String的Java Regex以数字和固定长度开头 [英] Java Regex of String start with number and fixed length

问题描述

我做了一个正则表达式来检查String的长度，所有字符都是数字并以数字开头，例如123
以下是我的表达式

I made a regular expression for checking the length of String , all characters are numbers and start with number e.g 123 Following is my expression

REGEX =^123\\d+{9}$";

但它无法检查String的长度。它验证那些字符串只有它们的长度是9并从123开始。
但是如果我传递字符串1234567891它也验证它。但是我应该怎么做呢在我这边是错的。

But it was unable to check the length of String. It validates those strings only their length is 9 and start with 123. But if I pass the String 1234567891 it also validates it. But how should I do it which thing is wrong on my side.

推荐答案

就像这里已经回答的那样，最简单的方法就是删除 + ：

Like already answered here, the simplest way is just removing the +:

^123\\d{9}$

或

^123\\d{6}$

具体取决于您的需求。

你也可以使用另一种，更复杂和通用的方法，消极前瞻：

You can also use another, a bit more complicated and generic approach, a negative lookahead:

(?!.{10,})^123\\d+$

说明：

这： （？！。{10，}）是负面预测（？= 会是一个积极的表情-ahead），这意味着如果前瞻后的表达式匹配此模式，则整个字符串不匹配。大致意味着：仅当负前瞻中的模式与不匹配时，才会满足此正则表达式的条件。

This: (?!.{10,}) is a negative look-ahead (?= would be a positive look-ahead), it means that if the expression after the look-ahead matches this pattern, then the overall string doesn't match. Roughly it means: The criteria for this regular expression is only met if the pattern in the negative look-ahead doesn't match.

In在这种情况下，字符串匹配仅如果。{10} 不匹配，这意味着10个或更多字符，所以它只匹配前面的模式最多匹配9个字符。

In this case, the string matches only if .{10} doesn't match, which means 10 or more characters, so it only matches if the pattern in front matches up to 9 characters.

正向前瞻相反，只有在前瞻中的条件匹配。

A positive look-ahead does the opposite, only matching if the criteria in the look-ahead also matches.

出于好奇的缘故，将它放在这里，它比你需要的更复杂。

Just putting this here for curiosity sake, it's more complex than what you need for this.

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