当提供正则时，Java中的string.split()方法究竟如何工作

Question

我正在为OCPJP考试做准备，我遇到了以下示例：

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);
   }
}

此代码打印16.我期望像no_of_characters 1。我只是不明白...

Answer 1

它在Regex引擎中代表S非Whitespace字符的每个"\S"上分配。

因此，让我们尝试在非Whitespace（S）上拆分"x x"。由于可以通过一个字符匹配此正则表达式，让迭代在它们上标记拆分的位置（我们将使用管道|为此）。

• 'x'非Whitespace吗？是的，让我们标记它| x
• ' '非Whitespace吗？不，所以我们将其保留为
• 最后一个 'x'是非惠特太空？是的，让我们标记它| |

因此，由于我们需要在开始和结束时分开字符串，这最初为我们提供结果数组

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

，由于拖延空字符串被删除，结果将为

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

因此，拆分返回数组["", " "]仅包含两个元素。

顺便说一句。要关闭卸下最后一个空字符串，您需要使用 split(regex,limit)，其负值为 split("\S",-1)。

---

现在让我们回到您的示例。如果您的数据，您都在

中分配

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

这意味着

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

所以这代表此数组

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

但是，由于拖动空字符串""被删除（如果它们的存在是由拆分引起的 - 更多信息，请访问：cline.string.split的输出）

）

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

您正在获得结果数组，仅包含此部分：

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

正好是16个元素。