CODEWITHSUNDEEP
javaandroid
user3134565
user3134565

Reputation: 965

Purpose of type void declared in java generics

I was going through vogella's tutorial and i can across this:

private class DownloadWebPageTask extends AsyncTask<String, Void, String> {

I am not sure what this void means and why is it being used ?

Upvotes: 0

Views: 49

Answers (4)

Pierre Rust
Pierre Rust

Reputation: 2504

See AsyncTask javadoc :

Not all types are always used by an asynchronous task. To mark a type as unused, simply use the type Void:

private class MyTask extends AsyncTask<Void, Void, Void> { ... }

Void in generics simply means that your parameterised class will use void wherever this generic is used (generally for return value).

Upvotes: 0

bgplaya
bgplaya

Reputation: 1155

Void used there means that you are not going to publish results before async task finish.

Upvotes: 1

Rohit Jain
Rohit Jain

Reputation: 213411

Let's go through the documentation of AsyncTask:

The three types used by an asynchronous task are the following:

  • Params, the type of the parameters sent to the task upon execution.
  • Progress, the type of the progress units published during the background computation.
  • Result, the type of the result of the background computation.

Not all types are always used by an asynchronous task. To mark a type as unused, simply use the type Void:

private class MyTask extends AsyncTask<Void, Void, Void> { ... }

Void is just a type argument, similar to how you give Integer, Float, etc.

Upvotes: 2

Alexander
Alexander

Reputation: 48272

The second parameter goes into onProgressUpdate(). In case you do not want to make progress update notifications you pass Void as the second parameter and do not implement onProgressUpdate()

Upvotes: 1

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