public class HelloWorld {

    public static void main(String[] args) {
        final var nameParts = (args.length == 0) ? new String[]{"world"} : args;
        System.out.println(formatMessageWithName(nameParts));
    }

    private static String formatMessageWithName(final String[] nameParts) {
        return "Hello " + String.join(" ", nameParts) + "!";
    }

}