Name: nt126004 Date: 01/14/2003


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 :
SunOS 5.7 Generic_106542-22 i86pc i386 i86p



A DESCRIPTION OF THE PROBLEM :
Instead of keeping the cleansiness and robustness of Java
regex vs. Perl programming, this method contains a "trap",
namely the coding of capture groups in the replacement
string.
appendReplacement is meant to replace with calculated
replacement strings (as opposed to hand-typed) - otherwise
methods like replaceAll or replaceFirst should be used.
The benefit of using the Perl-like technique of the $g
shortcut is merely to save a little writing (namely
replacing $2 by " + matcher.group(2) + ").

The drawback and complication (I call it a trap) you have
introduced in this method disparages the robustness of the
java.utils.regex package: namely, in a calculated
replacement string, one must parse for $ characters and
escape them - that's a special, error-prone treatment,
likely to be forgotten and to provoke ununderstandable
runtime bugs (as the replacement string might change every
time the program runs, and sometimes happen to contain a $
sign).


EXPECTED VERSUS ACTUAL BEHAVIOR :
The $g feature is a non-feature: I claim the only benefit
is to save a few characters' typing. It however is the
source of bugs 4497669 4618713 4621239 4684543 4509697.

My proposal is to abandon this feature.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
String regex = "cat";
CharSequence input = "one cat two cats in the yard";
Pattern p = Pattern.compile(regex);
Matcher matcher = p.matcher(input);
StringBuffer sb = new StringBuffer();

while (matcher.find()) {
    matcher.appendReplacement(sb, replacementMethod(matcher.group)));
    }
    matcher.appendTail(sb);
---------- END SOURCE ----------

CUSTOMER WORKAROUND :
Either you can parse and replace all $ in the replacement
string by \$ before replacing, or you can program
the "clean" ($g-feature-less) appendReplacement yourself:

            int append = 0;
            while (matcher.find()) {
                sb.append(input.subSequence(append,
matcher.start()));
                append = matcher.end();
                sb.append(replacementMethod(matcher.group
()));
            }
            sb.append(input.subSequence(append, input.length
()));
(Review ID: 178859)
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