Regular Expression

"a*" - zero or more a
"a+" - 1 or more a's
"[a-f]" - Any character between a and f
"[^a-cz]" - Any character which is not between a and c, and not z
"[abc]+" - 1 or more of a, b or c in a row
"abc" - character abc in a row
"a|b" - Character a or character b

Java:
java.util.regex
java.util.regex.Matcher;
java.util.regex.Pattern;

protected List getTokens(String pattern)
 {
  ArrayList tokens = new ArrayList();
  Pattern tokSplitter = Pattern.compile(pattern);
  Matcher m = tokSplitter.matcher(text);
  
  while (m.find()) {
   tokens.add(m.group());
  }
  
  return tokens;
 }