code: public static int getOccurrenceCount(String expr, String str)
      {
          int ret = 0;
          Pattern p = Pattern.compile(expr);
          Matcher m = p.matcher(str);
          while(m.find()) 
              ++ret;
          return ret;
      }
docs: Returns the number of occurrences of the substring in the given string.
  @param expr The string to look for occurrences of
  @param str The string to search
  @return The number of occurences