String uniqueCharacters(String text) that creates and returns a String that contains each character that occurs in the given text, so that each character is included in this result only once. These characters must occur in the result in the exact same order as they first occur in the original string. For example, when called with argument Hello there, world!, this method would return Helo thr,wd! (Again for efficiency, you should use a StringBuilder inside the method to build up the result.)