
is a little different. It processes a single result, from the set of operations that were done in 

doInBackground()

.
For example, if you download multiple URLs, then you might return a failure code if any of them failed. The input parameter to 

onPostExecute()

 will
be whatever value you return from 

doInBackground()

.
That's why, in this case, they are both 

Long

values.

If 

doInBackground()

 returns 

totalSize

,
then that value will be passed on 

onPostExecute()

,
where it can be used to inform the user what happened, or whatever other post-processing you like.

If you really need to communicate multiple results as a result of your background task, you can certainly change the 

Long

 generic
parameter to something other than a 

Long

 (e.g.
some kind of collection).

From Stackoverflow  http://stackoverflow.com/questions/12665769/what-does-the-three-dots-in-doinbackgroundurl-urls-mean