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Editorial Team
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Asked: 2026-05-22T23:55:25+00:00

The Android documentation has an example for using AsyncTask, in this example the DownloadFilesTask

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The Android documentation has an example for using AsyncTask, in this example the DownloadFilesTask class extends AsyncTask in a rather odd way (for a beginners perspective at least):

private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {

Shouldn’t AsyncTask be accepting type variables instead of primitive types? And what happens if I want to input strings in all 3 parameters? Like so:

private class DownloadFilesTask extends AsyncTask<String, String, String> {

How does the class then reference these parameters individually?

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1 Answer

  1. Editorial Team

    Those generic typs only define what kind of input types you have for <Param, Progress, Result> meaning that all the params to execute() are of type Param, those for onProgressUpdate are of Progress and that doInBackground() will return something of type Result. The generics only define the type of stuff that is expected later.

    If you have a decent IDE, when you define the class X extends AsyncTask<...> it will provide you with the callbacks where all the right types are filled in.

    In your 2nd example — that does not mean that execute() expects 3 Strings – actually it expects one or more variables of type Param, as it is a varargs signature. Within the method, you would then reference the individiual instances like accessing an array.

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