Java REGEX匹配字符串中的确切位数 [英] Java REGEX to match an exact number of digits in a string

问题描述

我试图在问题历史中找到我的问题的答案，但他们只是回来了一千多个，在扫描了几十个匹配的答案之后我放弃了。
所以这是我的问题。

I tried to find the answer to my problem in the questions history but they just come back in more than one thousand and after scanning through a few tens of matching answers I gave up. So here is my problem.

我希望能够在字符串中找到正好六位数的第一个序列。
给定字符串
一些文本987654321和一些其他文本123456和一些其他文本再次654321和更多文本到底
我想找到与123456序列匹配的正则表达式。

I want to be able to find the first sequence of exactly six digits in a string. Given the string "Some text 987654321 and some more text 123456 and some other text again 654321 and more text in the end" I want to find the regex that will match the 123456 sequence.

我是regex的新手，关于它如何运作的简短解释会有很大的帮助。

I am new to regex and a short explanation about how it works will help a lot.

谢谢提前

推荐答案

您可以使用模式（？<！\ d）\ d {6}（？！\ d），表示一个字符串位置，前面没有数字;后跟正好六位数字;后跟一个字符串位置，后面没有一个数字。 （符号（？<！...），称为负后观断言，表示前面没有 ... 。符号（？！...），称为否定先行断言，表示未跟随 ... 。符号 \d 表示数字。符号 {n} 表示 n 次，例如 \d {6} 表示六位。）

You can use the pattern (?<!\d)\d{6}(?!\d), which means "a string-position that is not preceded by a digit; followed by exactly six digits; followed by a string-position that is not followed by a digit". (The notation (?<!...), known as a negative lookbehind assertion, means "not preceded by ...". The notation (?!...), known as a negative lookahead assertion, means "not followed by ...". The notation \d means a digit. The notation {n} means "n times", so that e.g. \d{6} means "six digits".)

这可能如下所示：

final String number;
{
    final Matcher m = Pattern.compile("(?<!\\d)\\d{6}(?!\\d)").matcher(input);
    if(m.find())
        number = m.group(); // retrieve the matched substring
    else
        number = null; // no match found
}

注意：以前的这个答案的版本建议使用单词边界， \ b ;但是你的一条评论表明，繁体中文字符可能会紧跟在前面或后面，这些字符被认为是单词字符（因此不会触发单词边界），所以我改变了它。

Note: a previous version of this answer suggested the use of word boundaries, \b; but one of your comments suggests that the digits might be immediately preceded or followed by Traditional Chinese characters, which are considered word characters (and therefore wouldn't trigger a word boundary), so I've changed that.

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