当提供正则表达式时,Java中的String.split()方法究竟是如何工作的?
我正在准备OCPJP考试,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); } }
这段代码打印16.我期待像no_of_characters + 1这样的东西。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……
它在每个"\\S"
上分裂,在正则表达式引擎中代表\S
非空白字符。
所以让我们尝试在非空格( \S
)上拆分"xx"
。 由于这个正则表达式可以匹配一个字符,让迭代它们来标记分割的位置(我们将使用管道|
为此)。
- 是
'x'
非空白? 是的,所以让我们标记它| x
- 是
' '
非空白? 不,所以我们保持原样 - 是最后
'x'
非空白? 是的,所以让我们标记它| |
因此,我们需要在开始和结束时拆分我们的字符串,最初给出结果数组
["", " ", ""] ^ ^ - here we split
但是由于尾随空字符串被删除,结果将是
[""," "] <- result ,""] <- removed trailing empty string
所以split返回array ["", " "]
,它只包含两个元素。
BTW。 要关闭删除最后一个空字符串,您需要使用split(regex,limit)
和split(regex,limit)
负值,如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
I am preparing for OCPJP | ||
||
意思是
""|" "|""|" "|""|""|""|""|""|""|""|""|" "|""|""|" "|""|""|""|""|""
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 – 更多信息在: 混淆String.split的输出 )
[""," ",""," ","","","","","","","",""," ","",""," ","","","","",""] ^^ ^^ ^^ ^^ ^^
你得到的结果数组只包含这部分:
[""," ",""," ","","","","","","","",""," ","",""," "]
这正是16个元素。