title: What's wrong on the following using CompletableFuture?
body: <p>I am new to CompletableFuture,
  here is a simple one I would like to try</p>
  
  <pre><code> CompletableFuture.supplyAsync( ()-&gt; {System.out.println("async");});
  </code></pre>
  
  <p>When I try to compile, it gave the error</p>
  
  <pre><code>Error:(23, 26) java: no suitable method found for supplyAsync(()-&gt;{ Syst[...]"); })
      method java.util.concurrent.CompletableFuture.&lt;U&gt;supplyAsync(java.util.function.Supplier&lt;U&gt;) is not applicable
        (cannot infer type-variable(s) U
          (argument mismatch; bad return type in lambda expression
            missing return value))
      method java.util.concurrent.CompletableFuture.&lt;U&gt;supplyAsync(java.util.function.Supplier&lt;U&gt;,java.util.concurrent.Executor) is not applicable
        (cannot infer type-variable(s) U
          (actual and formal argument lists differ in length))
  </code></pre>
  
  <p>I am wondering what's wrong with the above?</p>