提供正则表达式时，Java中的String.split（）方法到底如何工作？

Question

我正在为OCPJP考试做准备，并且遇到了以下示例：

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);
   }
}

这段代码显示为16。我期待的是类似no_of_characters +1的内容。有人可以解释一下，在这种情况下split（）方法实际上是做什么的？我就是不明白…

Answer 1

它"\\S"在正则表达式引擎中表示\S非空白字符的每个字符上进行拆分。

因此，让我们尝试分割"x x"非空白（\S）。由于此正则表达式可以用一个字符进行匹配，因此可以对其进行迭代以标记拆分的位置（我们将使用竖线|进行表示）。

• 是'x'一个非空白？是的，让我们标记一下| x
• 是' '一个非空白？不，所以我们保持原样
• 是最后一个'x'非空白吗？是的，让我们标记一下| |

因此，作为结果，我们需要在开始和结束时拆分字符串，这最初会给我们结果数组

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

但是由于删除了结尾的 空字符串 ，结果将是

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

因此split返回["", " "]仅包含两个元素的数组。

顺便说一句。要关闭删除最后一个空字符串的操作，您需要使用split(regex,limit)limit的负值，例如split("\\S",-1)。

现在回到您的示例。如果您有数据，则将每个

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

意思是

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

所以这代表这个数组

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

但是由于""删除了结尾的空字符串（如果它们的存在是由split引起的-
有关更多信息，请访问：混淆String.split的输出）

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

您得到的结果数组仅包含以下部分：

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

正好是16个元素