未来和承诺之间有什么区别？ [英] What's the difference between a Future and a Promise?

问题描述

Future 和 Promise 之间的区别是什么？

它们都像占位符一样对于未来的结果，但主要区别在哪里？

What's the difference between Future and Promise?
They both act like a placeholder for future results, but where is the main difference?

推荐答案

根据此讨论， Promise 最终被称为 CompletableFuture 包含在Java 8中，以及其javadoc 解释：

According to this discussion, Promise has finally been called CompletableFuture for inclusion in Java 8, and its javadoc explains:

可以明确完成的未来（设置其值和状态），并可用作CompletionStage ，支持在完成时触发的依赖功能和动作。

A Future that may be explicitly completed (setting its value and status), and may be used as a CompletionStage, supporting dependent functions and actions that trigger upon its completion.

列表中也给出了一个例子：

An example is also given on the list:

f.then((s -> aStringFunction(s)).thenAsync(s -> ...);

请注意，最终的API略有不同，但允许类似的异步执行：

Note that the final API is slightly different but allows similar asynchronous execution:

CompletableFuture<String> f = ...;
f.thenApply(this::modifyString).thenAccept(System.out::println);

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