捕获和非捕获模式有什么区别？ [英] What is the difference between capturing and non-capturing Pattern?

问题描述

在模式类中，它表示有两种类型的正则表达式：捕获和非捕获，但是我不明白其中的区别。

In the Pattern class it says there are two types of regex: capturing and non-capturing, but I don't understand the difference.

http://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html#special

他们有什么不同？我何时必须使用每一个？任何例子？

How are they different? When do I have to use each one? Any examples?

推荐答案

考虑一种模式，你需要在一个位置检查各种事物，例如一堆不同的两个字符模式。通常你使用 | 交替运算符：

Consider a pattern where you need to check for a variety of things in a single position, e.g a bunch of different two character patterns. Normally you use the | alternation operator:

/(ab|cd|ef)/

需要使用（）括号。但这些括号也可作为捕获组。也许你真的不想捕捉那些char序列，只是检查它们的存在，这是非捕获组发挥作用的地方：

which requires use of () brackets as well. But those brackets also act as a capturing group. Maybe you really don't want to capture those char sequences, just check for their presence, which is where the non-capturing groups come into play:

/(?:ab|cd|ef)/

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