关于java的正则表达式的一些疑惑……

Posted 2023-03-11

我看的程序有这样一个正则表达式
String regex = "\\w+([-+.]\\w+)*@\\w+([-.]\\w+)*\\.\\w+([-.]\\w+)*";
别的我都能看懂，只要是这个“.” "."在正则表达式里是全部的意思，
“\.”不就是说明了它有特殊的含义吗？为什么要加俩个“\\”了？？
而“\w”在正则表达式里表示用于标识符的字符，为什么只加一个“\”??
API 里是这样写的
预定义字符类
. 任何字符（与行结束符可能匹配也可能不匹配）
\d 数字：[0-9]
\D 非数字： [^0-9]
\s 空白字符：[ \t\n\x0B\f\r]
\S 非空白字符：[^\s]
\w 单词字符：[a-zA-Z_0-9]
\W 非单词字符：[^\w]

为什么". " 比"\w"用时多一个“\”这个呢？！说到底，我是不懂斜杠的真正的用法，请您帮忙看看！谢谢了！
按照你说的，那么在时间里面为什么输出这样的格式2009/04/11 时，字符串是这样写的SimpleDateFormat sdf1 = new SimpleDateFormat("yy/MM/dd");这里是一个/呀？！我真的不懂，帮忙看看，谢谢！！！

你说的“.” 你说/是转义的么那么“/.”不就把“.”转义了吗？怎么还要俩个//了？！不懂，谢谢了！！！帮忙看看！

在JAVA中\是转义符，有些字符表示了一些特殊的用法，比如n，如果是\n，就把n转义成了特殊字符,\n在JAVA中就表示换行。

正则中，\d表示数字，\d中的\是真实的\,而到了JAVA的字符串中表示转义符，那怎么办呢？那我们就在\d前面再加一个\，再转义一次，就把原来的转义符取消了，就表示真正的\了。

.在正则中表示任何字符除了.本身，如何表示.本身呢？就需要在.前面加\，然而由于上述的原因，所以又需多加一个\。当你看JAVA写的正则时，你就把\\当一个\理解就可以了。

你可以理解为双重\,如果在正则中有个\的，在JAVA中，就把他变成两个\\，就是JAVA把他多加一层。 参考技术A ,wholesale gucci hoodies 2 Coco Chanel Biography y
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