Regular expression: dollar sign problem????

Question

Hi:
Let's say I have a String like this:"add %a, %a, %b". I want to replace every "%a" with a "$t0". So I do the following:
public class testing {
public static void main(String[] args)
throws Exception {
Pattern p = Pattern.compile("%a");
Matcher m = p.matcher("add %a, %a, %b");
StringBuffer sb = new StringBuffer();
boolean result = m.find();
while(result) {
m.appendReplacement(sb, "$t0");
result = m.find();
m.appendTail(sb);
System.out.println(sb.toString());
However, I got a group reference exception. It seems like dollar sign means group of words. How can I insert a dollar sign into a String without causing this excpetion?
Thanx a lot

Answer 1

From the api documentation for [url http://java.sun.com/j2se/1.4/docs/api/java/util/regex/Matcher.html#appendReplacement(java.lang.StringBuffer, java.lang.String)]Matcher.appendReplacement(java.lang.StringBuffer, java.lang.String):
The replacement string may contain references to subsequences captured during the
previous match: Each occurrence of $g will be replaced by the result of evaluating
group(g). If the second group matched the string "foo", for example, then passing
the replacement string "$2bar" would cause "foobar" to be appended to the string
buffer. A dollar sign ($) may be included as a literal in the replacement string by
preceding it with a backslash (\$).So, use m.appendReplacement(sb, "\\$t0") instead.