当提供正则表达式时，Java中的String.split（）方法究竟是如何工作的？ [英] How exactly does String.split() method in Java work when regex is provided?

问题描述

我正在准备OCPJP考试，我遇到了以下示例：

I'm preparing for OCPJP exam and I ran into the following example:

class Test {
   public static void main(String args[]) {
      String test = "I am preparing for OCPJP";
      String[] tokens = test.split("\\S");
      System.out.println(tokens.length);
   }
}

此代码打印16.我期待像no_of_characters这样的东西+ 1.有人可以解释一下，split（）方法在这种情况下实际上做了什么？我只是不明白......

This code prints 16. I was expecting something like no_of_characters + 1. Can someone explain me, what does the split() method actually do in this case? I just don't get it...

推荐答案

它分裂在每个\\ S在正则表达式引擎中代表 \S 非空白字符。

It splits on every "\\S" which in regex engine represents \S non-whitespace character.

因此，我们尝试在非空格上拆分xx（ \ S ）。由于这个正则表达式可以匹配一个字符，让迭代它们来标记拆分的位置（我们将使用管道 | ）。

So lets try to split "x x" on non-whitespace (\S). Since this regex can be matched by one character lets iterate over them to mark places of split (we will use pipe | for that).

• 是'x'非空白？是的，所以让我们标记 | x


• 是''非空白？不，所以我们保持原样


• 是最后一个'x'非空白？是的，所以让我们标记 | |

• is 'x' non-whitespace? YES, so lets mark it | x
• is ' ' non-whitespace? NO, so we leave it as is
• is last 'x' non-whitespace? YES, so lets mark it | |

因此我们需要在开始和结束时拆分我们的字符串，这最初会给我们带来结果数组

So as result we need to split our string at start and at end which initially gives us result array

["", " ", ""]
   ^    ^ - here we split

但由于删除了尾随空字符串，结果将是

But since trailing empty strings are removed, result would be

[""," "]     <- result
        ,""] <- removed trailing empty string

所以split返回数组 [，] 其中只包含两个元素。

so split returns array ["", " "] which contains only two elements.

BTW。要关闭删除最后一个空字符串，您需要使用 split（正则表达式，限制），其值为负值，如 split（\\ S ，-1）。

BTW. To turn off removing last empty strings you need to use split(regex,limit) with negative value of limit like split("\\S",-1).

现在让我们回到你的例子。如果您的数据是分裂的每一个

Now lets get back to your example. In case of your data you are splitting on each of

I am preparing for OCPJP
| || ||||||||| ||| |||||

这意味着

 ""|" "|""|" "|""|""|""|""|""|""|""|""|" "|""|""|" "|""|""|""|""|""

所以这代表了这个数组

[""," ",""," ","","","","","","","",""," ","",""," ","","","","",""]  

但由于尾随空字符串被删除（如果它们的存在是由分裂引起的 - 更多在信息：输出href=\"https://stackoverflow.com/questions/25056607/confusing-output-from-string-split/25058091#25058091\">混淆）

but since trailing empty strings "" are removed (if their existence was caused by split - more info at: Confusing output from String.split)

[""," ",""," ","","","","","","","",""," ","",""," ","","","","",""]  
                                                     ^^ ^^ ^^ ^^ ^^

你得到的结果数组只包含这部分：

you are getting as result array which contains only this part:

[""," ",""," ","","","","","","","",""," ","",""," "]  

这是exa 16个元素。

which are exactly 16 elements.

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