Java中是否有最简单的reduce/fold方法? [英] Is there simplest possible reduce/fold method in java?

问题描述

我知道的其他技术(.Net，JS)包含最简单的折叠/减少操作:

Other technologies I know (.Net, JS) contain the simplest fold/reduce operation:

TResult reduce(TResult result, (TResult prevResult, TValue value) -> TResult)

我发现一种方法要求TValue和TResult为同一类型. 另一个要求提供结合2个TResults的BinaryOperation. 这些约束都不符合我的情况. 现在，我最终得到如下代码:

One method I found requires TValue and TResult to be the same type. Other one requires providing BinaryOperation that combines 2 TResults. None of those constraints matches my context. For now I ended up with code like:

Accumulator acc = someInitialValue;
for(Element element: list) {
    accumulator = reducer(accumulator, element);
}

但是我相信基本方法应该包含在流API中.

but I believe so the basic method should be contained in stream API.

我也看过收藏家，但没有发现任何帮助.

I have also taken a look for collectors, but I haven't found anything helpful.

推荐答案

您正在寻找的是Java 8中添加的Java Stream框架.

What you're looking for is the Java Stream framework added in Java 8.

Stream 类具有3个reduce方法:

• T reduce(T identity, BinaryOperator<T> accumulator)
• 第二个reduce方法与您的示例匹配，但需要相同的结果类型.对于不同的结果类型，您需要使用第三个reduce方法，该方法需要一个额外的combiner方法，因为它需要支持并行处理.

  The second reduce method matches your example, but requires same result type. For different result type, you need to use the third reduce method, which requires an extra combiner method, since it needs to support parallel processing.

  它也有2个collect方法:

  • 第一个collect方法是最常用的方法，与

    The first collect method is the most commonly used one, when used in combination with the Collectors factory class.

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