Stream方式获取第一个元素匹配布尔值的索引

Stream Way to get index of first element matching boolean(Stream方式获取第一个元素匹配布尔值的索引)

问题描述

我有一个List<Users>.我想使用特定用户名获取流中(第一个)用户的索引.我不想实际上要求 User 是 .equals() 到一些描述的 User，只是为了拥有相同的用户名.

I have a List<Users>. I want to get the index of the (first) user in the stream with a particular username. I don't want to actually require the User to be .equals() to some described User, just to have the same username.

我可以想到一些丑陋的方法来做到这一点(迭代和计数)，但感觉应该有一个很好的方法来做到这一点，可能是通过使用 Streams.到目前为止，我拥有的最好的是:

I can think of ugly ways to do this (iterate and count), but it feels like there should be a nice way to do this, probably by using Streams. So far the best I have is:

int index = users.stream()
    .map(user -> user.getName())
    .collect(Collectors.toList())
    .indexOf(username);

这不是我写过的最糟糕的代码，但也不是很好.它也不是那么灵活，因为它依赖于一个类型的映射函数，该函数具有描述您要查找的属性的 .equals() 函数；我宁愿有一些可以用于任意 Function<T, Boolean>

Which isn't the worst code I've ever written, but it's not great. It's also not that flexible, as it relies on there being a mapping function to a type with a .equals() function that describes the property you're looking for; I'd much rather have something that could work for arbitrary Function<T, Boolean>

有人知道怎么做吗?

推荐答案

java中偶尔没有pythonic zipWithIndex.所以我遇到了这样的事情:

Occasionally there is no pythonic zipWithIndex in java. So I came across something like that:

OptionalInt indexOpt = IntStream.range(0, users.size())
     .filter(i -> searchName.equals(users.get(i)))
     .findFirst();

您也可以使用 protonpack 库中的 zipWithIndex

Alternatively you can use zipWithIndex from protonpack library

注意

如果 users.get 不是恒定时间操作，该解决方案可能会很耗时.

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