我如何表达“:"但不以"\"开头在Java正则表达式中?

问题描述

如何在Java正则表达式中表示不以"开头?例如，我只想搜索:"，但仅当它不直接以"\"开头时才搜索.我该怎么办?

How can I express "not preceded by" in a Java regular expression? For example I would like to search for ":" but only when it is not directly preceded by "\". How can I do this?

推荐答案

使用后面是负数:

"(?<!\\\\):"

四个反斜杠的原因是:

• 反斜杠是正则表达式中的特殊字符，因此您需要正则表达式 \\ 来匹配单个反斜杠.
• 反斜杠必须在Java字符串中转义，因此上述每个反斜杠必须写为 \\ ，总共四个.

• the backslash is a special character in regular expressions so you need the regular expression \\ to match a single backslash.
• backslashes must be escaped in Java strings, so each of the above backslashes must be written as \\, giving a total of four.

示例代码:

Pattern pattern = Pattern.compile("(?<!\\\\):");
Matcher matcher = pattern.matcher("foo\\:x bar:y");
if (matcher.find()) {
    System.out.println(matcher.start());
}

输出:

10

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