Subtract 45 minutes from time that user provided-CodePudding

I am trying to take in a string formatted as HH:mm (24 hr format) and then subtract 45 minutes from that given time to provide the user a new time. Here is the code I have completed so far but I keep getting an Incomplete type error. Am I using the minusMinutes() incorrectly?

Edit adding error message: "Incompatible types found: 'java.time.LocalDateTime', required: 'java.lang.String': 52'

public static boolean validateTime(String timeStr)
    {
        //Regular expression logic to validate correct format:
        // ( = start of group, [01]?[0-9] time can start with 0-9,1-9, 00-09,10-19
        // | = or, 2[0-5] represents start time with 20-23, ) = end group
        //
        String regex = "([01]?[0-9]|2[0-3]):[0-5][0-9]";
        Pattern p = Pattern.compile(regex);

        //if time empty return false
        if (timeStr == null)
        {
            return false;
        }

        //matcher method attempts to find match between given time and regex
        Matcher m = p.matcher(timeStr);
        //if given time and Regular expression matches,return true.
        return m.matches();

    }

    public static void main(String[] args) {

        Scanner myScanner = new Scanner(System.in);
        System.out.println("Enter time in 24 hr format (HH:mm): ");

        String timeIn = myScanner.nextLine(); // read user input
        while(!(validateTime(timeIn)))
        {
            System.out.println("Please enter valid time: ");
            timeIn = myScanner.nextLine();
        }

        System.out.println("Current Time is: "   timeIn);
        //String[] arrOfStr = timeIn.split("\\:");

        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HH:mm");
        LocalDateTime datetime = LocalDateTime.parse(timeIn,formatter);
        String updatedTime = datetime.minusMinutes(45);
        System.out.println("New time to wake up: "   updatedTime);

CodePudding user response：

You need to add a toString() to stringify the time object. Also, as you're only reading a time, use LocalTime instead of LocalDateTime Your last few lines would then look like:

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HH:mm");
    LocalTime datetime = LocalTime.parse(timeIn, formatter);
    String updatedTime = datetime.minusMinutes(45).toString();
    System.out.println("New time to wake up: "   updatedTime);