private static String REGEX = "(r)(\\d*)(c)(\\d*)";
   private static String INPUT = "r1c12+23*4/r4c5";//"aabfooaabfooabfoob";
   private static String REPLACE = "F";
     ....
 Pattern p = Pattern.compile(REGEX);
      Matcher m = p.matcher(INPUT);
      StringBuffer sb = new StringBuffer();
      while(m.find()){
          System.out.println(m.group());
          System.out.println(m.group(1));
          System.out.println(m.group(2));
          System.out.println(m.group(3));
          System.out.println(m.group(4));          
         m.appendReplacement(sb,REPLACE);
      }
      m.appendTail(sb);
      System.out.println(sb.toString());