如何通过使用lambda在Groovy中创建java.concurrent.Callable对象？

Question

我发现我做不到

ExecutorService executorService = Executors.newSingleThreadExecutor()


Callable<String> stringCallable = {
    "hello world"
} as Callable<String>


Future<String> f = executorService.submit(stringCallable)

println f.get()
executorService.shutdown()

输出为：

null

但是当我直接跑步时：

println stringCallable.call()

输出为：

"hello world"