正则表达式:?:表示法(问号和冒号表示法) [英] Regex: ?: notation (Question mark and colon notation)

问题描述

我有以下Java正则表达式，我没有写，并且正在尝试修改:

I have the following Java regex, which I didn't write and I am trying to modify:

^class-map(?:(\\s+match-all)|(\\s+match-any))?(\\s+[\\x21-\\x7e]{1,40})$
           ^                                 ^

类似于这一个.

请注意第一个问号.这是否意味着该组是可选的?相应的)后面已经有一个问号.冒号在正则表达式中有特殊含义吗?

Note the first question mark. Does it mean that the group is optional? There is already a question mark after the corresponding ). Does the colon have a special meaning in regex?

regex可以很好地编译，并且已经有JUnit测试显示它如何工作.只是我对为什么第一个问号和冒号存在感到困惑.

The regex compiles fine, and there are already JUnit tests that show how it works. It's just that I'm a bit confused about why the first question mark and colon are there.

推荐答案

(?:启动一个非捕获组.除非您在使用后从正则表达式中检索组，否则它与(没有什么不同.请参阅什么是非捕获组? .

(?: starts a non-capturing group. It's no different to ( unless you're retrieving groups from the regex after use. See What is a non-capturing group? What does a question mark followed by a colon (?:) mean?.

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