Java RegEx 负面回顾 [英] Java RegEx negative lookbehind

问题描述

我有以下 Java 代码:

I have the following Java code:

Pattern pat = Pattern.compile("(?<!function )\\w+");
Matcher mat = pat.matcher("function example");
System.out.println(mat.find());

为什么 mat.find() 返回 true?我使用了负向后视，example 前面是 function.不应该被丢弃吗?

Why does mat.find() return true? I used negative lookbehind and example is preceded by function. Shouldn't it be discarded?

推荐答案

看看它匹配了什么:

public static void main(String[] args) throws Exception {
    Pattern pat = Pattern.compile("(?<!function )\\w+");
    Matcher mat = pat.matcher("function example");
    while (mat.find()) {
        System.out.println(mat.group());
    }
}

输出:

function
xample

所以它首先找到function，它前面没有function".然后它找到 xample 前面是 function e，因此不是function".

So first it finds function, which isn't preceded by "function". Then it finds xample which is preceded by function e and therefore not "function".

大概您希望模式匹配整个文本，而不仅仅是在文本中查找匹配.

Presumably you want the pattern to match the whole text, not just find matches in the text.

您可以使用 Matcher.matches() 执行此操作，也可以更改模式以添加开始和结束锚点:

You can either do this with Matcher.matches() or you can change the pattern to add start and end anchors:

^(?<!function )\\w+$

我更喜欢第二种方法，因为它意味着模式本身定义了它的匹配区域，而不是由它的用法定义的区域.不过，这只是个人喜好问题.

I prefer the second approach as it means that the pattern itself defines its match region rather then the region being defined by its usage. That's just a matter of preference however.

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