Java – what is the meaning of the three points in the function parameters?

There is already an answer to this question: > java, 3 dots in parameters8

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");
     }
 }

The question is, what are the three points of doinbackground (URL... URLs)?

Solution

This is not an Android feature This is a Java feature (added in Java 5), so you can use the "custom" parameter

This method:

protected Long doInBackground(URL... urls) {
  for (URL url : urls) {
    // Do something with url
  }
}

And this:

protected Long doInBackground(URL[] urls) {
  for (URL url : urls) {
    // Do something with url
  }
}

The internal method is the same The whole difference is the way you call For the first (also known as varargs), you can do this simply:

doInBackground(url1,url2,url3,url4);

But for the second, you have to create an array, so if you try to do this on one line, it's like:

doInBackground(new URL[] { url1,url3 });

Well, if you try to call a method written in varargs in this way, it will work in the same way as whether or not (backward support)