Name: rmT116609 Date: 04/03/2003


FULL PRODUCT VERSION :
java version "1.4.1_01"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_01-b01)
Java HotSpot(TM) Client VM (build 1.4.1_01-b01, mixed mode)


FULL OPERATING SYSTEM VERSION : glibc-2.2.5-34, Linux
server 2.4.18-3 #1 Thu Apr 18 07:31:07 EDT 2002 i686
unknown, Red Hat Linux release 7.3 (Valhalla)


A DESCRIPTION OF THE PROBLEM :
The use of backslashes in the replacement string of the
java.util.Matcher class is not documented properly. The
javadoc entry of appendReplacement() mentions that a
backslash can be used to escape a $, but it doesn't
mention that if the user wants an actual backslash, they
need to use two. (In a string they need to type four.)

The following causes StringIndexOutOfBoundsException:

  String filename = "/abc/def";
  filename = filename.replaceAll("/", "\\");

because the appendReplacement() code tries to append the
character after the backslash and the charAt() dies. The
correct code is:

  filename = filename.replaceAll("/", "\\\\");

which is certainly not obvious from the documentation. Up
to you whether this is a bug in the implementation or in
the documentation.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Type in code above.
2. Run it.
3. See exception.

EXPECTED VERSUS ACTUAL BEHAVIOR :
I either expect the code to work (handle a single
backslash in the string as a single backslash) or I expect
the exception to be more meaningful
(InvalidReplacementException). The out-of-bounds
exception is a side-effect of the implementation and makes
no sense to the user. In fact, until I read the Matcher
source code, I had no idea whether the exception referred
to the regexp or in the replacement.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String
index out of range: 1
        at java.lang.String.charAt(String.java:460)
        at java.util.regex.Matcher.appendReplacement(Matcher.java:544)
        at java.util.regex.Matcher.replaceAll(Matcher.java:646)
        at java.lang.String.replaceAll(String.java:1710)
        at Test.main(Test.java:7)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
class Test {
    public static void main(String[] args) {
        String filename = "m:/abc/def/hello.mp3";

        System.out.println("Before: " + filename);
        filename = filename.replaceAll("/", "\\");
        System.out.println("After: " + filename);
    }
}

---------- END SOURCE ----------

CUSTOMER WORKAROUND :
Type four backslashes instead of two in the replacement string.
(Review ID: 180904)
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