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Asked: 2026-05-30T20:30:09+00:00

I can’t figure out why the following code doesn’t behave as expected Hello/You/There.replaceAll(/, \\/);

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I can’t figure out why the following code doesn’t behave as expected

"Hello/You/There".replaceAll("/", "\\/");
  • Expected output: Hello\/You\/There
  • Actual output: Hello/You/There

Do I need to escape forward slashes? I didn’t think so but I also tried the following against my will … didn’t work

"Hello/You/There".replaceAll("\\/", "\\/");

In the end I realized I don’t need a regular expression and I can just use the following, which doesn’t create a regular expression

"Hello/You/There".replace("/", "\\/");

However, I’d still like to understand why my first example doesn’t work.

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1 Answer

  1. Editorial Team

    The problem is actually that you need to double-escape backslashes in the replacement string. You see, "\\/" (as I’m sure you know) means the replacement string is \/, and (as you probably don’t know) the replacement string \/ actually just inserts /, because Java is weird, and gives \ a special meaning in the replacement string. (It’s supposedly so that \$ will be a literal dollar sign, but I think the real reason is that they wanted to mess with people. Other languages don’t do it this way.) So you have to write either:

    "Hello/You/There".replaceAll("/", "\\\\/");

    or:

    "Hello/You/There".replaceAll("/", Matcher.quoteReplacement("\\/"));

    (Using java.util.regex.Matcher.quoteReplacement(String).)

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