如何在正则表达式中转义字符

Question

When I use the following code I've got an error:

 Matcher matcher = pattern.matcher("/Date\(\d+\)/");

The error is :

invalid escape sequence (valid ones are \\b \\t \\n \\f \\r \\" \\' \\\\ )

I have also tried to change the value in the brackets to ('/Date\\(\\d+\\)/') ; without any success.

How can i avoid this error?

Answer 1

You need to double-escape your \\ character, like this: \\\\ .

Otherwise your String is interpreted as if you were trying to escape ( .

Same with the other round bracket and the d.

In fact it seems you are trying to initialize a Pattern here, while pattern.matcher references a text you want your Pattern to match.

Finally, note that in a Pattern , escaped characters require a double escape, as such:

\\(\\d+\\)

Also, as Rohit says, Pattern s in Java do not need to be surrounded by forward slashes ( / ).

In fact if you initialize a Pattern like that, it will interpret your Pattern as starting and ending with literal forward slashes.

Here's a small example of what you probably want to do:

// your input text
String myText = "Date(123)";
// your Pattern initialization
Pattern p = Pattern.compile("Date\\(\\d+\\)");
// your matcher initialization
Matcher m = p.matcher(myText);
// printing the output of the match...
System.out.println(m.find());

Output:

true

Answer 2

Your regex is correct by itself , but in Java, the backslash character itself needs to be escaped.

Thus, this regex:

/Date\(\d+\)/

Must turn into this:

/Date\\(\\d+\\)/

One backslash is for escaping the parenthesis or d . The other one is for escaping the backslash itself.

The error message you are getting arises because Java thinks you're trying to use \\( as a single escape character, like \\n , or any of the other examples. However, \\( is not a valid escape sequence, and so Java complains.

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In addition, the logic of your code is probably incorrect. The argument to matcher should be the text to search (for example, "/Date(234)/Date(6578)/"), whereas the variable pattern should contain the pattern itself. Try this:

String textToMatch = "/Date(234)/Date(6578)/";
Pattern pattern = pattern.compile("/Date\\(\\d+\\)/");
Matcher matcher = pattern.matcher(textToMatch);

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Finally, the regex character class \\d means "one single digit." If you are trying to refer to the literal phrase \\\\d , you would have to use \\\\\\\\d to escape this. However, in that case, your regex would be a constant, and you could use textToMatch.indexOf and textToMatch.contains more easily.

Answer 3

要在Java中转义正则表达式，还可以使用Pattern.quote()