Question

This question is an exact duplicate of:
What does <> (angle brackets) mean in Java?

I am reading about AsyncTask in Android. I have this example code:

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));
         }
         return totalSize;
     }

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

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

And it is supposed to be called with:

new DownloadFilesTask().execute(url1, url2, url3);

I can’t understand what <URL, Integer, Long> means. I have seen them in some other classes like String<> but I don’t know what is the purpose of them.

Answer 1

It defines the types of generics.

---

For example:

List<Integer> list;

You declare a variable of class List. But List is declared like this, if I’m right:

public interface List<T> extends Collection<T>

The T is a placeholder for a type that the user of this class can define. In my example, I chose to fill in the T with Integer. In this case it means I’ll have a List of Integers.