Error in String.replaceAll() function

Question

I am trying the following code:-

String x = "asdfg/dgws";
x.replaceAll("/", "\\");

But this is failing. This is giving me the following error message:-

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 1
    at java.lang.String.charAt(Unknown Source)
    at java.util.regex.Matcher.appendReplacement(Unknown Source)
    at java.util.regex.Matcher.replaceAll(Unknown Source)
    at java.lang.String.replaceAll(Unknown Source)
    at com.jai.SecLargest.main(SecLargest.java:13)

I am not able to figure out why this exception is coming?

Jon Skeet · Accepted Answer · 2012-06-04 07:32:58Z

String.replaceAll ends up using (or being equivalent to using) Matcher.replaceAll, which includes this in the documentation:

Note that backslashes () and dollar signs ($) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string. Dollar signs may be treated as references to captured subsequences as described above, and backslashes are used to escape literal characters in the replacement string.

While you could escape the backslash as per AlexR's answer, I would strongly recommend that you use replace instead:

String y = x.replace('/', '\\');

That's a lot clearer, IMO - don't use replaceAll unless you're really trying to express a pattern via regular expressions.

Also note that as written your code would be a no-op anyway; strings are immutable in Java, so the replaceAll method (and similar ones) return a reference to a new string with the modificiations made.

AlexR · Accepted Answer · 2012-06-04 07:30:39Z

8

You should say x.replaceAll("/", "\\\\");

Back slash \ must be escaped twice: once of regular expressions engine and once for java itself.

answered Jun 4, 2012 at 7:30

AlexR

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Comments

MicNeo · Accepted Answer · 2015-12-07 16:05:50Z

0

You can also use quoteReplacement() method, in case you really need a regex.

answered Dec 7, 2015 at 16:05

MicNeo

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