String.replaceAll troubles with regEx

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sugapablo@hotmail.com - 17 Apr 2006 15:38 GMT

I'm trying to replace instances of a single quote "'" with a backslash
single quote "\'".

But I can't get it to work with the replaceAll function.
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html#replaceAll(java.la
ng.String,%20java.lang.String)

I'm trying String.replaceAll("'","\\'")

What am I doing wrong? Even when I put a "C" in the first argument, it
only replaces it a single quote. Not a backslash and then a single
quote.

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Knute Johnson - 17 Apr 2006 16:25 GMT

> I'm trying to replace instances of a single quote "'" with a backslash
> single quote "\'".
[quoted text clipped - 7 lines]
> only replaces it a single quote. Not a backslash and then a single
> quote.

replaceAll("'","\\\\'");

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Knute Johnson
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Oliver Wong - 17 Apr 2006 16:41 GMT

You need something like replaceAll("'","\\\\'"), with 4 blackslashes.
There's two layers of escaping going on: One in Java, and one in the RegExp
engine. See
http://groups.google.com/group/comp.lang.java.programmer/msg/3fd11f7fb586e837
for an explanation. When you write "\\\\'" in Java, the in-memory string
becomes "\\'", and then the RegExp engine treats that as "\'".

- Oliver

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Chris Smith - 17 Apr 2006 16:51 GMT

> > I'm trying String.replaceAll("'","\\'")
>
> You need something like replaceAll("'","\\\\'"), with 4 blackslashes.
> There's two layers of escaping going on: One in Java, and one in the RegExp
> engine.

The subtlety worth pointing out here is that even the second parameter
to String.replaceAll is NOT a plain String. The API docs for
String.replaceAll are far from clear in pointing this out. It is
pointed out in the API docs for Matcher.replaceAll if you follow links
that far, and Java 1.5 introduces a method called
Matcher.quoteReplacement that can make this clearer than doing the
quoting by hand:

s.replaceAll(Pattern.quote("'"),
Matcher.quoteReplacement("\\'"));

This is a classic example of poor API design, and it's confused
thousands of people and cost thousands of man-hours of effort.

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Knute Johnson - 17 Apr 2006 19:45 GMT

>>> I'm trying String.replaceAll("'","\\'")
>>>
[quoted text clipped - 15 lines]
> This is a classic example of poor API design, and it's confused
> thousands of people and cost thousands of man-hours of effort.

It sure is and it sure has!

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Knute Johnson
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Roedy Green - 17 Apr 2006 21:26 GMT

On Mon, 17 Apr 2006 11:45:32 -0700, Knute Johnson
<nospam@ljr-2.frazmtn.com> wrote, quoted or indirectly quoted someone
who said :

>> s.replaceAll(Pattern.quote("'"),
>> Matcher.quoteReplacement("\\'"));
[quoted text clipped - 3 lines]
>
>It sure is and it sure has!

if we had to do this over, i think you would have named methods:

replaceFirst, replaceAll, replacePatterns

or perhaps

replaceChars, replaceString, replaceStrings, replacePatterns

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http://mindprod.com Java custom programming, consulting and coaching.

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Chris - 19 Apr 2006 17:50 GMT

> if we had to do this over, i think you would have named methods:
>
[quoted text clipped - 3 lines]
>
> replaceChars, replaceString, replaceStrings, replacePatterns

I think I would have done replaceAll(String, String) and also a
replaceAll(Pattern, String).

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MindIQ Corporation

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Roedy Green - 17 Apr 2006 20:10 GMT

>I'm trying to replace instances of a single quote "'" with a backslash
>single quote "\'".

you are likely having problem with either regex or Java quoting.

see http://mindprod.com/jgloss/regex.html#QUOTING

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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String.replaceAll troubles with regEx

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