當提供正則表達式時，Java中的String.split（）方法究竟是如何工作的？

Question

我正在准備OCPJP考試，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);
   }
}

這段代碼打印16.我期待像no_of_characters + 1這樣的東西。有人可以解釋一下，split（）方法在這種情況下實際上做了什么？ 我只是不明白......

Answer 1

它在正則表達式引擎代表\\S非空白字符的每個"\\\\S"上分裂。

所以讓我們嘗試在非空格（ \\S ）上拆分"xx" 。 由於此正則表達式可以用一個字符匹配允許在它們之間迭代，以紀念分裂的地方（我們將使用管道|為該）。

• 是'x'非空白？ YES，所以讓我們將其標記| x | x
• 是' '非空白？ 不，所以我們保持原樣
• 是最后'x'非空白？ YES，所以讓我們將其標記| | | |

因此，我們需要在開始和結束時拆分我們的字符串，最初給出結果數組

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

但是由於尾隨空字符串被刪除，結果將是

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

所以split返回array ["", " "] ，它只包含兩個元素。

BTW。 要關閉刪除最后一個空字符串，您需要使用split(regex,limit)和split(regex,limit)負值，如split("\\\\S",-1) 。

---

現在讓我們回到你的例子。 如果您的數據是分裂的每一個

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

意思是

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

所以這代表了這個數組

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

但由於尾隨空字符串""被刪除（如果它們的存在是由分裂引起的 - 更多信息在： 混淆String.split的輸出 ）

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

你得到的結果數組只包含這部分：

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

這正好是16個元素。