Java使用负前瞻将字符串拆分为字符 [英] Java splitting a string into characters using negative look-ahead

问题描述

我试图将字符串拆分为字符数组字符串，问题是 .split（）也返回一个空元素。 （test）。split 将返回 [，t，e，s，t] 。

I was trying to split a string into an array of characters string, the problem is that .split() returns an empty element also. ("test").split would return ["","t","e","s","t"].

此问题中的解决方案将字符串拆分为字符串数组解决了问题（使用 .split（（？！^）））。

The solution in this question Split string into array of character strings solves the problem ( using .split("(?!^)") ).

但是我仍然无法理解为什么会这样，我不会使用一段我无法理解的代码只是因为它得到了工作完成。

However I still cannot understand why this works, and i'm not going to use a piece of code which i cannot understand just because it gets the job done.

我读过这两页 http://www.regular-expressions.info/lookaround.html 和 http://ocpsoft.org/opensource/guide-to-regular-expressions-in-java-part-2/ 关于负面预测仍然无法理解。有人可以澄清这个吗？

I've read these two pages http://www.regular-expressions.info/lookaround.html and http://ocpsoft.org/opensource/guide-to-regular-expressions-in-java-part-2/ about negative look-ahead and still cannot understand. Can someone clarify this?

推荐答案

使用（test）。split（）会将字符串拆分到字符前的每个位置，从而产生 [，t，e，s，t] ，因为第一次拆分（在 t 之前）将导致空条目。

using ("test").split() will split the string at EVERY position before a character, resulting in ["", "t", "e", "s", "t"], because the first split (in front of t) will cause an empty entry.

此正则表达式（（？！^））的意思是：在每个字符处拆分字符串，其中不是行开头（^）是前一个字符 *：

This regex ("(?!^)") does mean: Split the string at every Character, where NOT the line-start (^) is the previous character*:

你的字符串基本上看起来（对于Regex引擎）是这样的： ^ test $
所以，正则表达式将执行每个拆分，除了在第一个 t 之前的拆分，因为它匹配 ^ - 并且它当前位置前面的字符是 ^ （字符串/行开始）时，不应拆分。

Your string basically looks (for the Regex Engine) like this: ^test$ So, the regex will perform EVERY split, except the split before the first t, because there it matches the ^ - and it should NOT split, when the char in front of the current position is the ^ (String / Line-Start).

* actualley ^ 不是一个字符，这就是为什么你在 $ 之前没有另一个分割 - 它们是只是元字符 - 所以t o说。

*actualley the ^ is not a character, thats why you dont have another split before the $ - they are just meta-characters - so to say.

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