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Asked: 2026-06-09T09:00:03+00:00

I’m trying to write a regular expression in Java which removes all non-alphanumeric characters

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I’m trying to write a regular expression in Java which removes all non-alphanumeric characters from a paragraph, except the spaces between the words.

This is the code I’ve written:

paragraphInformation = paragraphInformation.replaceAll("[^a-zA-Z0-9\s]", "");

However, the compiler gave me an error message pointing to the s saying it’s an illegal escape character. The program compiled OK before I added the \s to the end of the regular expression, but the problem with that was that the spaces between words in the paragraph were stripped out.

How can I fix this error?

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1 Answer

  1. Editorial Team

    You need to double-escape the \ character: "[^a-zA-Z0-9\\s]"

    Java will interpret \s as a Java String escape character, which is indeed an invalid Java escape. By writing \\, you escape the \ character, essentially sending a single \ character to the regex. This \ then becomes part of the regex escape character \s.

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