private final static Pattern formatPattern = Pattern.compile("\\{(\\d+)\\}");
   public static String format(String string, Object... args) {
       Matcher matcher = formatPattern.matcher(string);
       StringBuffer builder = new StringBuffer();

       while (matcher.find()) {
           int index = Integer.parseInt(matcher.group(1));

           if (index < 0 || index > args.length) {
               continue;
           }

           matcher.appendReplacement(builder, args[index].toString());
       }
       matcher.appendTail(builder);

       return builder.toString();
   }

System.out.println(format("Ciao {0}, come {1}?", "Mondo", "stai"));