以下使用CompletableFuture有什么问题？

Question

我是CompletableFuture的新手， 这是一个我想尝试的简单的

 CompletableFuture.supplyAsync( ()-> {System.out.println("async");});

当我尝试编译时，它给出了错误

Error:(23, 26) java: no suitable method found for supplyAsync(()->{ Syst[...]"); })
    method java.util.concurrent.CompletableFuture.<U>supplyAsync(java.util.function.Supplier<U>) 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.<U>supplyAsync(java.util.function.Supplier<U>,java.util.concurrent.Executor) is not applicable
      (cannot infer type-variable(s) U
        (actual and formal argument lists differ in length))

我想知道上面的问题是什么？

Answer 1

就像在错误消息中所说：

  

缺少返回值

供应商必须返回一个值。尝试：

CompletableFuture.supplyAsync(()-> {System.out.println("async"); return null;});

或者像Flown指出的那样，使用runAsync：

CompletableFuture.runAsync(()-> System.out.println("async"));