title: what is Future<void>?
body: <p>I have following code snippet.
  <br></p>
  
  <pre><code>import io.vertx.core.Future;
  public void start(Future&lt;void&gt; fut){
  
    /*
    some code
    */
    fut.complete()
  }
  </code></pre>
  
  <p><br>
  Why does <strong>Future</strong> used here?</p>