模式中的冗余转义字符 [英] Redundant escape character in Pattern

问题描述

我正在尝试以下代码并且它打印为false。
我原本预计这会打印出来。
另外，Pattern.Compile（）statemenet给出了一个警告'冗余转义字符'。
有人可以帮助我，为什么这不会返回真实，为什么我会看到警告。

I am trying out the following code and it's printing false. I was expected that this would print true. In addition , the Pattern.Compile() statemenet , gives a warning 'redundant escape character'. Can someone please help me as to why this is not returning true and why do I see a warning.

public static void main(String[] args) {
    String s = "\\n";
    System.out.println(s);

    Pattern p = Pattern.compile("\\\n");
    Matcher mm = p.matcher(s);
    System.out.println(mm.matches());
}

推荐答案

s =\\ n表示您为变量 s n c $ c>，它包含两个字符的序列， \ 和 n 。

The s="\\n" means you assign a backslash and n to the variable s, and it contains a sequence of two chars, \ and n.

Pattern.compile（\\\ n）表示你定义一个正则表达式模式 \ n 匹配换行符。因此，此模式将与变量 s 中的字符串不匹配。

The Pattern.compile("\\\n") means you define a regex pattern \n that matches a newline char. Thus, this pattern won't match the string in variable s.

冗余转义警告与事实上你在C字符串文字中使用三个反斜杠：两个反斜杠定义一个文字反斜杠，第三个是冗余的，即有一个文字 \ 然后换行转义序列\ n，这意味着文字反斜杠（在文字中用2个反斜杠定义）是多余的，可以删除。

The redundant escape warning is related to the fact you are using triple backslash in the C string literal: the two backslashes define a literal backslash and the third one is redundant, i.e. there is a literal \ and then a newline escape sequence "\n", and that means the literal backslash (defined with 2 backslashes in the literal) is redundant and can be removed.

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