public static String withFirst(String input, Function<Character, String> callback) {
        if (input == null) {
            return null;
        } else if (input.length() == 0) {
            return "";
        } else {
            return String.join("",
                callback.apply(input.charAt(0)),
                input.subSequence(1, input.length())
            );
        }
    }
Does something with the first character in the specified String.

@param input The String.
@param callback The something.
@return The new String.
common-parent/codegen/src/main/java/com/speedment/common/codegen/util/Formatting.java