Can I use look-behind?

[freemail <hi...@rose.freemail.ne.jp>]

In my code 
at the point
  pattern = compiler.compile("(?<=,)[0-9]+(?=,)");



 MalformedPatternException 
will occur

Can I use look-behind?
look-ahead is OK



public static void main(java.lang.String[] args) {

 int groups;
 PatternMatcher matcher;
 PatternCompiler compiler;
 Pattern pattern;
 PatternMatcherInput input;
 MatchResult result;

 compiler = new Perl5Compiler();
 matcher = new Perl5Matcher();

 StringBuffer matchResult = new StringBuffer("");

 try {
  pattern = compiler.compile("(?<=,)[0-9]+(?=,)");
  

 } catch (MalformedPatternException e) {
  System.out.println("Bad pattern.");
  System.out.println(e.getMessage());
  return;
 }

 input = new PatternMatcherInput("3,1-2223,6,7-8,9,10,11111-116166,9");

 while (matcher.contains(input, pattern)) {
  result = matcher.getMatch();

  System.out.println("Match: " + result.toString());
  matchResult.append(result.toString() + " ");

 }

 System.out.println("finally we found this string");
 System.out.println(matchResult);
}