java - java泛型中声明类型void的目的

Question

我正在经历vogella's tutorial我可以解决这个问题:

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

我不确定这个 void 意味着什么以及为什么要使用它？

Answer 1

让我们看一下 AsyncTask 的文档:

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只是一个类型参数，类似于您给出 Integer、Float 等的方式。