从lambda表达式中的方法返回值 [英] Returning a value from a method within a lambda expression

问题描述

我正在试图弄清楚如何从lambda表达式返回一个方法值：

I'm trying to figure out how to return a method value from a lambda expression:

public int findMissingNumber(Collection<Integer> ints) {
    Single<Integer> start = new Single<>(1);
    ints.stream().mapToInt(Integer::valueOf).parallel().forEach(i -> {
        if (i != start.setValue(start.getValue() + 1)) {
            //return here
        }
    });
    return -1;
}

但是，似乎使用返回关键字将显式返回lambda函数本身。有没有某种方法可以打破或强制整个方法返回？

However, it seems that using the return keyword in the lambda expression will explicitly return to the lambda function itself. Is there some type of way to break or force a return for the entire method?

推荐答案

是有什么类型的方法来打破或强制整个方法的回报？

Is there some type of way to break or force a return for the entire method?

没有。至少，除非你抛出异常。

No. At least, not unless you throw an exception.

基本上，这不是 forEach 的意思。您可以编写一个接受函数的方法，该函数将返回 null 表示保持运行而非空表示停止，并使其成为结果......但是方法不是 forEach 。

Basically, that's not what forEach is meant for. You could write a method which accepted a function which would return null for "keep going" and non-null for "stop, and make this the result"... but that method isn't forEach.

你正在使用lambda的事实表达在这里是偶然的。想象一下，你只是在调用 forEach 并传入一些参数 - 如果那个调用你的那么它不会真的很奇怪findMissingNumber 方法返回（没有异常），没有 findMissingNumber 方法本身有return语句？

The fact that you're using a lambda expression is really incidental here. Imagine you were just calling forEach and passing in some argument - wouldn't it be really weird if that call made your findMissingNumber method return (without an exception), without the findMissingNumber method itself having the return statement?

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